# physics p1b

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• Created by: ayesha
• Created on: 12-08-11 16:15

## Electromagnetic spectrum

• Electromagnetic waves are electrical and magnetic disturbances that transfer energy from one place to another.
• There are 6 electromagnetic waves that go from low frequency to high frequency and the lower the frequency of the wave the bigger the wavelength and vive versa.
• The electromagnetic waves in order from low frequency to high frequency are: radio -> microwave -> infa-red -> light -> ultraviolet radiation -> X-rays and gamma rays
• Describing waves: A wave can transfer energy without transferring matter. The energy they transfer depends on wavelength of the waves. This is why waves of different wavelengths have different effects.
• The amplitude of the wave is the height of a wave from the middle to the top of the wave.
• The lamba of the wave is the wavelength of the wave, the distance from a pint on 1 wave to the same point on the net wave.
• The frequency of the wave  is the number of complete waves passing a point each second / it is 1 second divided by the time of the wave
• the time of the wave is the time for 1 wave to pass a point / 1 second divided by the frequency of the wave
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## Electromagnetic spectrum continued

• Example of question on waves: A surfer sees 10 waves go past him in 5 seconds, and the wavelength of the waves are 3m. What is the speed of the wave.
• speed = distance/ time
• The distance of the wave is 3m , the time of 1 wave is 5 seconds divided by 10 ( which is equal to 0.5 seconds) therefore the speed of the wave is 3m/0.5s = 6m/s
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## Speed of electromagnetic waves

• All electromagnetic waves travel at speed of 300 millions m/s through space or in a vacuum = distance wave travel each second
• wave speed (m/s) = frequency (Hz) X wavelength (m)
• Example: A mobile phone gives out electromagnetic waves of frequency 900 illion Hz. Calculate the wavelength. Speed of elctromagnetic wave = 300 million m/s
• Solution: wavelength = wave speed/frequency                                                                =300 000 000/ 900 000 000 = 1/3m =0.33m
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• Radio: A metal aerial will have an electric current created in it that changes at the same frequency as the radio wave is absorbed.
• Speed: 300 million m/s
• Frequency: 300 000 Hz to 300 million Hz
• Wavelength: 100km to 1 mm
• What transmits radio waves: music pictures, broadcasting, mobiles, Blue-tooth, wi-fi, sky TV, clocks
• Radio waves side effects: possible risk of cancer
• Reducing exposure of radio waves:  moving away from the transmitter
• Radio waves used as: television signals, GPS, wi-fi
• Radio waves are emitted from an aerial when we apply an alternating voltage to the aerial. The frequency of radio waves produced are same as frequency of alternating voltage.
• When radio waves pass across a receiver aerial, they cause a tiny alternating voltage in the aerial. The frequency of the alternating voltage is the same as the frequency of radio waves received.
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