Conduction, convection & radiation

A student does an experiment to investigate energy transfer by conduction.

The student plans to use the piece of apparatus shown in the photograph.

When the apparatus is placed in hot water, energy is transferred from the bottom of the bar to the top of the bar. The temperature-sensitive strip on each bar changes colour as the temperature of the bar changes.

The time taken for the colour change to reach the top of the bar can be used to compare how effective each metal is at transferring energy by conduction.

Give three control variables in the student’s investigation.

The student has this equipment.

• beaker

• hot water

• stopclock

• clamp and clamp stand

Design a method the student could use to compare the effectiveness of the metals at transferring energy by conduction.

You may draw a diagram to help your answer.

The table shows the results of the student’s investigation.

Plot a bar chart of the student’s results.

Deduce which metal is the most effective at transferring energy by conduction.

The photograph shows a cup that is designed to keep a drink hot.

The inside surface of the cup is shiny and silver‑coloured.

Explain how the shiny silver‑coloured surface helps to keep a drink hot.

Explain why a drink in the cup will stay hot for longer when the lid is placed on the cup.

A student investigates how the temperature of a drink in the cup varies with time.

This is the student’s method.

• pour some hot water into the cup and place the lid on the cup

• wait for the water to cool to 80C and then start a stopwatch

• measure the temperature of the water in the cup every 10 minutes

The graph shows the student’s results.

On the graph, draw a tangent to the curve when the temperature is 40C.

Calculate the gradient of the tangent to find the rate of temperature change of the water when the temperature is 40C.

Give your answer in C / minute.

rate of temperature change =_........ °C / minute

The student is working in a laboratory with a room temperature of 20C.

Draw a line on the graph to show how the temperature of the water in the cup would change if there was no lid on the cup.

A student investigates energy transfer by conduction in different metals.

The student uses wax to attach one coin to each of four different metal rods, and connects the rods to a heater.

When the heater is on, energy is transferred through the metal rods. This melts the wax and causes the coins to fall.

The diagram shows the student’s equipment viewed from above.

This is the student’s method.

Step 1 switch on the heater and start a stopwatch

Step 2 record the time taken for the coin to fall from each metal rod

Give the independent variable in this investigation.

Give the dependent variable in this investigation.

A teacher tells the student that their investigation is not valid (a fair test).

Give two ways to improve the validity of the student’s investigation.

The student improves the validity of their investigation.

Describe what the student should do to improve the reliability of their results.

The table gives the student’s results.

Plot a bar chart of the results on the grid.

State why a bar chart is a better choice than a line graph for this investigation.

The photograph shows infrared heating lamps being used to harden fresh paint on

Give a harmful effect of infrared waves.

The heating lamps produce visible light waves in addition to infrared waves.

Give two similar properties of visible light waves and infrared waves.

Give two differences between the properties of visible light waves and infrared waves.

The infrared heating lamps are placed 1.5 m from the car.

Calculate the time taken for infrared waves emitted from a lamp to reach the car.

[for infrared waves, speed = 3.0 × 10⁸m/s]

Paint takes less time to harden when it absorbs more energy from infrared radiation.

A technician observes that white paint takes more time to harden than black paint.

Explain this observation.

This question is about the Sun.

The table shows the different stages in the evolution of stars of different masses.

Complete the table by adding ticks () to show which stages of evolution occur in the life cycle of the Sun.

When viewed from Earth, the surface of the Sun is yellow in colour.

The surface of another star, Betelgeuse, is red in colour.

Explain the difference between the Sun and Betelgeuse, based on the different colours of their surfaces.

The Sun transfers energy to the Earth by radiation.

Give a reason why energy is not transferred from the Sun to the Earth by conduction or convection.

A satellite orbiting the Earth contains sensitive equipment that can be damaged if it gets too hot.

Explain which colour would be most appropriate for the outer surface of the satellite to protect the equipment.

Air is trapped in a boiling tube by sealing the boiling tube with a rubber bung.

The boiling tube is placed in a beaker containing hot water.

