School Science Lessons
UNPhysics1, conduction, convection, current electricity, density, heat and temperature, heat radiation, static electricity
Please send comments to: J.Elfick@uq.edu.au
2012-01-28 SP
Table of contents
4.16.0 Conduction of heat
4.24.0 Convection
4.51.0 Current electricity
4.12.0 Density
4.5.0 Heat and temperature
4.35.0 Heat radiation
4.39.0 Static electricity
4.16.0 Conduction of heat
4.21 Conduction of heat by a coin on paper
4.17 Conduction of heat by metals, Davy lamp
4.22 Conduction in a metal bar
4.20 Copper coil candle snuffer
4.16 Reduce heat loss with insulation
4.24.0 Convection
4.27 Convection box, convection currents in air
4.30 Convection currents and ventilation
4.25 Convection currents in a container
4.24 Convection currents in a test-tube
4.26 Convection currents from an ink bottle
4.29 Convection disc, heat snake, convection wheel
4.31 Temperature of water at maximum density, 4ºC
4.28 Trace convection currents
4.51.0 Current electricity
4.61 Cells in parallel
4.60 Cells in series
4.59 Circuit board
4.58 Conductors and non-conductors of electricity
4.53 Dry cell, electric torch (flashlight) battery, Leclanche cell
4.54 Dry cells in an electric circuit
4.66 Electric current detector
4.65 Electric light bulb, incandescent filament lamp, light globe
4.62 Electric light bulbs (lamps) in series and parallel, resistors in series and parallel
4.57 Electric torch (flashlight)
4.52 Electricity from a lemon, lemon cell
4.51 Electricity from two coins
4.63 Fuse, Make a fuse
4.64 Fuse, Use a fuse
4.55 Simple switch
4.56 Switches in a circuit
4.12.0 Density
4.12 Density of a solid
4.13 Density of a liquid, relative density
4.5.0 Heat and temperature
4.3 Plug and ring experiment
4.5 Bimetallic strip, compound bar
4.9 Burn candle over water
4.6 Expansion and contraction of liquids
4.4 Expansion of a solid when heated
4.8 Expansion of air
4.1 Temperature rise and quantity of heat intake
4.2 Transfer kinetic energy to heat energy
4.11 Heat energy to change liquid to vapour, boiling point, latent heat of vaporization
4.10 Heat energy to change solid to liquid, melting point, latent heat of fusion
4.37 Heat and temperature
4.14 Test a liquid in glass thermometer
4.35.0 Heat radiation
4.35 Feel heat radiation
4.33 Focus radiant heat waves
23.8.5 Reflection of radiant heat waves
4.15 Thermoscope to compare absorption of radiation
4.32 Transfer heat by radiation
4.39.0 Static electricity
4.138 Attract water to a comb
4.139 Balloon stays in place
4.141.1 Coin stays on the cupboard door
4.144.0 Electroscope, metal foil ball electroscope, metal foil ball electroscope
4.144.1 Gold leaf electroscope
4.50 Many charges from one source, electrophorus
4.141 Newspaper stays on the wall
4.147 Pith ball indicator
4.140 Repulsing balloons
4.142 Static electricity detector
4.137 Static electricity from rubbing
4.146 Two kinds of static charge
4.40 Van de Graaff generator
4.1 Temperature rise and quantity of heat intake
See diagram 23.103: Temperature rise and quantity of heat intake
1. Put a large iron bolt and a nut for the bolt in a container of boiling water to bring them to the same temperature. Put equal volumes of water in two containers with each volume enough to immerse the bolt. Put the hot bolt in one container and the hot nut in the other container. Record the temperature of the water in each container after the same period. The difference in temperature change of the water in the two containers is because of the different amounts of heat stored in the iron bolt and the iron nut.
2. Check if your temperature sense is reliable. Use containers of hot water, warm water and cold water. Put both hands in the warm water. The hands feel the same temperature. Put one hand in the hot water and the other hand in the cold water. Quickly dry your hands and put them both into the warm water again. The two hands do not feel the same temperature. Is your temperature sense reliable? This may be a silly experiment but it shows that your temperature sense is not always reliable.
4.2 Transfer kinetic energy to heat energy
See diagram 23.104: Transfer kinetic energy to heat energy
Use a small piece of lead sheet wrapped around one end of a piece of thin iron wire. Hold the other end of the wire. Hit the lead several times with a hammer. Feel the temperature rise as heat moves along the wire towards your hand.
4.3 Plug and ring
See diagram 23.105: Ball and ring
1. Use a large metal screw and a screw eye through which the head of the screw just passes. Alternatively use a metal ball which just passes through a metal ring, or a bar that will just pass through a gauge. Attach the screw and screw eye into the ends of a stick. Hold the stick to heat the head of the screw in a burner flame. Try to pass the screw through the screw eye. The screw cannot pass because of expansion due to heating. Keep the screw hot and heat the screw eye in the flame simultaneously. Now the screw head can pass through the screw eye. Keep the screw head in the flame and cool the screw eye in cold water. The screw head cannot pass through the screw eye. If you cannot open a jar with a metal screw top, hold the jar upside down so that the metal screw top is touching hot water. The metal screw top expands and you can open the jar.
2. Use an iron ring with a set of two balls one over size and one under size. Heat the ring and slip over both metal balls. A ball passes through a ring only when the ring is heated.
3. Leave the over size ball in liquid nitrogen for ten minutes then try to pass the ring around it.
4.4 Expansion of a solid when heated
See diagram 4.4: Expansion of a solid when heated
Use a 2 m piece of stout copper tubing. Put it on a table and fix one end with a clamp. Underneath the other end put a bicycle spoke to act as a roller. A drinking straw fixed to the roller by wax will show any movement of the rod resting on it. Blow steadily down the tube between the fixed end and the middle. This arrangement detects the expansion of the tube caused by the hot breath. Pass steam through the tube and note the motion of the pointer. Repeat the experiment with different types of tubing.
4.5 Bimetallic strip, compound bar
See diagram 23.107: Bimetallic strip
Coefficient of liner expansion of brass = 19 X 10-6 K-1 at 0oC.
Coefficient of liner expansion of invar steel = 1.2 X 10-6 K-1 at 20oC.
Invar" is trade name for alloy, composed of iron 63.8%, nickel 36%, carbon 0.2%. Invar is abbreviation of "invariable". It is used in surveyors' measuring tapes, pendulums, and tuning forks. Bimetallic strips are used to switch thermostats and fire alarms on or off.
