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In air, the speed of sound is....?
340 m/s
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In air, the speed of light is...?
3 x 108 m/s
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What is the formula for speed-distance-time?
d=vt
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What is the wave equation?
v=f λ
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What is another equation you can use to work out the frequency of a wave?
f = n ÷ t
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What is the amplitude of a wave?
The distance from the zero line to the crest or the trough
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What is the wavelength of a wave?
The distance from any point on a wave to the point where it starts to repeat.
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What is the speed of light in optical fibres?
2 x 108 m/s
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Name and describe the parts of a radio
- Ariel - picks up many signals
- Tuner - selects one frequency
- Decoder - gets the audio signal back from the modulated wave
- Power supply - supplies energy to the amplifier
- Amplifier - makes the audio signal stronger
- Speaker - changes electrical signal into sound
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What is amplitude modulation?
At a radio station, a low frequency audio wave is combined with a very high frequency radio wave called a carrier wave. The amplitude of the radio changes (modulates) a process called amplitude modulation
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Explain "Line Build Up"
- The inside of a television screen is coated with a large number of phosphor dots, arranged in many lines.
- When electrons hit the phosphor dots, the dots give out light for a fraction of a second.
- An electron beam is moved across the screen, one line at a time. This happens 25 times every second. This process is known as line build up.
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Explain "Image Retention"
- There are 25 different pictures on a TV screen every second.
- The human eye/brain system holds on to the image for a fraction of a second before replacing it with another image - this is known as image retention.
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Explain why we see a moving image on TV
As the pictures on a television screen are changing so quickly, the eye/brain system cannot detect them changing. It blends successive particles together, so we see a moving picture.
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To increase the brightness of a television picture _____ electrons are fired at the screen every second?
more
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To decrease the brightness of a television screen _____ electrons are fired at the screen every second?
less
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Name the parts of a television
- Ariel
- Tuner
- Audio and visual decoder
- Audio and visual amplifier
- Power supply
- Speaker
- Television tube
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What are the three main colours on a TV screen?
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How do you make yellow?
Red and Green light
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How do you make magenta?
Blue and Red light
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How do you make cyan?
Green and Blue light
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How do you make black / white light?
- Black - light up no dots
- White - Blue, Red and Green light
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What does fitting a curved reflector dish to a reciever ariel do to the signal and why?
It makes the signal stronger because it collects all of the signal and reflects it all to the ariel.
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What is meant by a Geostationary Satellite?
- A satellite that appears to be stationary above the earth as the earth spins.
- The period of the satellite will be 24 hours - the same period as the earth takes to rotate.
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What is diffraction?
The bending of a wave around an obstacle
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Long waves diffract ______ than short waves?
more
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What are the advantages of optical fibres over copper cables?
- There is little loss of energy due to the pure glass
- Fewer repeater units are needed
- They are free from electrical interference
- Much lighter than copper cables
- They cost less
- They carry more signals
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