Thermal Energy

Question 1

What is conduction? Where does it occur? Simple definition and complex

Answer 1

Thermal conduction is the transfer of thermal energy through a substance by the vibration of the atoms within the substance. It occurs in solids. It is heating by direct contact

Question 2

How conduction works (steps)

Answer 2

1. Heat is transferred from the heat source to the particles in the metal
2. The kinetic energy of the particles increases.
3. They vibrate more
4. The free electrons in the metal also gain kinetic energy and move through the metal.
5. Energy is transferred when the particles collide

Question 3

How is conduction different in metals?

Answer 3

The process takes place much more rapidly because metals have free electrons that can move easily through the structure of the metal. This makes them good conductors.

Question 4

What is the definition of convection and where does it occur?

Answer 4

Convection is the transfer of thermal energy through fluids by the upward movement of warmer less dense region of fluid. It only occurs in liquids and gases

Question 5

Why can’t convection occur in solids?

Answer 5

Because the particles are too close together and convection requires particles that move freely and solids can’t because the particles are packed together.

Question 6

How convection occurs (steps)

Answer 6

1. Heat is transferred from the heat source to the particles in the fluid.
2. The kinetic energy of the particles increases
3. They move more and spread out.
4. The hot fluid is less dense and rises.
5. The cold fluid is more dense and sinks

Question 7

Convection currents (steps)

Answer 7

1. The heated water expands
2. The heated water becomes less dense than the colder water and so floats to the top.
3. Colder water sinks and is then heated too
4. At the top, the warm water starts to cool and becomes more dense and begins to sink.
5. The cold water rises
6. This keeps going on and on and is called a circulating current or convection currents.

Question 8

Definition of thermal radiation.

Answer 8

The transfer of energy by infrared waves

Question 9

What do all hot objects do in terms of radiation. The hotter the object…

Answer 9

All hot objects give off thermal radiation. The hotter the object, the more they emit.

Question 10

Can thermal radiation travel through a vacuum?

Answer 10

Thermal radiation is the only way in which heat can travel through a vacuum. This means that radiation doesn’t need particles to move and so can travel through a vacuum.

Question 11

How can we tell if an object is good at emitting and absorbing radiation?

Answer 11

The colour of the object

Question 12

Emitting meaning

Answer 12

Giving away

Question 13

How good is black (Matt) at absorbing and emitting radiation?

Answer 13

Good at absorbing

Good at emitting

Question 14

How good is white at absorbing and emitting radiation?

Answer 14

Poor at absorbing

Poor at emitting

Question 15

How good is silver at absorbing and emitting radiation?

Answer 15

Very poor at emitting

Very poor at absorbing

Question 16

How good is the colour dark at absorbing and emitting radiation?

Answer 16

Reasonable at absorbing

Reasonable at emitting

Question 17

How good is black (Matt) at reflecting?

Answer 17

Poor

Question 18

How good is white at reflecting?

Answer 18

Reasonable

Question 19

How good is silver at reflecting?

Answer 19

Good

Question 20

Which materials could you use to prevent conduction?

Answer 20

Fibre glass wool
Vacuum
Water

Question 21

How can you reduce convection currents from happening?

Answer 21

Use lids

e.g. Convection is reduced by using a lid as it prevents conduction currents in the air by trapping the air.

Question 22

How does surface area link to radiation?

Answer 22

The larger the surface area of the object, the faster heat is transferred by radiation

Question 23

How is conduction reduced?

Answer 23

If a vacuum is used, there is no particles and conduction can only occur if there are particles

If plastic is used for example, conduction is reduced as plastic is a poor conductor.