1. Strips of dissimilar metals bonded together bend when heated. Heat a bimetallic strip of brass and steel in a Bunsen burner flame. A pair of iron and brass strips riveted together bends when heated because of the difference of expansion of the two metals. The strip curves towards the steel side because the brass expands more.
2. Mount a pointer on the end of a bimetallic strip. Use two 25 cm strips of brass and invar steel welded together as a bimetallic strip.
3. Make holes in the metal strips with a nail and fix small tacks as rivets.
4.6 Expansion and contraction of liquids
See diagram 23.108: Expansion and contraction of liquids 1| See diagram 23.109: Expansion and contraction of liquids 2
1. Fit a flask with a one-hole stopper and a 30 cm length of glass tubing that extends into the flask. Add coloured water to the flask so that it extends 5 cm up the glass tubing. Slowly heat the flask while carefully watching the level of coloured water in the glass tubing. When you heat the flask, the water level initially falls as the glass in the flask expands then rises as the water expands. Cool the flask under the tap. The level of coloured water in the glass tubing first rises as the glass in the flask contracts then drops as the coloured water cools and contracts. So the expansion of liquid you see in a thermometer is really the expansion of liquid less the expansion of the glass tube.
2. Use two identical small bottles fitted with one-hole stoppers and glass tubing passing though into the bottles. Fill the bottles with different liquids. Put the bottles in a container of hot water. The different rise of liquids inside the glass tubing shows the difference in expansion of the different liquids.
3. Place some coloured water in a flask. Insert a one-hole stopper and glass tube so that it extends downward into the fluid and upward. Pour warm water over the flask and the coloured water rises in the tube. Pour cold water and the coloured water drops inside the tube.
4.8 Expansion of air
See diagram 23.110: Expansion of air
1. Use a flask fitted with a one-hole stopper and glass tube that extends into the flask. Put a small amount of oil in the glass tube to trap air in the flask. Hold the flask in your hands. The oil moves up the tube because the heat from your hands causes the trapped air to expand. If you look carefully note that the oil first moves down because the heat from your hands first causes the glass of the flask to expand. When you cool the flask under the tap, the oil moves down.
2. Fit a hard glass test-tube with a one-hole stopper that has a length of glass tubing through it. Invert the test-tube so that the end of the tubing is in a container of water. Clamp the test-tube in an inverted position so that you can heat it with a burner. Heat the test-tube and note the bubbles from the end of the tube in the container of water. Heat has caused the air to expand. Cool the test-tube by pouring cold water over it. Water moves up the glass tubing as the cooling air contracts.
3. Fit a toy balloon over the neck of a small flask. Put the flask in a container of water. Heat the water. The balloon expands as the heated air in the flask expands. Partially inflate a balloon and tie the neck tightly. Leave it in a warm place or in the sunlight. The balloon becomes fully inflated as the air inside expands when heated.
4.9 Burn candle over water
See diagram 4.9: Burning candle over water
Attach a tall candle and a short candle to the bottom of a trough. Add water to the trough and note the water level. Light both candles. Put a large jar upside down over the candles. The tall candle extinguishes first then the short candle. Hot gas products of combustion, including carbon dioxide gas, have filled the jar from the top down to extinguish the candle flames. Some hot gases push out under the rim of the jar to form bubbles around the jar in the trough. When the candles are extinguished, the hot gases cool and contract to form a partial vacuum, and the water level rises inside the jar
4.10 Heat energy to change solid to liquid, melting point, latent heat of fusion
See diagram 24.10.0: Liquid naphthalene solidifies | See diagram 24.2.3: Temperature, energy (time) heating curve for water
Put crushed naphthalene or ethanamide (acetamide) in a test-tube in a container of water. Heat gently until all the substance has melted. Remove the test-tube from the container and fix a thermometer with its bulb in the melted substance. Stir the substance with a thermometer while the substance cools and record the temperature every 30 seconds for 6 minutes. Plot a graph of temperature against time. At first the temperature drops while the substance remains liquid. Then the temperature remains the same while the substance changes from liquid to solid. When all the substance is solid, the temperature starts to drop again. The melting point, m.p., is the temperature when a solid changes to a liquid. The specific latent heat of fusion of a substance, L, is the quantity of heat required to change one kilogram of the substance from solid to liquid without change in temperature. The unit is joule / kg, J kg-1. The specific latent heat of fusion of ice = 3.34 X 105 joule / kg, 334 kJ kg-1.
4.11 Heat energy to change liquid to vapour, boiling point, latent heat of vaporization
See diagram 23.11.0: Heat required to vaporize a liquid | See diagram 24.2.3: Temperature, energy (time) heating curve for water
1. Weigh a container, add 50 mL water and weigh again. Heat the container and water. Put a thermometer in the water and record the rise in temperature every 30 seconds. Plot a temperature against time graph. Draw the line of best fit and calculate the average temperature increase per minute. Assume that all the heat goes into the liquid and the heat absorbed by the flask is small. Calculate the heat absorbed by the liquid per minute by multiplying the mass of the liquid by its specific heat and by the temperature increase per minute.
2. Weigh a container, add 50 mL water and weigh again. Heat the container and water and leave to boil for 10 minutes. Leave to cool then weigh the container and water. Calculate the mass of water lost by evaporation. This will be the heat of vaporization of the liquid.
3. Put a known mass of water in a boiling flask and a known mass of water in a container. Record the temperature of the water. Heat the boiling flask and pass all the steam into the water in the container so that all the steam condenses to water. When most of the water in the flask has evaporated, stop heating and record the temperature of the water in the container. Leave the apparatus to cool to room temperature, weigh the water remaining in the flask and the water in the container. The condensing steam loses latent heat of fusion when it condenses and loses heat when its temperature (100oC) falls to the temperature of the water in the container. The specific latent heat of vaporization of water is 4.26 MJ kg-1.
4.12 Density of a solid
The density of a solid is the ratio of mass to volume (mass per unit volume). Use a balance to measure the mass. If the solid is insoluble in water, measure the volume by displacement of water. Half fill a graduated cylinder with water. Note the reading. Immerse the solid in the water and note the reading again. The volume of the solid is the difference in the two readings.
