Thermal physics

Question 1

What is thermal energy?

Answer 1

The energy a substance has because of the motions of its particles

Question 2

What is conduction?

Answer 2

• The transfer of heat from one place to another through the passing on of kinetic energy between the particles of a substance
• This happens mainly within solids (to a small degree in liquids/gases), where the particles are in close proximity without moving
• Conduction can also transfer heat from a substance in one state to a substance in another state, if the two are in contact

Question 3

Can heat be transferred via conduction in a vacuum? Why?

Answer 3

No; A vacuum does not contain particles

Question 4

What is meant by a “thermal conductor”?

Give an example

Answer 4

A ‘good thermal conductor’ means a fast conductor, through which heat transfers by conduction relatively quickly
Examples:
-Metals(Cu/Au/Ag)

Question 5

What is meant by a “thermal insulator”

Give examples

Answer 5

An ‘Insulator’ means a slow conductor, through which heat transfers by conduction relatively slowly
Example:
-Plastics
-Wood
-Gases (air)
-Foam*
-Fibreglass*
*materials that contain a lot of trapped air

Question 6

Why do solids typically make better conductors than liquids and gases?

Answer 6

• Gases are typically poorer conductors than liquids and solids; the particles in a gas are far apart relative to their size
• Collisions are not frequent enough to transfer kinetic energy between particles as quickly as in liquids and solids
• Liquids are typically poorer conductors than solids
• In a liquid the particles aren’t held tightly together
• it takes longer for kinetic energy to be transferred between particles

Question 7

Why do metals make the best conductors?

Answer 7

• When part of a metal becomes hotter, not only the ions but also the free electrons gain kinetic energy
• free electrons can transfer energy much faster, by moving through the lattice and colliding with ions and with each other

Question 8

What factors affect the rate of conduction?

Answer 8

• temperature difference between the two objects; the higher the temp diff, the higher the rate
• distance between the two objects; the shorter the distance, the higher the rate
• Surface area in contact with connecting material; the; larger the area, the higher the rate

Question 9

How does temperature affect the density of a fluid?

Answer 9

• When the temperature of a fluid increases, the speed of its particles increases
• The particles collide with each other more frequently and with greater force
• Its particles move further apart, on average
• The fluid expands
• The density of the fluid decreases, because there are now fewer particles (and hence less mass) per unit volume

Question 10

What is convection?

Answer 10

occurs when higher energy particles move to cooler regions, heating them up, and the heat is transferred by “convection currents”

Question 11

Describe what is meant by “convection currents”, with the example of a radiator

Answer 11

1. Air particles gain energy, move around more energetically, causing that pocket of air to expand. It becomes less dense, and so it rises.
2. It moves up and away from the radiator (the heat source)
3. As it does so, it cools, becoming denser and sinking.
4. This creates a cycle of air flow in the room, known as a convection current, which allows all the air particles in the room a chance to be near the radiator at some point, to heat up

Question 12

What is thermal radiation or Infrared radiation?

Answer 12

a type of electromagnetic wave that is one of the parts of the electromagnetic spectrum;
-it travels at the speed of light and does not need a medium in which to travel

Question 13

What type of objects emit/ absorb radiation?

Answer 13

ALL OBJECTS EMIT AND ABSORB RADIATION

Question 14

How does temperature affect the rate of radiation emission/ absorption?

Answer 14

[TEMPERATURE]:

• The higher the temp of an object, the higher the rate at which it emits thermal radiation
• If an object is at a lower temperature than its surroundings, then it absorbs thermal radiation at a higher rate than it emits it
• If the object is the same temperature as it’s surroundings, it’ll emit and absorb equal amounts of radiation

Question 15

How does colour affect the rate of radiation emission/ absorption?

Answer 15

• Matt, dark surfaces are very good at both absorbing and emitting heat radiation;increase the rate
• shiny, white surfaces will tend to reflect heat radiation; have a low rate of absorption/emission

Question 16

How does surface area affect the rate of radiation emission/ absorption?

Answer 16

-The greater an object’s surface area, the higher the rate of absorption and emission

Question 17

What are the 3 ways an object can react to thermal radiation hitting it?

Answer 17

The thermal radiation will be

• Absorbed
• Transmitted (passes through the object)
• Reflected

Question 18

If there is a transfer of thermal energy to/ from an object, and it is not changing state, what affects it’s change in temperature?

Answer 18

• The mass of the object

- The type of material it is made of

Question 19

What is meant by the term “specific heat capacity”? What equation can be used to express this?

Answer 19

The amount of energy required to raise the temperature of 1 Kg of a substance by 1 degree Celsius

SHC= [thermal energy]/[(mass) x (temp change)]

SHC: J Kg-1 C-1
Energy: J
Mass: Kg
Temp: degrees Celsius