Energy Stores & Transfers

What are all the energy stores?

Kinetic, gravitational, elastic, magnetic, electrostatic, chemical, nuclear, thermal,

What are all the energy transfer pathways?

mechanical, Electrical, Heating, radiation

What energy transfer pathway is light?

radiation

Why are no energy transfers 100% effecient?

Eneryg is dissipated to the thermal store of the surroundings

How do you work out energy efficiency

useful energy output / total energy output

Why is metal a good thermal conductor?

It is a solid with free electrons

What are bad thermal conductors called?

Insulators

How does Thermal conduction work?

atoms vibrate and bump into eachother, transferring energy

How does convection work?

When fluid particles are heated, they gain kinetic energy.
When they gain kinetic energy, they spread apart and the fluid becomes less dense
The less dense fluid rises and is replaced by denser, cooler fluid.
The old hot fluid cools down and becomes denser and sinks back down.

Order of colours for thermal radiation, best absorber / emitter to worst

Black, dark, white, shiny

Practical for investigating conduction

Attach ball bearings to strips of metal using wax.
Hold the 4 metals at equal points around a conduction ring

Heat middle of conduction ring and measure time taken for wax to melt and ball to drop.
Ball that drops the fastest is the best conductor.

Practical for investing convection

Use potassium permanganate crystals in a beaker of water.
Heat the water, and the hot water will rise then drop when cool.
The dissolved crystals will clearly demonstrate the convection.
Repeat at different temperatures and compare.

Practical for investing radiation

fill 4 flasks of different colours with same temp hot water
Measure every 30 secs temp
different colour flasks will have different temps due to radiation rates

How do you reduce wasteful energy in the form of conduction?

Use insulating material

How do you reduce wasteful energy in the form of convection

prevent the fluid from moving

what is 1 example of a way to insulate

Use fiberglass

How does insulation work?

insulator contains trapped air, prevents convection
trapped air is also a poor thermal conductor. This reduces rate of energy transfer, keeping object warm.