# Physics(2)

## Distributing electricity

In the UK, the National Grid distributes electricity from power stations to consumers.

The National Grid

Mains electricity is distributed to homes, shops, offices and factories by cables from power stations, which may be hundreds of kilometers away.

When electrical energy travels along a wir, some of it is dissipated. Increasing the voltage to 400kV reduces current, which reduces the amount of energy wasted.

High voltage is very dangerous. The electric shock caused by touching a high-voltage cable can kill.

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## Properties of waves

WAVES transfer ENERGY from one place to another. Waves are carried by something that is oscillating.

Transverse

Mechanical waves must move through solids, liquids or gases. They cannot travel through a vacuum. They may be tranverse or longitudinal.

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## Waves

REFLECTION happens when a wave bounces off the interface between two materials. The wave changes direction but doesn't cross the interface.

REFRACTION happens when a wave crosses an interface between two materials. The wave changes direction unless the rays hit the interface at right angles.

DIFFRACTION happens when waves pass through a gap or over an obstacle that is similar in size to the wavelength of the wave. The wave spreads out through the gap.

A ray is a line showing the direction the waves are travelling.

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## Relfection in mirrors

When waves are reflected, the angle of incidence is equal to the angle of reflection.

The INCIDENT RAY shows the direction of waves moving towards a surface.

The NORMAL is an imaginary line drawn perpendicular to the surface where the incident ray meets it.

The REFLECTED RAY shows the direction after reflection.

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## Sound

Sound waves are longitudinal waves that cause vibrations in materials.

The material that sound waves travel through is known as the MEDIUM. Sound waves can travel through solids, liquids and gases. The PITCH of a sound is determined by its frequency. A high-pitched sound is a wave with a high frequency. The LOUDNESS of a sound is related to the amplitude of the vibrations.

It is easier to show sound waves as if they are displayed on an oscilloscope. The higher the peak, the more the particles are compressed.

Echoes

Sound waves can be reflected off surfaces. We hear the reflections as ECHOES. Echoes arrive after the main sound because the waves have travelled further.

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## Red-shift

The Doppler effect can be used to measure the speed and direction of moving objects.

The Doppler effect

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