# Telecommunications

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1. In air, the speed of sound is....?
340 m/s
2. In air, the speed of light is...?
3 x 108 m/s
3. What is the formula for speed-distance-time?
d=vt
4. What is the wave equation?
v=f λ
5. What is another equation you can use to work out the frequency of a wave?
f = n ÷ t
6. What is the amplitude of a wave?
The distance from the zero line to the crest or the trough
7. What is the wavelength of a wave?
The distance from any point on a wave to the point where it starts to repeat.
8. What is the speed of light in optical fibres?
2 x 108 m/s
9. 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
10. 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
11. 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.
12. 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.
13. 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.
14. To increase the brightness of a television picture _____ electrons are fired at the screen every second?
more
15. To decrease the brightness of a television screen _____ electrons are fired at the screen every second?
less
16. Name the parts of a television
• Ariel
• Tuner
• Audio and visual decoder
• Audio and visual amplifier
• Power supply
• Speaker
• Television tube
17. What are the three main colours on a TV screen?
• Red
• Blue
• Green
18. How do you make yellow?
Red and Green light
19. How do you make magenta?
Blue and Red light
20. How do you make cyan?
Green and Blue light
21. How do you make black / white light?
• Black - light up no dots
• White - Blue, Red and Green light
22. 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.
23. 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.
24. What is diffraction?
The bending of a wave around an obstacle
25. Long waves diffract ______ than short waves?
more
26. 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
 Author: Anonymous ID: 62751 Card Set: Telecommunications Updated: 2011-01-29 17:11:26 Tags: Physics Telecommunications Folders: Description: Standard Grade Physics - Telecommunications Show Answers: