Sec 3 Physics Thermal Properties of Matter topical questions

Define internal energy, and state what happens to the two parts of it when a body is warmed without changing state.

A 0.30 kg aluminium block (c = 900 J/(kg·°C)) gains 4050 J of energy.

1. (a)Calculate its temperature rise.[2]
2. (b)A second block of the same metal gains the same energy but rises only half as much. State its mass.[1]

State three differences between boiling and evaporation.

A 0.75 kg steel drill bit at 20 °C is placed in boiling water at 100 °C until it reaches 100 °C. (Specific heat capacity of steel = 450 J/(kg·°C).)

1. (a)Calculate the energy transferred to the drill bit.[2]
2. (b)The bit is then returned to work and cools back to 20 °C. State the energy transferred away and the direction of transfer.[2]
3. (c)Why does the bit never warm above 100 °C in the water?[1]

A 2.0 kW hot plate supplies energy to 0.80 kg of a liquid whose temperature rises from 18 °C to 48 °C in 4 minutes 0 seconds.

1. (a)Calculate the energy supplied by the hot plate.[2]
2. (b)Calculate the specific heat capacity of the liquid, assuming no losses.[2]
3. (c)State one loss that would make the true specific heat capacity different from your answer.[2]

A bowl of soup at 85 °C stands in a 25 °C room. Its temperature is recorded as it cools.

1. (a)Sketch or describe the shape of the cooling curve.[2]
2. (b)Explain why the curve is steep at first and gentler later.[3]
3. (c)Estimate the room temperature from the trend.[1]

An ice cube of mass 0.040 kg at 0 °C is dropped into a drink and melts completely. (Specific latent heat of fusion of ice = 3.34 × 10⁵ J/kg.)

1. (a)Calculate the energy the ice takes from the drink to melt.[2]
2. (b)The melted ice then warms to 10 °C (c of water = 4200 J/(kg·°C)). Calculate that extra energy.[2]
3. (c)State the total energy removed from the drink.[1]

A 0.30 kg sample of molten metal is poured into a mould and cools. The temperature holds at 660 °C for 90 s while it solidifies, then falls to 40 °C over the next 5.0 minutes. (Specific latent heat of fusion of the metal = 3.9 × 10⁵ J/kg; specific heat capacity of the solid metal = 900 J/(kg·°C).)

1. (a)Explain why the temperature holds at 660 °C.[2]
2. (b)Calculate the energy released during solidification.[2]
3. (c)Calculate the rate of energy loss to the surroundings during the plateau.[2]
4. (d)Calculate the energy released as the solid cools from 660 °C to 40 °C.[2]

A kettle of 1.8 kg water at 22 °C is switched on (2.4 kW) and left until all the water just boils away. (c of water = 4200 J/(kg·°C); specific latent heat of vaporisation = 2.26 × 10⁶ J/kg. Boiling point 100 °C.)

1. (a)Calculate the energy to bring the water to 100 °C.[2]
2. (b)Calculate the energy to boil it all away.[2]
3. (c)Calculate the total time the kettle runs, assuming no losses.[3]
4. (d)State one reason the real time is longer.[1]

A 0.12 kg copper block (c = 380 J/(kg·°C)) is heated in a Bunsen flame delivering energy at 150 W for exactly 2.0 minutes. The block warms from 18 °C to 95 °C.

1. (a)Calculate the energy supplied by the flame.[2]
2. (b)Calculate the energy actually gained by the block.[2]
3. (c)Calculate the percentage of the supplied energy that was gained by the block, and state the destination of the rest.[3]

A student performs the mixing experiment: a 0.80 kg block of unknown metal at 100 °C is dropped into 0.50 kg of water at 18 °C inside an insulated cup. The final temperature is 27 °C. (c of water = 4200 J/(kg·°C).)

1. (a)Calculate the energy gained by the water.[2]
2. (b)Assuming no losses, calculate the specific heat capacity of the metal.[3]
3. (c)The value is higher than the data book for that metal. Suggest one experimental reason.[2]
4. (d)State the direction of energy flow at the instant of mixing, using temperatures.[1]

A cooling curve for 0.20 kg of a substance shows: temperature falling from 85 °C to 48 °C in 60 s; a flat plateau at 48 °C lasting 150 s; then falling from 48 °C to 20 °C in 200 s. (Specific latent heat of fusion = 2.1 × 10⁵ J/kg; specific heat capacity of the solid = 1100 J/(kg·°C).)

1. (a)State the freezing point.[1]
2. (b)Calculate the energy released during the plateau and the average rate of loss.[3]
3. (c)Calculate the energy released while the solid cools from 48 °C to 20 °C, and the rate.[3]
4. (d)Compare the two rates and suggest one reason they differ.[1]