Examples of the densities of elements, in g cm-3, are as follows: aluminium: 4.70, carbon (graphite): 4.25, carbon (diamond): 3.51, copper: 8.92, gold: 19.30, helium: 0.147, hydrogen gas: 0.070, iron: 7.86. lead: 11.30, magnesium: 1.74, mercury: 13.60, nickel: 8.90, platinum: 21.40, silver: 10.50, uranium: 19.10, zinc 7.14. Measure the density of examples of different metals then decide whether they are pure substances.
In SI units, measure density in kg m-3, e.g. density of dry air at sea level = 1.29 kg / m3.
4.13 Density of a liquid, relative density
1. Weigh a small container with the liquid inside. Pour the liquid into a graduated cylinder to find the volume of the liquid. Use a balance to find the mass of the container and the mass of liquid transferred to the measuring cylinder. Obtain the density by dividing the mass of the liquid by the volume.
2. The density of water is close to 1 g per cc, (1g cm-3), so you can compare the density of substance with the density of water as relative density, RD. Relative density (formerly specific gravity, G), is the ratio of mass of a volume of a substance to the mass of an equal volume of water, at 4oC.
Relative density has no units because it is a ratio. Examples of relative density include the following: e.g. petrol (r.d. 0.70), ethanol (r.d. 0.79), ice (r.d. 0.90), olive oil (r.d. 0.92), water (r.d. 1.00), sea water (r.d. 1.03), glass (r.d. 4.50), mercury (r.d. 13.60), gold (r.d. 19.30).
A special bottle, a density bottle, gives an accurate measure of relative density.
Mass of empty density bottle = A
Mass of bottle + liquid = B
Mass of liquid = B – A
Mass of bottle + water = C
Mass of water = C – A
RD = B – A / C – A
However a more convenient way to measure the density of a liquid is to use a hydrometer.
3. Find the density of a cola drink in an aluminium drink-can. Weigh the full aluminium can. Open the aluminium can and drink the cola. The weight of the aluminium can is approximately 13 g. The volume of the cola is written on the side of the aluminium can, e.g. 375 mL or 355 mL (12 oz). Calculate the density of the cola. Density  = weight of unopened can of cola - 13 g / volume of cola mL. Repeat the experiment with "diet" cola where sugar is substituted by a chemical sweetener, e.g. phenylalanine, aspartame.
4.14 Test a liquid in glass thermometer
Use a thermometer with a scale, e.g. a mercury or alcohol thermometer, -10oC to 110oC. Also, use a tall flask containing coloured water fitted with a one-hole stopper and glass tube extending into the bottle. Attach a blank scale to the glass tube. A thermometer scale has two fixed points, the lower fixed point and the upper fixed point.
Put the bulb of a thermometer in crushed ice that is melting. Check that the temperature is 0oC on the calibrated thermometer. Mark the lower fixed point on the blank scale.
Put a thermometer in steam immediately above the surface of boiling water. Check that the temperature is 100oC on the calibrated thermometer. Mark the lower fixed point on the blank scale. Divide the distance between the upper and lower fixed point to obtain 100 marks representing a temperature difference of 1oC. If you do the experiment on a mountain at a high altitude, the temperature of boiling water will be below 100oC because of the reduced atmospheric pressure. If you do the experiment in a submerged submarine, the temperature of boiling water may be above 100oC because of the increased pressure with depth. The thermometer in the boiling water reads exactly 100oC only at sea level or where the barometer reading is 760 mm of mercury.
4.15 Thermoscope to compare absorption of radiation
See diagram 23.116: A simple thermoscope
Experiment with different materials before doing this experiment because for most cloths the absorption of infrared is almost independent of colour. The amount of surface area pointing towards the source is also a variable. Use two identical clear plastic bottles. Put a dark coloured piece of cloth or plastic in one bottle. Put an identical amount of white cloth or shiny metal foil in the other bottle. Fit the bottles with one-hole stoppers with 20 cm of glass tubing. Into each glass tube introduce a bead of water or oil. Place each bottle in the sun, or about 50 cm from a bright light bulb or 1 metre from a fire or 20 cm from a burning lamp or candle. Note the rate at which the beads of water or oil rise in the tubes.
4.16 Reduce heat loss with insulation
Use four large tin cans of equal size and four smaller tin cans of equal size. Inside the first large can put a small can on two corks in a large can. This is the control. Select types of insulating material, e.g. sawdust, cork pieces, newspaper, plastic. Put a small can inside each large can. Pack one type of insulating material under and around each of the smaller cans. Put a cardboard cover on each large can. Make a hole in each cover for a thermometer. Fill each small can to the same depth with water that is nearly boiling. Record the initial temperature of the water in each can. Record the temperature of the water in each can at five minute intervals. Draw cooling curve graphs by plotting temperature against time for each can. Note which material is the best insulator.
4.17 Conduction of heat by metals
See diagram 23.119: Davy lamp
1. With your fingers hold a wire coat hanger horizontally over a flame a small distance from directly above the flame. Soon the wire becomes too hot to hold. Move your fingers back but keep the coat hanger in the same position. Feel heat moving along the wire.
2. Use identical lengths of different metal bars or rods with the same diameter, e.g. copper, brass, aluminium, iron. Put blobs of melted candle wax at the same intervals along the bars. Push small nails or metal pieces into the wax while the wax blobs are still soft. Heat one end of each metal bar. The blobs of wax melt and the nails fall down as heat moves along the bar. The metals do not conduct heat equally.
3. Hold a sieve or a piece of metal gauze, e.g. 1 mm iron gauze or metal fly-wire screen, over the flame of a small candle. (Some fly-wire screens consist of fibreglass or plastic, so do not use this type of screen.) As you lower the wire gauze, the flame gets smaller. The flame does not go through the wire netting. The flame becomes smaller because the wire conducts the heat away from the flame so the temperature is lowered. Sir Humphry Davy used this observation to invent the . Metal gauze around the flame in the lamp conducts away the heat so that the flame cannot ignite explosive gas in the coal mine.
4. Put an unlit burner under a tripod stand and cover it with 1 mm iron gauze. Turn on the gas and ignite it above the metal gauze. The gas burns only above the wire gauze screen because it conducts away the heat and prevents the gas below it from reaching ignition temperature.
5. Hold a piece of paper above a candle flame. The paper chars. Put a metal coin or a key on the paper and hold it over the candle flame. The metal conducts the heat away from the paper and leaves a pattern where the metal touches the paper.
