Specific latent heat

Figure 5 shows a plastic kettle.

The kettle is connected to the mains electricity supply.

What is the frequency of the UK mains electricity supply?

Tick () one box.

The cable that connects the kettle to the plug contains two insulated wires.

Draw one line from each wire to the colour of the insulation on the wire.

Use the Physics Equations Sheet to answer questions 04.3 and 04.4.

Write down the equation that links current (I), potential difference (V) and power (P).

The power of the heating element in the kettle is 2100 W.

The potential difference across the heating element is 230 V.

Calculate the current in the heating element.

Give your answer to 2 significant figures.

The kettle is designed to switch off when the water reaches boiling point.

Before the kettle switches off, 0.0080 kg of water changes state.

The energy transferred to change the state of the water is 18 000 J.

Calculate the specific latent heat of vaporisation of the water.

Use the Physics Equations Sheet.

Specific latent heat of vaporisation = J/kg

A different kettle is used to heat some water.

The useful output energy transferred to the water is 75 600 J.

The total input energy transferred by the kettle is 84 000 J.

Calculate the efficiency of the kettle.

Use the equation:

Explain one advantage of electrical appliances having a high efficiency.

A piece of steel is heated until it has all melted.

Calculate the change in thermal energy when the temperature of the piece of steel is increased by 50 °C.

mass of steel = 4.0 kg

specific heat capacity of steel = 420 J/kg °C

Use the equation:

change in thermal energy = mass × specific heat capacity × temperature change

The internal energy of the steel increases as the steel is heated.

What is meant by ‘internal energy of the steel’?

Tick (✓) one box.

Solid steel cannot be poured.

Which statement about the particles in a solid gives the reason why?

Tick (✓) one box.

Complete the sentence.

Choose the answer from the box.

Which diagram shows how the arrangement of particles changes when a solid melts and becomes a liquid?

Tick (✓) one box.

The density of steel decreases as it melts.

How does the spacing of the particles change as the steel melts?

Complete the sentence.

Choose the answer from the box.

Steel is a mixture of iron and a small amount of carbon.

Table 1 shows the mass of carbon in 1.0 kg of different types of steel.

A 4.0 kg piece of steel contains 18 grams of carbon.

Determine which type of steel the 4.0 kg piece is made from.

You should include a calculation in your answer.

The 4.0 kg piece of solid steel was heated until it reached its melting point.

The additional energy required to melt the piece of steel was 280 000 J.

Calculate the specific latent heat of fusion of the steel.

Use the Physics Equations Sheet.

Figure 6 shows a swimmer wearing a wetsuit.

The wetsuit helps to keep the swimmer warm.

A student wrapped a thermometer in a piece of wetsuit material and placed the thermometer in water containing ice.

Figure 7 shows the apparatus.

After 30 seconds in the water the temperature of the thermometer had decreased by 7.5 °C

Calculate the average decrease in temperature each second.

The student recorded the temperature of the thermometer after 30 seconds for four materials. Each piece of material was the same size and thickness.

In each test the starting temperature of the thermometer was 21.0 °C

Table 2 shows the results.

Complete Figure 8 using the data in Table 2.

You should:

• label the y-axis

• draw the bars for materials Y and Z.

Which material is the best thermal insulator?

Give a reason for your answer.

Tick (✓) one box.

The student tested a new material with a greater thermal conductivity than material Z.

The piece of new material was the same size and thickness as the piece of material Z.

What was the temperature of the thermometer after 30 seconds?

Tick (✓) one box.

During the investigation 0.0150 kg of the ice melted. The temperature of the water and ice did not change.

specific latent heat of fusion of ice = 334 000 J/kg

Calculate the energy needed to melt the ice.

Use the equation:

energy to melt the ice = mass × specific latent heat

The student wanted to determine the density of a wetsuit material.

The student measured the length of one side of a cube of wetsuit material with:

• a micrometer

• a ruler.

Table 3 shows the results.

Complete the sentence.

Choose the answer from the box.

The results show that compared to the ruler the micrometer has a higher

Use the Physics Equations Sheet to answer questions 04.7 and 04.8.

