# Working Waves

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• Created by: nat kay
• Created on: 12-04-16 12:07
Define amplitude
The maximum displacement
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Define wavelength
The distance between two similar points on the wave
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Define period
The time between two similar
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Define frequency
The number of cycles of a wave passing a point in unit time
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What is phase?
Phase is the difference between two separate waves. It can be expressed as a distance, time difference, fraction of a cycle, an angle in degrees or angle in radians
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What is the word equation?
velocity = distance/time
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Define a transverse wave.
Where the displacement is at right angles to the wave direction
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Define a longitudinal wave.
Where the displacement is parallel to the wave direction.
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Define a polarised wave.
Where the displacement is only one of the possible transverse directions.
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What type of wave is a electromagnetic wave?
Transverse wave
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Name features of electromagnetic waves.
They can travel across a vacuum, the speed at which they travel at is 3x10(8) ms(-1)
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Name the 7 regions of the electromagnetic spectrum.
Gamma, x-ray, ultraviolet, visible light, infrared, microwaves and radiowaves
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What is spatial resolution?
How well we can distinguish between objects at slightly different places
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What is thermal resolution?
How well we can distinguish between objects at similar temperatures
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Define refraction.
It is the effect that causes a change of direction of light when it goes from one medium to another in which it travels at a different speed
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Define angle of incidence.
It is the angle between the incident ray and the normal
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Define angle of refraction.
It is the angle between the refracted and the normal
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What is total internal reflection?
It occurs when the angle of incidence is greater than the critical angle, which makes the ray no longer emerge from the block
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What conditions do optical fibres need in order to work?
The material outside the fibre has a lower refractive index than the glass, and the angle of incidence must be greater than the critical angle
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Name 4 advantages of using optical fibres.
They have a very large capacity , they have low material costs, small cable size and makes wiretapping more difficult
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Name a disadvantage of optical fibre.
They are expensive to produce and install
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What are digital signals?
They have only certain discrete value (binary)
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What are analogue signals?
They are continuously variable - they can have any value in a range
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What is amplitude modulation?
The amplitude of the radio carrier wave is varied according to the sound signal. The frequency of the modulation will be the same as the frequency of the sound
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What is frequency modulation?
The frequency of the radio carrier wave is varied according to the sound signal. the amplitude of the wave is constant
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The term used when signals are sent from a base station to a mobile phone
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The term used when signals are sent from a mobile phone to a base station
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Define full duplex.
The term used when signals are sent and received on different frequencies so that you can send and receive at the same time
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Define half duplex.
The term used when signals are sent and received on the same frequency so that you have to take it in turns to talk and listen
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What is Frequency Division Multiple Access (FDMA)?
Available frequencies are shared between users
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What is Time Division Multiple Access (TDMA)?
It allows several users to share the same frequency by dividing the signal into different time slots
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What is Code Division Multiple Access (CDMA)?
Calls use frequencies over the whole band. Each call has a unique code to identify it
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What is Pulse Code Modulation (PCM)?
A form of analogue to digital conversion. The signal is sampled at equal intervals within each cycle. The size of this voltage is converted electronically to a number. This number is expressed in binary form and the reconverted to form a smooth curve
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What is one way in which blurred images can be reduced?
A wide beam. The width of the beam can be limited by lead placed just outside the x-ray machine and before the beam reaches the patient. Lead absorbs x-rays
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How does filtration on an x-ray work?
Filters are used to remove x-rays with lower frequencies, as these are either absorbed by the skin an unnecessary dose or scattered blurring the image, increasing the proportion of useful higher frequency waves
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What is another way of not getting a blurred x-ray image?
By using a grid. This is placed between the patient and the film/detector. The grid is made of strips of lead with gaps that allow direct radiation to pass but block scattered radiation
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What is an image-intensifying screen?
It uses layers of fluorescent material to convert the remaining x-ray energy which isn't absorbed into light and by using this light it increases the exposure of the film
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## Other cards in this set

### Card 2

#### Front

Define wavelength

#### Back

The distance between two similar points on the wave

Define period

Define frequency

What is phase?