Physics paper 1

Energy :

Energy is never created or destroyed

Only transferred between different forms/objects

Gravitational potential energy -> Energy an object holds because of its position in a gravitational field

Elastic potential energy -> energy held in an already stretched spring

Chemical energy -> held in chemical bonds

Nuclear energy -> from breaking atoms apart

Energy stores can be transferred :

Mechanically - through stretching an elastic band

Electrically - plugging something into a socket

Heating and by radiation - light or sound waves

Group of objects - System

Open system - energy can be transferred to the outside of the system

Closed system - energy cannot be transferred to the outside system and stays inside the system

For a closed system overall exchange is always 0

Work done -

Can be mechanical : force moves an object

Electrical : energy required to overcome the resistance inside a wire

Specific heat capacity :

Specific heat capacity means the total energy stored within a substance or system

Temperature is the measure of the average internal energy

Specific heat capacity of liquids - The total energy required to increase the temperature of a substance by 1 degree or amount of energy released as a substance cools

Change in internal energy (In Joules) = Mass (In kg) x Specific heat capacity (J/kg) x Change in temperature

Conduction, convection and radiation

Conduction - Heat energy is transferred through collisions onto neighbouring vibrating particles (Solids)

Thermal conductivity - how well a material conducts heat

Insulator - doesn't conduct heat very well (Stops heat from escaping)

Convection - energy transferred by particles moving position, rather than vibrating (Liquids)

When liquid is heated, particles gain kinetic energy and start to move faster. They then spread apart and become less dense. Then the less dense fluid rises up. The fluid then cools down becoming dense and sinks back down. This is a cycle and is called a convection current

Radiation - heat energy is transferred without particles, but with infrared waves (Can travel through a vacuum)

All objects emit and absorb this radiation.

Power and Work done

Power = rate at which energy is transferred (1st definition)

Power (watts) = Energy transferred (Joules) /time (seconds)

Power = rate at which work is done (2nd definition)

Power (watts) = work done (Joules) /time (seconds)

Work done - Measure of energy transferred, when a force is used to move an object at a certain distance

Hydroelectricity and Tidal Barrages

Hydroelectric and tidal barrages - both have higher sea level on one side and have a big dam which prevents water from flowing through. We use the difference of water levels to generate electricity (the stored water has a huge amount of GPE), The fall of water through turbines spins them and helps the generation of electricity

Hydroelectric dams trap water upstream in a reservoir.

Tidal barrages trap water as the tide comes in, which causes a higher sea level on one side.

Pros :

0 pollution
Reliable
Low running costs

Cons :

Big impact on surrounding environment
Setup is expensive
Stops boat and fish travel