4.20 Copper coil snuffer
See diagram 4.20: Copper coil snuffer
Place a coil of heavy copper or aluminium wire over the flame of a candle. The flame goes out. You can snuff out a candle flame by depriving it of oxygen but here the oxygen can easily get to the flame. The fire goes out because the coil of heavy wire conducts the heat away from the flame so fast that the temperature is lowered below the ignition temperature. This shows that copper and aluminium are good conductors of heat. If the flame is too large, it will produce heat energy too rapidly to be carried away by the coil. If the coil is already hot before the experiment, the temperature of the flame may not be lowered enough to extinguish the flame.
4.21 Conduction of heat by a coin on paper
Hold a piece of paper above a candle flame: it will char if brought near. Place a metal coin on the paper and repeat the experiment: the metal will conduct the heat away and leave a pattern on the paper.
4.22 Conduction in a metal bar
See diagram 23.1.2: Heat conduction of different metals
Use a bar of copper, brass or aluminium at least 30 cm long. Place blobs of melted paraffin wax at 3 cm intervals. While the paraffin blobs are still soft, push the pointed ends of nails or tacks into them. Heat one end of the box with a flame. Note the evidence that heat moves along the bar by conduction.
4.24 Convection currents in a test-tube
See diagram 23.1.8
Fill a test-tube with cold water. When the water is still, add a very small crystal of potassium manganate (VII) and let it fall to the bottom leaving little colour trace. Hold the test-tube in the bare fingers near the top but not above water level. Heat with a very small burner or candle flame at the bottom of the tube. You can hold the warm test-tube with bare fingers. Note the movement of the coloured dye from the crystal in the convection current. Repeat but heat very gently near the top of the water surface, while holding the test-tube near the bottom.
4.25 Convection currents in a container
1. Weigh an empty container. Fill a container exactly with cold water and weigh it again. Empty the container and fill it exactly again with the same volume of hot water and weigh it again. The same volume of hot water weighs less than cold water. When you heat water the lighter warm water nearer the source of heat displaces the heavier cold water and convection currents occur. Hot water is less dense than cold water.
2. Fill two identical containers with water near 100oC and near 0oC.  Drop 5 drops of food colouring  into the water in different places in the containers containers. Observe the spread of the food colouring. The food colouring mixes more quickly with the hot water because its molecules are moving faster around each other. In the cold water, the food colouring may just sink to the bottom to displace water by its own weight.
4.26 Convection currents from an ink bottle
See diagram 23.126: Convection currents from an ink bottle
Use a small ink bottle, fitted with a two-holes stopper. Cut two pieces of glass tubing. One piece should extend from the stopper almost to the bottom of the bottle. The other piece should extend 5 cm up from the stopper. Fill a large container with cold water. Fill the small bottle with hot coloured water. Put the small bottle in the bottom of the large container while holding the fingers over the ends of the tubing. The hot coloured water rises in the large container as the cold water enters the bottle.
4.27 Convection box, convection currents in air
To make a convection box, cut away one side of a box and replace it with glass. Cut two holes 2 cm diameter and 10 cm apart in the top of the box. Attach two tubes above the holes to be chimneys. Put a candle in the box under one chimney. Light the candle. Hold the smoking paper above each chimney. See the convection currents through the glass side of the box.
Another way of showing air current is by making use of the difference in refractive indexes of warm and cold air. A car headlight bulb without a reflector will cast “shadows” of convection current from an electric heater.   Look at an object on the other side of a hot engine or a hot road. The object will appear distorted because the refractive indexes of warm and cold air are different. This is one cause of mirages in the desert.
4.28 Trace convection currents
See diagram 4.28: Trace convection currents
Hang a T-shape piece of cardboard from the rim of a large container. The stem of the T-shape should reach half way down the container. Use a wire loop to lower a lighted candle into one side of the container. Use smoking paper to find the convection currents in the container. Use smoking paper to trace the air currents around a candle, in a room heated with a stove, at different levels above the floor, with windows open at the top and bottom, in a doorway between a warm and cold room.
4.29 Convection disc, heat snake, convection wheel, hot hand
See diagram 23.127: Convection disc, heat snake
1.1 Convection disc. Use a disc of thin tin from the end of a cylindrical metal can. Cut four blades all round the disc and pivot it on a bent knitting needle. Hold the disc above a candle flame, and it will revolve rapidly. A paper spiral supported on a knitting needle will revolve in a similar way.
1.2 Use a disc of tin cut from the top of a metal can. Make four radial cuts and bend the tin to form four propeller blades. Balance the disc on the end of a bent wire. Hold the disc above a candle flame. The disc revolves as rising air hits the blades.
1.3. Make a more sensitive convection wheel from the metal foil top of a milk bottle.
2. Heat snake. Cut paper into a spiral. The centre of the spiral is like the head of a snake. Support the head of the snake on a wire over a candle. The heat snake turns around the candle.
3. Hot hand. Fold a rectangular piece of paper along the middle and across a diagonal. Balance the folded paper over the end of a sharp pencil where the two folds cross. Keep still while holding the pencil tightly in your fist. The folded paper will start to revolves as heat rises from your hot hand.
4. Look at an object on the other side of a hot engine or a hot road. The object will appear distorted because the refractive indexes of warm and cold air are different. This is one cause of mirages in the desert.
4.30 Convection currents and ventilation
See diagram 23.128: Convection current ventilation
Use a box with grooves for a lid and cut a glass window that slides in the grooves to make an airtight fit. Bore four holes in each end. Each end represents a window. The top holes of each side are the top halves of each window. Put four candles in the box, light them and close the sliding glass. To study the best conditions for ventilation, put solid corks in the openings, close completely both windows, and note the candles.
Try the following different combinations of opening:
1. one window open at the top and bottom, i.e. all four holes in one side open,
2. one window open at the top and the other at the bottom,
3. both windows open at the top, one window open at the bottom,
4. both windows open at the bottom, one window open at the top. Find which window openings provide the best ventilation.
4.31 Temperature of water at maximum density, 4oC
1. Fill a bottle with water and put the top on securely. Wrap the bottle in a cloth, to prevent the shattered glass from falling. Put the bottle into the freezing compartment of a refrigerator. After 24 hours, remove the bottle and examine it. The bottle may be cracked because of pressure from the expanding ice.
2. Put a large piece of ice into a glass of water. Arrange two thermometers so that they measure the temperatures near the top and the bottom of the water. The water cooled by the ice falls to the bottom. This fall continues until the water at the bottom of the glass reaches a temperature of 4oC. The water stays at this temperature for a long time, the colder water remaining higher up near the ice. So water at 4oC is denser than the water at 0oC, so a pond freezes from the surface downwards while the bottom seldom falls below 4oC.
