Heat Transfer

Question 1

What is heat

Answer 1

Heat is a form of energy and is therefore measured in joules.

Question 2

What is temperature

Answer 2

It is a measure of how hot or how cold an object is. Usually measured using a thermometer usually in degrees Celsius.

Question 3

How can heat energy be transported

Answer 3

Conduction, convection and radiation

Question 4

Define conduction

Answer 4

The transfer of heat from molecule to adjacent molecule by vibrations

Question 5

Define convection

Answer 5

The transfer of heat through a liquid or gas by the motion of molecules themselves

Question 6

What is radiation

Answer 6

Radiation is the transfer of energy by electromagnetic waves, usually infrared waves

Question 7

How does conduction work in metals

Answer 7

In metals free electrons move freely throughout the solid structure, free electrons will absorb heat causing them to move much faster. These fast free electrons collide with the metal’s atoms, these collisions cause the atoms to vibrate faster than before.

Question 8

How does conduction work in non-metals

Answer 8

Atoms will absorb heat directly this causes the atoms to vibrate faster than before, these vibrations pass from atom to atom through the solid structure, this process is much slower than electron conduction in metals

Question 9

How does convection work

Answer 9

Convection only occurs in gasses and liquids. Convection occurs when the fastest moving particles in a hot region of a gas or liquid move to a cool region, taking their heat energy with them.

Question 10

What does heat cause

Answer 10

Expansion and therefore a decrease in density

Question 11

Why are non-metals good insulators

Answer 11

Have no free electrons so take longer to conduct heat compared to metals

Question 12

Why are metals good conductors

Answer 12

They have free electrons which move easily and can carry heat energy

Question 13

Why is the best insulator a vacuum

Answer 13

There is no material present to conduct the heat.

Question 14

What is the next best option for an insulator excluding a vacuum

Answer 14

Pockets of trapped air, eg a duvet, spray foam or a coffee cup

Question 15

What causes convection currents?

Answer 15

Molecules gain kinetic energy, this extra energy causes the molecules to vibrate with greater amplitude. This warm water then expands. The density of the warm water is less than that of the cold water. The warm water rises and the cooler water flows downwards replacing it. This cycle repeats

Question 16

What do all objects do (heat radiation)

Answer 16

All objects radiate heat through infrared waves.

Question 17

Explain radiation

Answer 17

Radiation is a method of heat transfer that takes place without the need for any particles, so it can transfer heat even in a vacuum. The hotter an object is the more radiation it emits.

Question 18

Which colours are best reflectors

Answer 18

Bright shiny objects

Question 19

Which coloured objects are the best radiators (emitters) and absorbers of heat

Answer 19

Dark, Matt

Question 20

What are the main sources of heat loss in a house

Answer 20

Conduction and convection, roof, outside walls, windows, doors and ground floors

Question 21

How can houses prevent heat loss

Answer 21

Super-insulation, heat recovery ventilation unit, triple glazed windows, foam insulation

Question 22

How does a thermos flask work

Answer 22

Double wall, vacuum between two walls, vacuum stops all heat transfer by conduction or convection through sides.
Walls facing the vacuum are silvered, shiny surfaces reduce heat transfer by radiation to a minimum.
Stopper made of plastic often filled with cork or foam to reduce heat transfer through it by conduction.