GCSE Physics OCR Gateway - P7

Name all the energy stores

Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear

How can energy be transferred?

Mechanically, electrically, heating, radiation

What is work done?

the process of transferring energy from one energy store to another

RECALL
Work done equation

Work done (J) = force (N) x distance (m)

What is Gravitational potential energy?

the amount of energy stored in an object due to its height above the ground

RECALL
GPE equations

GPE (J) = mass (kg) x gravity (always 10 N/kg) x height (m)
AND
GPE = weight (N) x height (m)

RECALL!
What is the equation for force with springs?

force (N) = spring constant (N/m) x extension (m)

What is elastic potential energy?

energy stored in an elastic object when work is done on it to change its shape

Equation for EPE

0.5 x spring constant (k) (N/m) x [extension]^2 (x) (m)

What is kinetic energy?

energy of motion

RECALL
kinetic energy equation

0.5 x mass (kg) x (velocity)^2 (m/s)

What is the conservation of energy?

Energy cannot be created or destroyed, only transferred

What is heat?

Total (random) KE of the particles in a substance

What is temperature?

a measure of average (random) KE in a substance

RECALL
What is specific heat capacity?

The amount of energy required to increase the temperature of 1kg of a substance by 1oC

RECALL
equation for SHC

Heat energy (J) = mass (kg) x SHC (J/kg°C) x temp. change (°C)

RECALL
What is Specific Latent Heat?

The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature

RECALL
equation for SLH

Energy (J) = SLH (J/kg) x mass (kg)

Conduction

the transfer of kinetic energy from one particle to the next. Free electrons transfer energy rapidly and make metals good conductors.

Convection

this occurs when liquids and gases are heated and expand (because their particles move further apart) The less dense fluid rises and carries the heat energy with it.

Radiation

this is when IR radiation (an electromagnetic wave) carries heat energy from one place to another. This is the only way heat energy can travel through empty space (which is a vacuum.)

Describe all the ways heat is transferred when boiling a pot of water.

- IR radiation is emitted from the fire
- Energy is transferred to the particles on the bottom of the pot and to the water by conduction
- The water particles gain more kinetic energy and become less dense
- They hotter, less dense water rises to the top and colder water sink which starts a convection current
- Energy is transferred through conduction in the pot itself
- the particles gain more KE and collide with neighbouring particles which transfers thermal energy to the end of the handle

What is power?

the rate of doing work or transferring energy

Equation for power

Power = work done (energy transferred) / time

Equation for power (IVR)

Power (w) = Current (A) (I) x Voltage (v)
OR
Power (w) = [Current]^2 (A) (I) x Resistance (Ω) (R)
OR
Power (w) = [Voltage]^2 (V) / Resistance (Ω) (R)

Equation for electrical energy

Energy (kWh) = Power (kW) x time (h)

Equation of total cost

Total Cost = Units of Energy used x Price per unit of energy

Sankey diagrams

A flow diagram that represents the total energy, the wasted energy and the useful energy of an appliance.

Reduce Heat Transfer in a House

Double Glazing
- Reduces the amount of heat energy that is transferred through windows
* Air is a poor conductor (or a good insulator) so thermal energy through conduction is decreased
* The gap between the window panes is narrow so it is harder for a convection current to start
* Heat will still be transferred via radiation though
Cavity Walls
- Heat is conducted through the solid inner wall to air in the cavity wall
- Heated air will rise carrying heat energy with it (convection)
- Walls can be filled with cavity wall insulation containing many small pockets of trapped air

Equation for efficiency

Efficiency = useful energy output / total energy input x 100