3. To study the expansion of freezing water, use two identical drinking cups. Fill the first cup with tap water at room temperature so that the water heaps up to form a meniscus. Put the second cup in the freezing compartment of the refrigerator then add extra water to the cup to get the highest possible meniscus. When the water in the cup is frozen, compare the meniscus of the frozen water with the meniscus at room temperature. The frozen water heaped up because it had expanded. Water has a maximum density at 4oC. When water cools from room temperature to 4oC, it contracts in volume. When water cools from 4oC to 0oC, it expands in volume. At 4oC the density of water is 1000 kg m-3 (1 g per cc). At 0oC the density of water is 999.87 kg m-3 and the density of ice is 918 kg m-3, so ice floats on water.
4.32 Transfer heat by radiation
Hold the palm of your hand very close to, but not touching, your cheek. Feel the radiation from your hand. Heat travels by radiation almost instantaneously. Hold your hand under an unlighted electric light bulb, the palm upward. Turn on the electricity and feel the heat from the light bulb. The heat could not reach your hand so quickly: a) by conduction because air is a very poor conductor of heat or b) by convection because convection carries the heat upward and away from your hand. The heat came to your hand carried by short electromagnetic waves of wavelengths longer than light. Radiation carries heat in every direction from the source. Put a piece of glass between a light bulb and your hand to block any movement of air. Feel the radiated heat.
4.33 Focus radiant heat waves
See diagram 23.3.7
Use a magnifying glass to focus the rays of the sun on a piece of paper tissue. The paper chars and catches fire. Repeat the experiment with paper tissue soaked in black ink. The black paper catches fire sooner than the white paper. Repeat by focussing the sun's rays on your arm. A bright spot forms and you can feel the hot spot. Note the distance of the lens from your arm when the spot is smallest and brightest. This distance is the focal length of the lens. Notice the distance when the spot feels hottest. The two distances are different.
4.34 Reflection of radiant heat waves
See diagram 23.3.7
Heat tissue paper with a magnifying glass. Note the distance from the reading glass to the tissue paper. Put a tilted mirror half way between the lens and the paper. Feel with your hand above the mirror until you find the point where the heat waves are focussed. Hold a piece of paper tissue at this point. The paper ignites.
4.35 Feel heat radiation
1. Stand near an open window to feel the radiation from the sun on your cheek. Close the window. You can still feel the radiation from the sun on your cheek.
2. Hold your cheek 25 cm from a hole in a wooden sheet placed in front of a heating element. Feel the radiation on your cheek. Put a piece of glass between your cheek and the hole. Feel the radiation on your cheek. Repeat the experiment using more sheets of glass.
4.37 Heat and temperature
See 22.2.0 Heat and temperature, joule, calorie
4.40 van de Graaff generator
Order online: Fun Fly Stick, portable van de Graaff generator
Van de Graaff generator, distribution of charge on a conductor, proof plane, action of points, lightning conductor
This electrically driven generator with a 200 mm conducting sphere, capacity 15 pF, can be use to generate high direct voltages of 15 to 200 KV using a high speed fabric belt to accumulate charge in a large Faraday cage, i.e. the conducting sphere. A charge is applied to the belt from a point below, then carried up into the hollow sphere where a collector removes the charge from the belt and stores it on the sphere. Examine sparks from a Van der Graaff generator to a nearby grounded ball.
A van de Graaff generator has an endless belt made of insulating material, e.g. rubber or plastic, that is pulled over a Perspex roller by an electric motor. The upper end of the endless belt is inside a large metal dome. The moving belt forced charges onto the dome so that it gets to a very high voltage.
1. Attach a wire to a needle. Touch the other end of the wire to the metal dome and point the needle at a candle flame. The flame appears to be blown away by a wind.
2. Bring a small metal sphere near the metal dome and note the "lightning" spark.
3. Touch the metal dome and note your hair standing on end.
Commercial
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4.50 Many charges from one source, electrophorus
See diagram 31.1.8.1: Many charges from one source, electrophorus
Use a piece of aluminium or a cake tin. Heat the metal evenly over a flame. Touch a wax candle to the centre of the aluminium until it melts and sticks solidly to it as a handle. Use a plastic dish pan or bowl larger than the cake tin. Put the bowl or pan on a table and stroke the inside bottom of the pan briskly with a piece of fur or flannel for half a minute. Put the aluminium on the plastic and press it down hard with your fingers. Remove the aluminium pan, put your finger near the metal and you should get a spark. You can take many charges from the plastic without more rubbing. Press the metal against the plastic, press with your fingers and lift by the handle.
4.51 Electricity from two coins
Take two coins made of different metals. Clean them well with steel wool or fine sand paper. Fold some paper into a pad so that it is larger than the coins. Soak the paper in saltwater. Place one coin on top of the pad and the other underneath. Hold them between your thumb and finger. Connect both leads of a sensitive galvanometer or multimeter to the coins and note the deflection.
4.52 Electricity from a lemon, lemon cell
See diagram 32.149: Lemon cell
Connect a wire to a piece of zinc. Use zinc cut from the can of a used dry cell, torch battery. Connect another wire to a piece of copper. Roll a lemon on the table with your hand to break up some tissue inside. Push the zinc and copper strips through the skin of the lemon so that they do not touch. Connect both leads of a sensitive galvanometer or multimeter to wires and note the deflection. Repeat the experiment using a potato. Note whether the distance between the metal strips affects the galvanometer reading.
4.53 Dry cell, electric torch (flashlight) battery, Leclanche cell
See diagram 32.150: Battery cut vertically
The term "battery" refers to several joined electrical cells, but one dry cell is commonly called a "battery", e.g. a torch battery, flashlight battery
A Leclanche cell (Georges Leclanche 1839-1882) is a primary voltaic cell with a carbon rod anode, zinc cathode, dilute ammonium chloride solution electrolyte and e.m.f. approximately 1.5 volts.
Zn + H2SO4 --> (discharge) ZnSO4 + H2O + H2 (g)
A torch "battery" is the dry cell version of the Leclanche cell. It has manganese dioxide [manganese (IV) oxide] around the carbon rod to oxidize hydrogen gas and so depolarize the anode.
2MnO2 + H2 --> Mn2O3 + H2O
The electrolyte is in the form of a water paste so the dry cell is not really "dry".
