# Physics: Section C, Waves

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• Created by: marita
• Created on: 26-12-13 23:09

## Types of Waves

Waves: They transfer energy without transfering matter. They don't need to travel through a medium

Transverse Waves: They vibrate across the direction to which they are moving.

Examples; light, microwaves, x-rays

Longitutinal: Waves: They vibrate along the direction to which they are moving

Examples; sound waves

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## Definitions & Equations

Period (T) : One complete cycle of one wave; units 'second' ,'s'

Freequency (f) : Number of cycles of a wave that occur in 1 second; units 'Hertz', Hz'

freequency=number of waves

time taken

T= 1               F= 1

F                    T

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## Wave Speed

Wave Speed :

v=λf

v= wave speed (m/s)

λ= wavelength (m)

f= freequency (Hz)

*wavelentgh= distance between 1 wave

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## Electromagnetic Spectrum Characteristics

• Transverse
• Travel in a vacuum
• Travel very fast: 3x 10^8 m/s
• Vibrations are electric and magnetic fileds

*the very first ones have low freequencies and large wavelengths

*the very last ones have high freequencies and small wavelegths

radio waves,   micro waves,  infra-red,  light,  ultra violet,  X-ray,  gamma

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## Uses of Waves

Radio waves:                                                           X- rays:

•     long, medium, short-wave radio/TV (UHF)            *X-radiography observes internal                                                                                      structure of objectse.g.human bones

Microwaves:                                                               Gamma rays:

• mobile phones, satellites, cooking                         *sterilisation of food and equipment,

• night vision, cooking, remote controls

Light:

• seing, communication (optical fibres), photographs

Ultraviolet (UV):

• UV luorescent tubes, UV tanning lamps
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## Effects of Waves

Microwaves:

• excessive use can heat internal tissues

Infra-red:

• skinburns

Ultraviolet:

• skin cancer, blindness, sunburn, blistering

X-rays:

• overexpsure can cause cancer

Gamma rays:

• gene mutation >cancer   *highly penetrating
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## Digital & Analogue Signals

Analogue Signals:  informatiom > electrical voltages/currents that vary > amplified wave

+ fine definition

- when amplified acompanying noise is amplified as well

- it takes a wider range of freequencies to broadcast an analogue signal

Digital Signals: information > binary code ( 0 & 1) > series of electrical pulses

+ regeneration creates a clean accurate copy of the original signal

+ easier to design and build

+ data that are easier to process

+ more programmes can be broadcast over the same freequencies

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## Light Waves-Reflection

angle of incidence (i) = angle of reflection

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## Images in plain mirror

rays from objects in the room > reflected to the mirrror > reflected in your eyes > virtual images

Properties:                                          *virtual image: rays of light don't actually pass through

• Image is as far as is the object behind   *real image: rays of light pass through them
• Image has the same size as he object
• Image is laterally inverted
• Image is virtual

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