Radiation travels in straight lines: True
Radiation can travel through a vacuum: True
Radiation requires particles to travel: False
Radiation travels at the speed of light: True

1. Which of the following is not a method of heat transfer?
Insulator

2. In which of the following are the particles closest together?
Solid

3. How does heat energy reach the Earth from the Sun?
Radiation

4. Which is the best surface for reflecting heat radiation?
Shiny white

5. Which is the best surface for absorbing heat radiation?
Dull black

Conduction, convection and radiation

Energy flow [Thermal transfer]
high temperature -> low temperature

- Conduction
- Thermal conductors - materials that allow thermal energy to transfer through them quickly
- Thermal insulators don't
- One end of the conductor is heated
- Atoms that make up its structure vibrate vigorously
- Atoms linked together - increased vibration passed on to other atoms
- Kinetic energy passes through the whole material

- Metals are good conductors
- Contain freely moving electrons
- Transfers energy rapidly
- Electrons travel all over the metal - take thermal energy with it
- Vacuum is perfect insulator

- Convection
- Occurs in liquids and gases
- Material flows ('fluids')
- Heated
- Energy transferred to particles
- Move faster and further apart
- Heated fluid less dense than unheated fluid
- Less dense fluid rises above the more dense (colder) fluid
- Fluid circulates
- [Convection current] - How thermal energy is transferred
- Insulators (ceiling tiles etc.) contain trapped air pockets to prevent air from circulating and transferring thermal energy by convection

- Radiation
- Does not need particles
- Can travel through vacuum
- Radiated heat energy carried mainly by infrared radiation
- Hot objects radiate more infrared than cold objects

- Dull black surface - Good emitter and good absorber
- Bright shiny surface - Poor emitter and poor absorber

- Leslie's cube - Different surfaces (shiny, dull, etc) to show how they emit and absorb thermal radiation at different rates

1. What is the most common heat transfer mechanism in solids?
Conduction - the particles are close together

2. What is the most common heat transfer mechanism in liquids and gases?
Convection - the particles are fluid

3. What is the only heat transfer mechanism in a vacuum?
Radiation - both conduction and convection require particles

4. Why can't conduction happen in a vacuum?
Conduction requires particles

5. What happens to the space between the molecules in a gas when you heat it?
The space between the molecules increases when you heat it

6. What happens to the density of a gas when you heat it?
The density of a gas increases when you heat it

7. Why can't convection happen in a solid?
Because the particles in a solid aren't fluid

1. Chemical potential energy -> Electrical energy -> Kinetic + heat + sound energy

2. Elastic potential energy -> Kinetic + heat + sound energy

3. Chemical potential energy -> Electrical energy -> Light + heat energy

4. Chemical energy -> Kinetic + heat + sound energy

4.2

describe energy transfers involving the following forms of energy:
thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Extension: What does "potential" mean?
Stored energy

exam correction list/"to remember"

3.13

Recall the detrimental effects of excessive exposure of the human body to electromagnetic waves, including:

Microwaves: internal heating of body tissue
Infrared: skin burns
Ultraviolet: damage to surface cells and blindness
Gamma rays: cancer, mutilation