Energy is transferred from the thermal store of the water to the thermal store of the air in the boiling tube with an efficiency of 16%.

The air in the boiling tube gains 1800 J of energy during this process. This is defined as the useful energy transfer.

Calculate the amount of energy wasted during this process.

Give two ways that the apparatus could be modified to improve the efficiency of the energy transfer.

A student investigates how much infrared radiation is absorbed by different surfaces.

The photograph shows some of the equipment available to the student.

The student pours some water into each bottle.

Describe a method the student could use to investigate how the colour of the bottle affects the amount of infrared radiation absorbed by the bottle.

You may draw a diagram to help your answer.

The student plots a graph to show how the temperature of the water in each bottle varies with time.

Draw two curves to show the expected variation in temperature of the black bottle and the silver bottle during the investigation.

Label your curves with the colour of each bottle.

A student uses this apparatus to investigate energy transfer by conduction in metals.

This is the student’s method.

• attach four strips, each made of a different metal, to a wooden ring

• use wax to attach a metal tack to the end of each metal strip

• place the strips above a Bunsen burner

• light the Bunsen burner and start a stopwatch at the same time

• when enough energy has been transferred to the wax, it melts, causing the metal tack to fall

• record the time taken for each tack to fall

Explain how the wooden ring makes the apparatus safer for the student to use.

Describe how energy is transferred by conduction through the metal strips.

The bar chart shows the results of the student’s investigation.

Justify the use of a bar chart in this investigation.

State how the student could improve the reliability of their results.

The student concludes that iron is the best metal for transferring energy by conduction.

Evaluate the student’s conclusion.

The diagram shows some apparatus that can be used to determine the specific heat capacity of water.

Describe how a student could use this apparatus to determine the specific heat capacity of water.

Include details of any additional equipment needed in your answer.

The table shows the student’s results.

Use the student’s results to calculate the specific heat capacity of water.

specific heat capacity of water =_........ J / kg °C

Give two reasons why the energy from the heater is not all retained in the thermal store of the water.

In some countries, snow can fall and collect on the ground.

Diagram 1 shows that after the snow has fallen, the sky can be clear, leaving the snow directly exposed to the Sun.

Explain why the white snow will take a long time to melt, even though directly exposed to the Sun.

Diagram 2 shows a different piece of ground that has a metal drain cover.

If the snow lands on metal, the snow takes a shorter time to melt.

Explain why the snow melts in a shorter time on the metal drain cover.

Explain how a convection current above the snow increases the time taken for the snow to melt.

The driver of a racing car makes a pit stop during a race to change the tyres on the racing car.

The area where the tyres are changed is called the pit lane.

Before entering the pit lane, the speed of the car must decrease for safety reasons.

The mass of the racing car is 830 kg.

The maximum braking force is 41 000 N.

Show that the maximum deceleration of the racing car is approximately 50 m / s².

The racing car is travelling at an initial speed of 72 m / s.

Calculate the minimum distance needed to decrease the speed of the racing car from 72 m / s to 26 m / s.

The racing car slows down using its brakes.

The brakes work using friction.

The brakes become very hot when the racing car slows down.

Using ideas about energy, explain why the brakes become hot.

The tyres of the racing car also get very hot during a race.

A mechanic has to handle the hot tyres during the pit stop.

They wear protective gloves which have several layers of insulating materials.

Explain how the layers of insulating materials in the gloves reduce the risk of the mechanic burning their hands on the hot tyres.

The diagram shows a small computer in two difference cases, X and Y.

The electronic chip in the computer is hot when in use. Each case is designed to cool the computer chip.

Case X is made of white plastic and has a fan.

Case Y is made of black-painted aluminium metal and has no fan. There is a metal block that is in contact with the case and the chip.

Explain the main method of heat transfer from the chip to the surroundings for case X.

Explain the main method of heat transfer from the chip to the surroundings for case Y.

State the formula linking power, current and voltage.

The small computer operates at a voltage of 5.1 V with a current of 2.9 A.