Remove the outer covering from an old dry cell. Use a saw to cut the cell in half and note its structure. Note the carbon (+ve) pole in the centre. The zinc container is the negative (-ve pole). The material between the two poles is the electrolyte. Note how the zinc has been eaten away by the chemical
4.54 Dry cells in an electric circuit
See diagram 32.3.9.1d: Cells in a circuit | See diagram 32.151.2: Torch battery electrical experiments
Connect an electric light bulb, e.g. 4.4 volts, V, 0.5 amps, A, and a lampholder, to the +ve and -ve terminals of a dry cell or a lead cell accumulator or a low voltage power supply. Notice the filament made of tungsten carbide. Passage of the electric current through the tungsten carbide wire causes it to become very hot and give off light. Reverse the connections to the source of electricity and the lamp still operates although the electricity is flowing in the opposite direction. Draw a diagram to show the path of the current through the light bulb and around to the other end of the cell. This is a simple electric circuit. Use circuit diagrams to represent the electrical components in a circuit.
4.55 Simple switch
See diagram 32.152: Simple switch
1. Fasten the end of a piece of wire to a pencil with two rubber bands. A second wire makes a connection.
2. Put a knife switch in a circuit with a dry cell and a light bulb. Turn the light on and off by operating the switch. Replace the light bulb with a bell or buzzer and operate the switch. Replace the knife switch with a push button switch. Examine the construction of different switches, e.g. household tumbler switch, rocker switch. Use them in a circuit.
4.56 Switches in a circuit
Put a knife switch in a circuit with a dry cell and a light bulb. Turn the light on and off by operating the switch. Replace the light bulb with a bell or buzzer and operate the switch. Replace the knife switch with a push button switch. Examine the construction of different switches, e.g. household tumbler switch, rocker switch. Use them in a circuit.
 4.57 Electric torch (flashlight)
See diagram 4.57: Electric torch (flashlight) | See diagram 32.154.1: Electric torch
Take apart an electric torch (e.g. one with a current of 0.5A at 2.4V) to see the different parts. Draw a circuit diagram. Note the directions of insertion of batteries.
4.58 Conductors and non-conductors of electricity
See diagram 32.155: Test conductivity
Use a simple electric circuit to test whether different substances conduct electricity, e.g. paper, rubber eraser, plastic, key, coin, cloth, string, chalk, glass, pin, nail file, insulated wire, bare wire, a finger and water. Test these in a circuit across an open knife switch. Materials that carry electricity are electrical conductors, or simply conductors. Materials that do not carry electricity are non-conductors, or insulators. The copper core of bell wire is a conductor. Its covering is an insulator.
4.59 Circuit board
Use a piece of heavy cardboard measuring 30 x 30 cm as a base. Fix clips on it to hold the cells, and sprung metal strips to provide connections between cells. Screw brass curtain rod holders into the base. Make spring connectors of varying lengths from curtain wire with hooks at each end. Put light bulb holders into circuits with curtain wire connectors or heavy uninsulated copper wire. Make other connections with lengths of uninsulated copper wire attached to crocodile clips.
4.60 Cells in series
See diagram 4.60: Cells in series | See diagram 32.2.1.1: Cells in series and parallel | See 32.5.1.1: Series circuits (Motor vehicles)
Connect two dry cells or lead cell accumulators so that the negative terminal of one is in contact with the positive terminal of the other. Connect them in series. Put a light bulb in the circuit. Close the circuit with one cell, two cells, three cells in series. Record the changes in the brightness of the light bulb. The brightness of the light depends on the number of cells connected in series. When you connect cells in series, the total voltage is the sum of the individual voltages of the cells. If you use 1.5V cells, then two cells give 3V, and three cells give 4.5V, four cells give 6V. The current will change.
4.61 Cells in parallel
See diagram 4.61: Cells in parallel | See diagram 32.4.6.1: Cells in parallel | See 32.5.1.2: Parallel circuits (Motor vehicles)
Connect two or three fresh dry cells or lead cell accumulators so that their positive terminals are joined and their negative terminals are joined. They are connected in parallel. Set up a circuit on a circuit cardboard with three cells in parallel. Disconnect one or two of the cells. The circuit is not broken and the brightness of the light does not change. The voltage drop in the circuit is the same if one, two or three cells are used. The total current is unchanged. If four cells in the circuit, the total current is 0.125 x 4 = 0.5 amps.
4.62 Electric light bulbs (lamps) in series and parallel, resistors in series and parallel
Electric light bulbs in series and parallel
See diagram 32.157: Resistors in series | See diagram 32.158: Resistors in parallel
If resistors with resistance R1, R2 and R3 are connected in series, they have the same current, I, passing through them. and total resistance of the circuit = R1 +R2 + R3 ohms.
If resistors with resistance R1, R2 and R3 are connected in parallel, they have a common potential difference across them, V, and the total current through them is the sum of the separate currents I1 + I2 + I3. If total resistance is RT, then 1/RT = I/R1 + I/R2 + I/R3. So the total resistance will be less than the smallest resistance in parallel.
1. Connect one, two and three identical light bulbs in series. Record the brightness of the light bulbs.
2. Connect one, two and three light bulbs in parallel. Record the brightness of the light bulbs.
If you connect six light bulbs in series in a circuit containing a 6 V battery, each light bulb receives 1 V. If you connect six light bulbs in parallel in a circuit containing a 6 V battery, each light bulb receives 6 V.
When bulbs are connected in series, the total voltage is divided between them, e.g. if three bulbs are connected in series to a 3 volt battery, each bulb receives 1 volt.
When lamps are connected in parallel, each bulb receives the full voltage of the supply.
4.63 Make a fuse
See diagram 32.160: How a fuse works
Examine normal and burnt out fuses. You use fuses to protect electric circuits against overloading. The fuse wire melts and breaks the circuit when an unsafe amount of current is flowing. Use a thin strip, no more than 0.5 mm wide, of metal foil cut from a chocolate wrapper or a thread of steel wool. Fasten it between the ends of two wires projecting through a cork. Pass electric current through the fuse until the fuse wire melts and breaks.
A short circuit is the deviation of a current from the planned path along a path of less resistance. However this excess current can be stopped if a suitable fuse exists in the circuit.
