Topic 6 Practice Paper: Thermal physics — question paper

Section A: Multiple-choice questions[10 marks]

Choose one answer for each question. Each question is worth 1 mark.

1. 1

   Which row describes the particles of a gas correctly?

   	Separation	Motion
   A	touching	vibrating about fixed points
   B	far apart	fast and random
   C	touching	sliding past one another
   D	far apart	vibrating about fixed points
2. 2

   Absolute zero is the temperature at which

   1. Awater freezes
   2. Bparticles have the least kinetic energy they can have
   3. Cgas pressure reaches a maximum
   4. Dall particles stop existing
   ( )
3. 3

   A fixed mass of gas is heated in a sealed, rigid container. The pressure rises because the particles

   1. Aexpand
   2. Bbecome smaller and faster
   3. Chit the walls harder and more often
   4. Drepel each other more strongly
   ( )
4. 4

   The temperature of a laboratory is 293 K. In degrees Celsius this is

   1. A566 °C
   2. B273 °C
   3. C293 °C
   4. D20 °C
   ( )
5. 5

   At constant temperature, a gas originally at 150 kPa and 200 cm³ is squeezed down to 60 cm³. Its new pressure is

   1. A500 kPa
   2. B375 kPa
   3. C60 kPa
   4. D45 kPa
   ( )
6. 6

   For the same temperature rise, the correct order of expansion from least to most is

   1. Agas, liquid, solid
   2. Bsolid, liquid, gas
   3. Cliquid, solid, gas
   4. Dsolid, gas, liquid
   ( )
7. 7

   How much energy raises 0.50 kg of water (c = 4200 J/(kg °C)) from 25 °C to 45 °C?

   1. A52 500 J
   2. B105 000 J
   3. C42 000 J
   4. D2100 J
   ( )
8. 8

   A wet towel dries fastest on a hot, windy day because evaporation increases with

   1. Ahigher temperature and more air movement over the surface
   2. Blower surface area and lower temperature
   3. Chigher humidity and smaller surface area
   4. Dlower temperature but higher surface area
   ( )
9. 9

   Thermal energy reaches Earth from the Sun mainly by

   1. Aconduction through space
   2. Bconvection currents in space
   3. Cevaporation of the Sun
   4. Dinfrared radiation
   ( )
10. 10

    A car cooling system uses water around the engine. The main reason water is chosen is its

    1. Alow boiling point
    2. Bhigh specific heat capacity, so it carries a lot of energy per degree of rise
    3. Chigh density, so it flows downwards
    4. Dpoor conduction, which insulates the engine
    ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided.

1. 11

   A student observes smoke particles in a smoke cell under a microscope. The specks of smoke are seen to move in small, random jerks.

   1. (a)

      Name this observation.

      [1]
   2. (b)

      Explain what causes the random jerking.

      [2]
   3. (c)

      State what this observation is evidence for.

      [1]
   4. (d)

      The specks are much larger than the molecules hitting them. State the correct term for the specks.

      [1]
2. 12

   A 2.5 kg block of aluminium (specific heat capacity 900 J/(kg °C)) is heated by a 42 W electric heater for 10 minutes. Assume all the electrical energy enters the block.

   1. (a)

      Calculate the energy delivered by the heater.

      [2]
   2. (b)

      Calculate the temperature rise of the block.

      [2]
   3. (c)

      In practice the measured rise is smaller. State the most likely reason.

      [2]
3. 13

   A sealed metal can of air sits in a warm room. The can is placed in a refrigerator and the air inside cools from 27 °C to 12 °C. The can’s volume cannot change.

   1. (a)

      Convert both temperatures into kelvin.

      [1]
   2. (b)

      Explain, in terms of particles, why the pressure inside the can falls.

      [2]
   3. (c)

      State what would eventually happen to the pressure if the air could be cooled towards absolute zero.

      [1]
4. 14

   A cup of hot tea stands on a table. It has a dull black metal spoon and a shiny metal lid resting beside it. The tea cools by all three transfer methods.

   1. (a)

      Describe how convection carries energy from the tea into the surrounding air.

      [2]
   2. (b)

      The shiny lid is placed over the cup. State and explain its effect on energy transfer by radiation.

      [2]
   3. (c)

      Explain why the dull black spoon would reach the temperature of the tea faster than a shiny silver one.

      [1]