# Physics P3

Physics P3 revision notes

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• Created by: Aamina
• Created on: 27-05-10 17:43

## Ultrasound

Ultrasound has a frequency higher than 20,000 Hz and are unable to be heard by humans

Uses: pre natal scanning and cleaning- vibrations knock dirt off

the longer the ultrasound takes to read a detector, the further away the object is.

Frequency- the number of waves that pass a point each second.

Height on an oscilloscope trace = amplitude

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## Sound- Longitudianal Waves

Sound waves cannot travel through a vaccum. This requires particles

Sound is produced by mechanical vibrations.

Sound waves can be reflected and refracted.

Humans can hear sound waves between 20Hz- 20,000Hz

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## Electromagnetism- Motor Effect

Split ring ammutator- keeps the coil rotating

Brushes- connect the slip rings to the circuit.

When a wire is placed in a magnetic field, it experiences a force.

The force is greatest when the wire is perpendicular to the magnetic field

The force is 0 when the wire is parallel to the magnetic field because the magnetic field is not cut.

The force acts on both sides of the coil. this causes the coil to turn when a current passes through.

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## Electromagnetism- Motor Effect, Uses

Loudspeaker

When a current passes through the coil it vibrates due to a force due to the motor effect.

The current change direction therefore the force changes direction back and forth causing the diaphgram to vibrate.

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## Turning Forces

Circular motion

Objects moving in a circular path e.g a rubber bung spun clockwise, a car going around a roundabout.

Its velocity changes direction producing an acceleration toward the centre. the centripetal force is due to friction.

To stay in orbit at a certain distance, objects must have a certain speed.

Factors affecting Centripetal Force:

Increasing mass Increasing speed Increasing the radius

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## Turning Forces- Gravitational Attraction

The earth, sun, moon and other orbits attract each other with a force called gravity.

Gravitational Force provides the centripetal force that allows planets and satellites to stay in circular orbits.

Factors affecting Gravity

The bigger the mass, the greater the force of gravity

The bigger the distance, the smaller the force of gravity

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