Write down the equation that links density (ρ), mass (m) and volume (V).

The student calculated the volume of the cube of wetsuit material to be 0.186 cm³

The density of the cube was 0.300 g/cm³

Calculate the mass of the cube.

Give your answer in grams.

An air source heat pump transfers energy from the air outside a building to increase the temperature of the air inside the building. Figure 13 shows an air source heat pump.

The compressor is connected to the mains electricity supply. The pipe in the heat pump contains a substance called coolant. In the evaporator, energy is transferred from the air outside the building to the liquid coolant. The temperature of the coolant increases and it evaporates.

Explain what happens to the internal energy of the coolant as its temperature increases.

What name is given to the energy needed to change the state of the liquid coolant?

What happens to the mass of the coolant as it evaporates and becomes a vapour? Tick (✓) one box.

The compressor increases the density and temperature of the coolant vapour inside the pipe. Explain why the pressure in the pipe increases.

The condenser transfers energy from the coolant to the air in the building. When the total energy input to the heat pump system is 1560 kJ the temperature of the air in the building increases from 11.6 °C to 22.1 °C. The efficiency of the heat pump system is 87.5%. The mass of the air inside the building is 125 kg. Calculate the specific heat capacity of the air in the building. Give your answer in standard form.

The air in the building gains 400 J for every 100 J of energy transferred from the mains electricity supply to the compressor. An advertisement claims that the heat pump system has an efficiency of 400%. Explain why the advertisement is not correct.

A scientist had a balloon which was filled with air.

Which statement describes how air particles move? Tick (✓) one box.

The temperature of the air was 19 °C The scientist dipped the balloon into liquid nitrogen. The temperature of the liquid nitrogen was −196 °C

Which thermometer could be used to measure the temperature of the liquid nitrogen? Tick (✓) one box.

The scientist wore special insulating gloves when putting the balloon into the liquid nitrogen. Suggest why.

When the balloon was put into liquid nitrogen the temperature of the air in the balloon decreased. Complete the sentences. Choose answers from the box. Each answer may be used once, more than once or not at all.

As the air in the balloon cooled down, the speed of the particles

The air in the balloon had a mass of 0.00320 kg The temperature of the air in the balloon decreased by 215 °C The change in thermal energy of the air in the balloon was 860 J Calculate the specific heat capacity of the air in the balloon. Use the Physics Equations Sheet.

The liquid nitrogen boiled. What happens to the temperature of nitrogen as it boils?

Tick (✓) one box.

The scientist recorded measurements to calculate the specific latent heat of vaporisation of nitrogen.

What is meant by vaporisation? Tick (✓) one box.

The mass of nitrogen that vaporised was 0.0072 kg 1440 J of energy was transferred to the nitrogen as it vaporised. Calculate the specific latent heat of vaporisation of nitrogen. Use the Physics Equations Sheet.

Figure 5 shows a wood-fired hot tub.

What type of fuel is wood? Tick (✓) one box.

Give two environmental effects of using wood as an energy resource.

Describe the change to the stores of energy of the wood, pipe and water as the water is heated.

The temperature of the water reaches 42 °C The temperature then stays constant even though the fire continues to burn. Explain why the temperature of the water stays constant.

Ice cream is made by cooling a mixture of liquid ingredients until they freeze.

Which statement describes the motion of the particles in solid ice cream? Tick (✓) one box.

How do the kinetic energy and the potential energy of the particles change as a liquid

Figure 6 shows a bowl used for making ice cream.

The walls of the bowl contain a liquid coolant. The bowl is cooled to –20 °C before the mixture is put in the bowl. The bowl causes the mixture to cool down and freeze.

Explain why the different thermal conductivities of metal and plastic are important in the design of the bowl.

The liquid coolant has a freezing point below –20 °C Explain one other property that the liquid coolant should have.

The initial temperature of the mixture was +20 °C. The mixture froze at –1.5 °C. A total of 165 kJ of internal energy was transferred from the mixture to cool and freeze it. specific heat capacity of the mixture = 3500 J/kg °C specific latent heat of fusion of the mixture = 255 000 J/kg

Calculate the mass of the mixture. Give your answer to 2 significant figures.

