Sec 3 Physics Thermal Processes topical questions

Name the main thermal transfer process in each case.

1. (a)A metal gate feels hot along its whole length in the Sun.[1]
2. (b)Soup swirls as it warms in a pot.[1]
3. (c)Your face feels a bonfire from 2 m away.[1]
4. (d)The Sun warms a swimming pool.[1]

State what is meant by thermal equilibrium.

Explain why metals conduct thermal energy better than wood.

A student heats a beaker of water with a small blue flame placed under the centre of its base. A crystal of purple dye dropped in shows the circulation.

1. (a)Describe the convection current, explaining why the warmed water rises.[3]
2. (b)State what happens to the dye pattern if the flame is moved to heat the TOP of the beaker, with a reason.[2]
3. (c)Name the transfer process that would still carry a little energy downward in (b).[1]

A vacuum flask of hot tea stands on a table. Its features: glass walls separated by a vacuum, silvered surfaces, a cork stopper, and an outer plastic case.

1. (a)Explain how the vacuum reduces thermal energy transfer.[2]
2. (b)Explain the purpose of the silvered surfaces.[2]
3. (c)State which transfer process the stopper mainly reduces.[1]
4. (d)Explain why the same flask keeps iced water cold.[2]

Two identical mugs of hot water stand side by side: one dull black, one shiny white. A thermocouple in each records the cooling.

1. (a)State which mug cools faster and identify the process responsible.[2]
2. (b)The mugs are emptied, cooled, and placed equally near a heater. State which warms faster and why.[2]
3. (c)State two ways to reduce the cooling of the black mug without changing its surface.[2]

A room heater (radiator) warms a cold room. Describe how each transfer process contributes to warming a student sitting across the room.

1. (a)Describe the direct effect on the student.[1]
2. (b)Describe the convection loop that forms.[3]
3. (c)Explain why the room does not warm equally fast near the floor.[2]

A house in a temperate climate has: tiled floors, single-glazed metal-framed windows, an uninsulated roof, and dark walls. Winter heating bills are high.

1. (a)Identify the main transfer route losing energy through the roof, and one way to reduce it.[2]
2. (b)Explain why metal window frames increase the heat loss.[2]
3. (c)Explain how double glazing reduces loss through windows.[2]
4. (d)The dark walls absorb more sunshine. Suggest why this does not offset the winter losses.[2]

A pan of soup simmers on a gas hob. The soup at the bottom is 95 °C; the soup at the top is 80 °C.

1. (a)Describe the convection currents in the soup.[3]
2. (b)Explain why a metal spoon left in the pot has a hot bowl but a comfortably warm handle.[2]
3. (c)The cook covers the pot with a glass lid. State two effects of the lid on the transfer processes.[2]

Two identical solid copper blocks sit side by side. Block A is at 80 °C; block B is at 20 °C. They are pushed into contact.

1. (a)Describe, at the particle level, what happens in the contact region during the first minute.[3]
2. (b)State and explain the final temperature (ignore losses), and name the condition reached.[3]
3. (c)Explain why the blocks reach this state faster than two identical wooden blocks would.[2]

A solar water panel on a roof has a blackened copper absorber plate with water pipes bonded to its back, under a glass cover, with the whole box insulated underneath.

1. (a)Explain why the plate is blackened and made of copper.[2]
2. (b)Explain the purpose of the glass cover.[3]
3. (c)Explain the insulation beneath the plate.[1]
4. (d)Explain why water, not air, is pumped through the pipes.[2]

A student measures that a bare copper rod conducts heat 400 times better than the same-sized rod of glass. She fixes identical wax coins 5 cm from a flame-end on both rods and lights the flame.

1. (a)Estimate, using the conduction ratio, the time ratio for the coins to fall, and state which falls first.[2]
2. (b)Explain the particle-level difference that produces the ratio.[3]
3. (c)The glass rod cracks shortly after heating begins. Suggest why.[2]