Calculate the power of the small computer.

Give the unit.

A student pours a known volume of hot water into a metal container. They place the metal container into an insulated plastic cup containing an equal volume of cold water.

The student uses temperature probes to measure the temperatures of both the water in the metal container and the water in the plastic cup.

The hot water has an initial temperature of 70 °C and the cold water has an initial temperature of 5 °C.

On the axes, sketch how the temperature of the hot water and the temperature of the cold water vary with time.

Explain why the temperatures of the hot water and the cold water change.

You should refer to different types of thermal energy transfer in your answer.

Explain how placing a lid on the plastic cup would affect the results.

Hailstones are small pieces of ice that sometimes fall to the ground during storms.

Describe how to determine the density of a hailstone.

Assume that hailstones are spherical.

The mean volume of a hailstone is 1.1 cm³.

The mean mass of a hailstone is 0.94 g.

Calculate the mean density of a hailstone.

Give the unit.

Hailstones can be lifted to the top of clouds.

The diagram shows the movement of some hailstones in a cloud.

Suggest how hailstones are lifted to the top of the cloud by convection.

Funcube-1 is a satellite that was launched into orbit around the Earth.

The rocket carrying Funcube-1 burns fuel to accelerate upwards.

As the rocket burns fuel, the energy in its chemical store reduces and the energy in its kinetic store and gravitational store changes.

State how the kinetic store of the rocket changes as the rocket burns fuel.

State how the gravitational store of the rocket changes as the rocket burns fuel.

The rocket engine stops burning fuel.

The rocket continues to go further away from the surface of the Earth.

The table gives some statements about the rocket’s energy stores.

Funcube-1 goes into a circular orbit above the surface of the Earth.

State the name of the force responsible for keeping Funcube-1 in orbit.

Funcube-1 has an orbital radius of 7100 km and an orbital period of 5800 s.

Calculate the orbital speed, in km / s, of Funcube-1.

orbital speed =_........ km / s

Funcube-1 spins and is heated by the Sun.

The diagram shows two coloured metal bars attached to a face of Funcube-1.

The surface of one metal bar is dull and black.

The surface of the other metal bar is shiny and white.

Temperature probes measure the temperature of each metal bar.

Use ideas about thermal energy transfer to explain how the temperature of each metal bar changes as Funcube-1 spins.

The photograph shows a recyclable box designed for transporting cold food.

The box has these design features

• thick walls made from several layers of cardboard with air trapped between the layers

• a thick lid made from layers of cardboard

Cold food and ice packs are placed in the box.

Give a reason why there is a net transfer of energy from the outside of the box to the inside of the box during transportation in a hot country.

Explain how the box is designed to reduce energy transfer by conduction.

Explain how the box is designed to reduce energy transfer by convection.

A student suggests that painting the inner surfaces of the box a different colour would help to reduce the rate of energy transfer to the cold food.

Explain which colour the inner surfaces of the box should be painted.

A student investigates the rate of cooling of water in a beaker.

The student pours boiling water into a beaker and monitors the temperature of the water for a period of time.

The graph shows the student’s results.

The rate of cooling is represented by the gradient of the graph and is measured in C/s.

By drawing a tangent to the curve, determine the rate of cooling of the water at 70C.

The student repeats the investigation with the same beaker wrapped in woollen insulation.

Sketch another line on the graph to show the expected results when the beaker is wrapped in woollen insulation.

Assume that the starting temperature of the water is 82C.

A student uses a small iron nail and a beaker of water to estimate the temperature of a flame. The diagram shows some of the equipment used.

This is the student’s method

• place a thermometer into the beaker of water

• record the temperature of the water

• heat the nail in the flame for a long period of time

• quickly move the nail into the beaker of water

• record the highest temperature of the water

State a safety precaution the student should take.

While in the water, the thermal energy store of the nail decreases and the thermal energy store of the water increases until their temperatures are the same.

The energy lost from the nail is equal to the energy gained by the water.

The table shows the student’s results.