4.64 Use a fuse
See diagram 32.160: Use a fuse
1. Place the model fuse from experiment 4.63 in a circuit in series with three cells and a light bulb. Use a crocodile clip to short circuit the light bulb. If the fuse does not melt, cut a thinner strip of foil. Try different kinds and widths of foil until the foil carries the current when connected properly but melts when a “short” occurs in the circuit. Then replace the fuse and add more light bulbs in parallel until the fuse burns out.
2. Open the fuse box at your school or home. Note the different kinds of fuses, how to “trip” a fuse and how to replace the fuse wire. A fuse box should contain spare fuse wire. When you use several appliances simultaneously, the wires carrying the current may become overheated and cause a fire. Be careful! Putting a coin behind a fuse to allow more current to flow is a very dangerous practice. Use the correct fuse wire. A 30A fuse in a circuit designed for a 15A fuse is unsafe.
4.65 Electric light bulb, incandescent filament lamp, light globe
See diagram 32.162: Heat and light from electricity  | See 4.116: Incandescent lamp
A substance is incandescent if it emits light as a result of its temperature being raised.
1. Heat source.
1.1 Remove the shade from a bed lamp containing a 100 W incandescent electric light bulb. Cover the bulb with very thin aluminium sheet, e.g. aluminium cooking paper.
1.2 Insert a 100 watt pearl electric light bulb in a holder so that you can dangle the light bulb down.
2. Push the ends of two pieces of copper wire through a cork in a small bottle. Connect the ends of the copper wire inside the bottle with a stand of steel wool. Connect this model electric lamp model in a circuit with one or more dry cells, or lead cell accumulators, and a switch. Close the switch until the fine wire filament begins to glow. At first the heated iron wire produces light but soon the iron combines with the oxygen of the air inside the bottle and burns.
3. Examine a manufactured electric light bulb. It contains a mixture of argon and nitrogen, but no oxygen. It has a tungsten carbide wire filament that glows without burning when heated to a high temperature. The argon restrains the blackening of the inside of the bulb by deposition of tungsten vapour. Fluorescent lamps containing mercury vapour or neon gas are much more energy efficient.
4. Examine an electric light bulb for any greying of the inner surface. The grey layer comes from the evaporation of the tungsten filament that becomes thin with time. Other reactive metals, e.g. tantalum and titanium, may be placed near the filament to to attract the tungsten vapour away from the glass bulb. At the time of burnout, an electric light bulb may have dimmed by 15%.
4.66 Electric current detector
See diagram 32.163.1: Electric current detector - Compass in a coil | See diagram 32.163.2: Plotting compass - Compass in a match box
Current electricity is electricity flowing as a current. It is a form of energy caused by charged particles, e.g. protons, electrons, accumulating dynamically as a current.
Wrap 50 to 60 turns of bell wire to form a coil around a container 8 cm in diameter. Remove the coil from the container and bind it with short pieces of wire or insulating tape. Mount the coil on a piece of cardboard. Attach a 16 mm plotting compass to a cork and fix it inside the vertical coil. Rotate the coil until it is in line with the compass needle. Connect a battery to the coil and note the deflexion of the compass needle. Reverse the connections, and note the deflexion of the compass needle again. Make a more sensitive instrument by putting a compass in the tray of a match box then winding the coil wire over the box.
4.137 Static electricity from rubbing
See diagram 31.137: Static electricity from rubbing
1. Static electricity is electricity not flowing as a current. It is a form of energy caused by charged particles, e.g. protons, electrons, accumulating statically.
Make circular pieces of paper with a hole puncher or make a pile of cork particles by filing or cutting a cork. Rub a plastic comb or plastic rule or plastic ball pen case with a woollen jumper or your dry hair, or rabbit fur or flannel or silk. Note which rubbing attracts the most circular pieces of paper or pieces of cork
2. Make a pile of finely divided cork particles by filing a cork. Cut up some thin paper into small pieces. Use very clean objects such as a plastic comb, a plastic pencil, a plastic fountain pen, a piece of wax, a rubber balloon, a glass or china dish and any other non-metallic objects you may find. Rub each of these things briskly with your dry hair or a piece of fur and then bring near the pile of cork particles. Rub again and bring near the pile of thin paper. Observe what happens. Repeat the experiment, rubbing each article in turn with a silk cloth. Repeat using a piece of flannel.
4.138 Attract water to a comb
1. Turn on a tap so that a thin continuous stream of water flows. Charge a comb by combing your hair several times. The friction between you hair and the comb cause excess electrons on the comb so it becomes negatively charged. Hold the comb near the stream of water where it comes out of the tap. The comb attracts the water because of the negative electrical charges on the comb attract positive charges in the water molecules. The charges on the water molecules inside the water stream neutralize each other but the charges on the surface of the stream opposite the comb cannot be neutralized so the side of the stream opposite the comb is attracted to the comb pulling the rest of the stream along with it.
2. Repeat the experiment using "Golden Syrup" or treacle or thin honey instead of water.
4.139 Balloon stays in place
Blow up a toy balloon and rub it briskly with a piece of fur. Place it high up against the wall. Observe that it stays where you placed it. repeat the experiment by rubbing the balloon with your hair.
4.140 Repulsing balloons
Blow up two balloons and tie with strings one metre long. Rub each balloon with fur. Hold the strings together and note how they repel. Put your hand between them and note what happens. Bring one balloon near your face. Repeat, using three balloons.
4.141 Newspaper stays on the wall
See diagram 31.141: The newspaper stays on the wall
Spread out a sheet of newspaper and press it smoothly against a wall on a dry day. Stroke the newspaper with a pencil or your hand all over its surface several times. Pull up one corner of the paper and then let it go. Notice how it is attracted back to the wall. If the air is very dry, hear the crackle of the static charges. If you hold the charged paper near your cheek, you may receive a tickling feeling. Repeat the experiment by rubbing the paper with wool, fur, nylon, plastic or celluloid.
4.141.1 Coin stays on the cupboard door
This experiment can work on unpainted wood but it works best on waxed surfaces. Rub a coin up and down on the cupboard door with a brisk action. Remove you hand and the coin stays on the vertical door. The rubbing action causes increased pressure and friction so that the air under the coin becomes hotter and expands. Some of this hotter air leaks out from under the coin as it moves across the surface of the cupboard door. When you stop rubbing, the remaining air under the coin cools and contracts causing a partial vacuum. So the atmospheric pressure on the outside of the coin is greater than the pressure of air under the coin and the coin stays pressed against the cupboard door.
