# Waves, fields and nuclear energy

AQA unit 4

## Waves

A wave transfers energy through oscillations without transfer of material.

Time period: Time for one oscillation.

Frequency: The number of oscillations per second.

Amplitude: Maximum displacement.

Wavelength: The distance between two neighbouring points in phase.

Wave equation: c=fxlambda

Transverse: Where direction of oscilation is at right angles to the direction of energy transfer.

Longitudinal: Where direction of oscillation is parallel to the direction of energy transfer.

Polarisation: Only transverse waves can be polarised. Most light sources produce unpolarised light. A polaroid sheet removes osscilations in one direction.

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## Stationary waves

These are produced when two identical progressive waves moving in opposite directions combine together. The result is a wave pattern which appears stationary at certain points amd the wave does not seem to progress.

Vibrations in a string

The dominant mode of vibration produced in a string is the fundamental.

At the end of the string are nodes. There is no vibration here at the centre is an antinode where there is maximum vibration.

Vibrations in pipes

When a tube is made to resonate, an antinode is produced at the top. Remember that a sound wave is a longitudinal wave so the air particles are actually oscillating vertically.

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## Single slit diffraction

When a wave passes through a gap in a barrier which is not equal in size to the wavelength, a diffraction pattern results. sin feta= lambda/width of gap This effect produces a central bright fringe, which is broad. to either side are much smaller less bright fringes which are not equally spaced.

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## SHM

An object is in SHM if it's acceleration is proportional to displacement, from a fixed point and is directed towards that point. Energy- The law of conservation of energy applies, at any point in the motion the P.E added to the K.E gives the total energy.

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## Properties of waves

Superposition of waves When two or more waves meet at a point, resultant displacement is equal to the sum of the two displacements. Constructive interference- Two waves arrive at the same point, through superposition to create a large wave they must arrive in phase. Destructive interference- Two waves arrive at the same point superposition, smaller wave as they arrived in anti phase.

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## Oscillations

Free- a body oscillates with a constant amplitude without loosing or gaining energy, at its natural frequency. Forced- It is where the energy to make the object oscillate is from an external source oscillating moving at the driving frequency. Damped- the amplitude decreases steadily due to it loosing energy to the environment. Resonate- it vibrates with a large amplitude, its vibrating when the natural frequency is the same as the driving frequency.

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