Show that the energy gained by the water is approximately 3000 J.

Calculate the temperature change of the nail.

Give a reason why the calculated temperature change of the nail is lower than the actual temperature change.

The diagram shows a building in a hot climate.

The air temperature is 35 °C and the underground temperature is 12 °C.

The external pipe is heated by the Sun. This causes cool air to enter the house through a tube in the ground.

How is energy transferred to the external pipe from the Sun?

Explain why air moves upwards through the external pipe.

Warm air enters the tube at point X.

Cool air leaves the tube at point Y.

Explain how the air is cooled as it travels through the tube.

The external pipe is painted to increase the air flow through the building.

Explain what colour of paint would give the greatest increase in air flow.

The photograph shows a large hurdle on an athletics track.

The bar of the hurdle is made of wood and is painted black and white.

The temperature of the hurdle increases when the Sun shines on it.

Explain which part of the bar reaches the highest temperature.

The air near the bar receives energy by heating.

Explain how a convection current is formed in the air near the bar.

The photographs show two different breeds of cat.

Cat X has no fur and light-coloured skin.

Cat Y has thick, black fur.

Both cats have the same body temperature and transfer energy to their surroundings when they are outside on a cold day.

Compare how cat X and cat Y transfer energy to their surroundings.

Refer to conduction, convection and radiation in your answer.

Energy is transferred from the Sun to the Earth.

Nuclear fusion happens in the Sun.

Which energy store of the Sun decreases during nuclear fusion?

How is energy transferred through space from the Sun to the Earth?

Solar panels use energy from the Sun to heat water.

The total area of the solar panels is 15 m².

Each 1.0 m² of the solar panels receives 1000 J of energy per second from the Sun.

Show that the total energy transferred to the solar panels in 2 hours is about 100 MJ.

A mass of 1100 kg of cold water is in the solar panels at an initial temperature of 20C.

Calculate the final temperature of this water after it has been heated by the Sun for 2 hours.

[specific heat capacity of water = 4200 J/kg C]

final temperature _........ C

Give a reason why the actual final temperature of the water will be lower than the calculated value.

The Parker Solar Probe is a spacecraft that was launched in 2018 on a mission to explore the Sun.

The spacecraft is partly covered in tiles.

These tiles are filled with a solid containing small pockets of trapped air.

The outer surface of the tiles is painted white.

These tiles protect the electric circuits in the spacecraft from extreme temperatures.

The diagram shows one of these tiles in cross-section.

Explain why the outer surface of the tile is painted white.

Explain how the small pockets of trapped air help to reduce thermal energy transfer from the outer surface to the inner surface of the tile.

The electric circuits inside the spacecraft are cooled by 4.5 kg of water.

The initial temperature of the water is 35^oC.

The thermal store of the water increases by 210 kJ.

Calculate the final temperature of the water.

[specific heat capacity of water 4200 J/kg^oC]

final temperature _........ ^oC

A teacher makes a hot drink.

He puts the drink in a cup designed to keep the drink hot.

The photograph and cross-section diagram both show the cup.

Explain how the design of the cup keeps the drink hot.

Refer to methods of energy transfer in your answer.

Photograph 1 shows an outdoor swimming pool.

The water in the swimming pool is heated by the Sun during the day.

State how energy is transferred from the Sun to the water.

State what happens to the average speed of the water molecules as the water is heated.

The water in the swimming pool cools down at night.

Suggest why the water cools down at night.

Photograph 2 shows the swimming pool with a plastic cover over the water.

Explain why the plastic cover reduces how much the water cools down at night.

A dog sits on a water‑filled bag to keep cool.

The table shows some data about the dog and the water in the bag.

The dog sits on the bag for 22 minutes.

Calculate the energy transferred from the dog to the water by heating in 22 minutes.

State an assumption you have made when calculating the energy transferred.

Calculate the temperature of the water after 22 minutes.

temperature =_........ C

Discuss why conduction is the main way that thermal energy is transferred from the dog to the water.