In an experiment, a beam of alpha particles was directed at a thin sheet of gold foil.

Most of the alpha particles passed straight through the gold foil.

Alpha particles which passed close to the nucleus of a gold atom did not pass straight through.

What happened to the alpha particles which passed close to the nucleus of a gold atom?

The results suggested that the diameter of the nucleus of a gold atom is of the 0 3. 2 diameter of the atom.

The diameter of a gold atom is 0.18 nm

Calculate the diameter of a gold nucleus in nm

Further experiments showed that gold nuclei are surrounded by electrons in different energy levels.

Figure 4 shows three of the energy levels around the nucleus of a gold atom.

The electron in energy level B absorbs electromagnetic radiation.

Which energy level will the electron be in after it has absorbed the electromagnetic radiation?

Tick (✓) one box.

Figure 5 shows how the temperature of a small sample of gold changes as it is heated from a solid to a liquid.

What is the melting point of the gold?

How many minutes did it take for all of the gold in the sample to change from solid to liquid?

What does the gradient of the graph in Figure 5 represent?

Tick (✓) one box.

A scientist cooled the air inside a container.

The temperature of the air changed from 20 °C to 0 °C

The volume of the container of air stayed the same.

Explain how the motion of the air molecules caused the pressure in the container to change as the temperature decreased.

The air contained water that froze at 0 ° C

The change in internal energy of the water as it froze was 0.70 kJ

The specific latent heat of fusion of water is 330 kJ/kg

Calculate the mass of ice produced.

Use the Physics Equations Sheet.

The air also contained oxygen, nitrogen and carbon dioxide.

Oxygen boils at –183 °C and freezes at –218 °C Nitrogen boils at –195 °C and freezes at –210 °C Carbon dioxide sublimates at –78 °C

The scientist continued to cool the air to a temperature of –190 °C

What is the state of each substance at –190 °C?

Tick (✓) one box for each row of the table.

The air also contained a small amount of argon.

As the temperature of the air decreased from 20 °C to –190 °C the argon changed from a gas to a liquid to a solid.

Explain the changes in the arrangement and movement of the particles of the argon as the temperature of the air decreased.

A scientist cooled the air inside a container.

The temperature of the air changed from 20 °C to 0 °C The volume of the container of air stayed the same. Explain how the motion of the air molecules caused the pressure in the container to change as the temperature decreased.

The air contained water that froze at 0 ° C The change in internal energy of the water as it froze was 0.70 kJ The specific latent heat of fusion of water is 330 kJ/kg Calculate the mass of ice produced. Use the Physics Equations Sheet.

The air also contained oxygen, nitrogen and carbon dioxide. Oxygen boils at –183 °C and freezes at –218 °C Nitrogen boils at –195 °C and freezes at –210 °C Carbon dioxide sublimates at –78 °C The scientist continued to cool the air to a temperature of –190 °C

What is the state of each substance at –190 °C?

Tick (✓) one box for each row of the table.

The air also contained a small amount of argon. As the temperature of the air decreased from 20 °C to –190 °C the argon changed from a gas to a liquid to a solid. Explain the changes in the arrangement and movement of the particles of the argon as the temperature of the air decreased.

Some ceiling lights in the home are connected to the mains by a two-core cable.

Figure 6 shows a ceiling light.

Suggest why some ceiling lights do not have an earth wire.

Write down the equation that links charge flow, current and time.

There is a current of 2.95 A in one of the copper wires for 60 seconds.

Calculate the charge flow through the wire.

Use your equation from question 04.2

Figure 7 shows a current potential difference graph for a piece of copper wire.

Draw another line on Figure 7 for a wire with a different resistance.

Some fuses have a thin piece of copper that melts if the current is too large.

Draw the circuit symbol for a fuse.

Describe how the movement of the copper particles in the wire changes when copper melts.

Old copper wires are melted when they are recycled.

Calculate the energy needed to melt 500 kg of copper at its melting point.

Specific latent heat of fusion of copper = 200 kJ/kg

Use the Physics Equations Sheet.