4.142 Static electricity detector
See diagram 31.142: A static electricity detector
Cut a strip 2 cm by 10 cm from thin cardboard. Fold it in half lengthways and balance it on a pencil point. The pencil point should indent but not perforate the paper, so that the paper can turn easily. Charge a comb by rubbing on hair or wool and hold it near one end of this detector.
4.143 Pith ball indicator
Use the white pith from inside a plant stem. Dry the pith thoroughly and then press it tightly into small balls 5 mm in diameter. Coat the pith balls with aluminium powder in egg white, colloidal graphite or metal paint. Attach each pith ball to a silk thread or fishing line 15 cm in length. Bring objects rubbed with silk, fur or flannel near the pith ball and note how it behaves. This equipment is an electroscope. In place of pith balls, use grains of puffed wheat, puffed rice, expanded polystyrene, Styrofoam balls, ping-pong balls, or any light object.
4.144.0 Electroscope, metal foil ball electroscope, metal foil ball electroscope
See diagram 31.144: Metal foil ball electroscope
An electroscope is used to detect electricity in the air by ionization of air molecules.
1. Metal foil ball electroscope
Roll metal aluminium foil from a chocolate packet into a ball. Use adhesive tape to attach a piece of thread to the ball. Tie the free end of the thread to a plastic ball pen sleeve. Place the ball pen sleeve across the mouth of a container so that the ball of foil hangs in the centre of the container, clear of the sides. Bring a charged body near the metal ball. At first the charged body attracts the ball then the ball jumps away. Rub another ball pen sleeve on a plastic protractor. Hold the pen near the ball and let it take a charge. Bring the protractor near the charged ball.
2. Metal leaf electroscope
Use the equipment above but instead of a ball of metal foil attached to a thread, hang a folded piece of tissue paper or strip of aluminium foil over the ball pen sleeve so that they do not touch the sides of the container. Bring a charged body near the ball pen sleeve. The leaves of the paper fly apart because they have the same kind of charge.
4.144.1 Gold leaf electroscope
See diagram 31.5.3: Gold leaf electroscope
The gold leaf electroscope is used for detecting and measuring electric charges. It consists of two gold leaves attached to a brass rod in a glass vessel. A metal cap is attached to the end of the rod. When the leaves have charges of the same sign they repel each another like an inverted V and separate more widely if the charge is increased or fall together if the charge is decreased. The gold leaves may be charged by induction or by contact. Suppose that they are charged negatively. The sign of the charge on any charged body may be found by bringing it up to the terminal of the electroscope. If a positively charged body is held close to the terminal, electrons from the leaves will be attracted up to the terminal by the positive charge, and the charge on the leaves will be decreased and they will fall together. If a negatively charged body is held close to the terminal, electrons will leave the terminal and go down to the gold leaves to increase their charges and so the leaves will separate more than before. So if the gold leaves are charged together negatively, they fall together for a positively charged body, and separate for a negatively charged body.
To use a negatively charged body to charge the gold leaf electroscope positively,  place the negatively charged body near the terminal so that electrons will flow down to the gold leaves, leaving the terminal positively charged. When the rod is earthed, grounded by touching with the finger, electrons flow from the leaves to the earth, leaving the leaves neutral. When the earth connection is broken, and the charging body then removed, the positive charge from the terminal distributes over the terminal and leaves, leaving the electroscope with a net charge of opposite polarity to the charged body
To use a negatively charged body to charge the gold leaf electroscope negatively, place the negatively charged body on the terminal to make direct contact between the terminal and charged body
An electroscope used for measuring electric charges may have only one leaf. The case is metal and is also charged. The movement of the leaf indicating the magnitude of the charge or potential measured.
4.146 Two kinds of static charge
See diagram 31.146A: Positive and negative charges attract each another. Negative charges repel each another. | See diagram 31.146B: Use an uncharged pith ball electroscope. | See diagram 31.146C: Use a charged pith ball electroscope.
The basic observations of electrostatics are as follows:
Observation 1. Rub a plastic comb with fur. The plastic comb becomes -ve and the fur becomes +ve.
Observation 2. Rub a glass rod with silk. The glass rod becomes +ve and silk becomes -ve.
1. Like static charges repel each other and unlike charges attract each other. Make a turntable by driving a long nail through a wood base. Push a test-tube into a hole made in a large flat cork. File the end of the nail to a sharp point and invert the test-tube over it. Set pins in the top surface of the cork, they brace the objects you put on the turntable. Use two test-tubes or glass rods, a piece of silk, two plastic combs, an ebonite rod, some wool, and a piece of fur or flannel. Rub a comb with fur and set it on the turntable. Rub the other comb with fur and bring it near the comb on the turntable.
2. Rub a glass rod with silk and put it on the turntable. Again rub a comb with fur and bring it near the glass rod. Repeat until you are sure of your observations. When you rub the comb with fur, the plastic takes a negative charge of electricity and the fur takes a positive charge. When you rub glass with silk, the glass takes a positive charge and the silk a negative charge.
3. Rub an ebonite rod with a piece of wool and bring the rod near an uncharged pith ball electroscope. Note that the pith ball is first attracted and then repelled.
4. Rub a glass rod with a piece of silk and bring the rod near an uncharged pith ball electroscope. The pith ball is at first attracted to the glass rod and then repelled.
5. Charge a pith ball negatively by touching it with an ebonite rod rubbed with wool. When you bring a negatively charged plastic comb near the negatively charged pith ball, they repel each other. When you bring a positively charged glass near the negatively charged pith ball, they attract each other.
4.147 Pith ball indicator
Use the white pith from inside a plant stem. Dry the pith thoroughly and then press it tightly into small balls 5 mm in diameter. Coat the pith balls with aluminium powder in egg white, colloidal graphite or metal paint. Attach each pith ball to a silk thread or fishing line 15 cm in length. Bring objects rubbed with silk, fur or flannel near the pith ball and note how it behaves. This equipment is an . In place of pith balls, use grains of puffed wheat, puffed rice, expanded polystyrene, Styrofoam balls, ping-pong balls, or any light object.
4.159 Resistors in series and parallel
See diagram 32.2.2.1: Resistors in series and parallel
Connect one, two and three identical bulbs in series. Record the brightness of the bulbs. When bulbs are connected in series, the total voltage is divided between them, e.g. if three bulbs are connected in series to a 3 volt battery, each bulb receives 1 volt. Connect one one, two and three bulbs in parallel. Record the brightness of the bulbs. When lamps are connected in parallel, each bulb receives the full voltage of the supply.