Mechanism of heat transfer revision

Question 1

describe heat transfer by conduction

Answer 1

Thermal energy transfers between two objects in contact. Energy transfers from the hotter, faster moving particles of one object to the colder, slower moving particles of the other object, by colliding with them.

Question 2

What are poor conductors called

Answer 2

Insulators

Question 3

What substances make good conductors and why

Answer 3

Metals, because they have free electrons which help to carry and transfer the heat energy

Question 4

An experiment to test which materials make the best conductors

Answer 4

Put and ice cube on each of these materials, and whichever material the ice melts faster on is the better conductor of thermal energy

Question 5

Why does conduction not happen in a vacuum

Answer 5

There are no particles in a vacuum, and conduction is heat transfer, through the movement and collision of paricles

Question 6

Examples of poor conductors

Answer 6

wood, rubber, glass, sand

Question 7

How convection works

Answer 7

As water is heated, the particles gain more energy, moving faster and spreading out. This means the liquid expands and becomes less dense. This section of the liquid rises, displacing the colder water which sinks below. The cold water is then heated and the cycle repeats.

Question 8

Why do convection currents not happen in solids

Answer 8

For convection to occur, the substance must be free to move around, and the density should be able to change easily, which liquids and gases can do but solids can’t.

Question 9

Why convection currents don’t happen in a vacuum

Answer 9

Convection requires the movement of particles, and in a vacuum no particles are present

Question 10

How convection is used to heat a room

Answer 10

Convection is used in the radiator, as well as heating the air above it which rises, cools and sinks, is heated again. This happens again and again until all the air in the room is warm.

Question 11

Explain sea breezes in terms of convection

Answer 11

The air above land heats faster than air above the sea due to different specific heat capacities. The air above the land, heats, expands and rises, so the cool air above the sea flows in to fill in the empty space, where the air above the land had previously been.

Question 12

Explain radiation

Answer 12

The transfer of thermal energy by infrared waves, a type of electromagnetic radiation

Question 13

What kind of surfaces are good absorbers and emitters

Answer 13

Black, matte surfaces

Question 14

What surfaces are good reflectors

Answer 14

Light, shiny surfaces

Question 15

How do the colour of stars change with temp

Answer 15

Hottest stars appear blue, coolest appears red

Question 16

How to reduce conduction

Answer 16

Use insulators, e.g. rubber, or using a vacuum

Question 17

How do you reduce convection

Answer 17

By trapping air so that convection currents aren’t formed

Question 18

How to reduce radiation

Answer 18

Use light shiny surfaces to reduce emission. Using these light shiny surfaces to reflect radiation back to body we’re trying to keep warm.