# Physics GCSE (1)

Science A GCSE - Physics

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Infrared radiation is energy transfer by electromagnetic waves.

The hotter an object is, the more infrared radiation it emits in a given time.

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Dark, matt surfaces emit more infrared radiation than light, shiny surfaces.

Dark, matt surfaces absorb more infrared radiation than light, shiny surfaces.

Light, shiny surfaces reflect more infrared radiation than dark, matt surfaces.

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## STATES OF MATTER

The particles in a solid are held next to each other in fixed positions.

The particles in a liquid move about at random and are in contact with each other.

The particles in a gas move about randomly and are much further apart than particles in a solid or liquid.

EFFICIENCY = USEFUL ENERGY                                                  TOTAL ENERGY         X100

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## CONVECTION

CONVECTION IS THE TRANSFER OF ENERGY IN A MOVING LIQUID OR GAS.

Convection currents are caused because fluids (liquid or gas) rise when they're hot. When they cool down they fall. Convection currents transfer energy from the hotter parts to the cooler parts.

Density decreases in a fluid when heated and causes circulation (convection current) and density increases in a fluid when cooled down.

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## EVAPORATION AND CONDENSATION

EVAPORATION IS WHEN A LIQUID TURNS INTO A GAS.

CONDENSATION IS WHEN A GAS TURNS INTO A LIQUID.

A liquid evaporates and cools when its faster-moving molecules escape into the surrounding air.

When water condenses on glass, water molecules in the air form a liquid on the glass.

U-values

A U-value tells us how much energy per second passes through different material.

The lower the U-value, the more effective the material is as an insulator.

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## SPECIFIC HEAT CAPACITY

The specific heat capacity of a substance is the energy needed or heat transferred to 1kg of the substance to raise its temperature by 1'c.

Specific heat capacity = energy required to heat up

mass x temperature change

Energy  = mass x specific heat capacity x temperature change

Things that heat up quickly have a lower specific heat capacity. Things that heat up slower have a higher specific heat capacity.

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## FORMS OF ENERGY

Chemical energy: energy stored in fuel (including food), released when chemical reaction takes place.

Kinetic energy: the energy of a moving object.

Gravitational potential energy: the energy of an object due to its position.

Elastic potential energy: the energy stored in a springy object when you stretch or squash it.

Electrical energy: energy transferred by an electric current.

A torch's energy transfers...

chemical energy (battery) --> electrical energy --> light energy + energy heating                                                                                                        surroundings

Conservation of energy...

ENERGY CANNOT BE CREATED OR DESTROYED.

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