Transcript P1 5.5 Questions and answers File

P1 5.5 – Questions and answers
1 A radio station broadcasts on 2 million Hz, a TV station
broadcasts on 2000 million Hz, and the emergency services use
a radio frequency of 200 million Hz. Which uses the longest
wavelength?
A The radio station
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P1 5.5 – Questions and answers
2 Why do microwave ovens have a safety lock to prevent
them operating while the door is open?
A The microwaves would heat up people who were close to
the oven, and cook them.
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P1 5.5 – Questions and answers
3 A radio aerial receives a radio broadcast. Describe two
things that happen to the metal aerial.
A There is an alternating current (or voltage) and the metal
gets hotter.
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P1 5.5 – Questions and answers
4 BBC 4 long-wave radio broadcasts at 198 kHz. What is the
wavelength?
A 1515 m
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P1 5.5 – Questions and answers
5
BBC Radio 1 is broadcast with a wavelength of 3.01 m.
What frequency is this?
A
100 million Hz
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P1 5.5 – Questions and answers
6 Describe the different ways that a television signal might
reach your TV set.
A It might be added to radio waves that are broadcast from a
transmitter and be reflected from the ionosphere and
diffracted through valleys before reaching the aerial; it
might be added to microwaves and sent up to a satellite
that receives it and transmits it down to a satellite dish.
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P1 5.5 – Questions and answers
7 Explain why radio waves can be received over a large area
but microwaves need repeating transmitters on hills and
buildings.
A Radio waves are reflected from the ionosphere and
diffracted by hills and valleys, but microwaves are not.
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P1 5.5 – Questions and answers
8 A student says that we should not use microwaves for
communications because microwaves cook meat and so
they will cook us. Explain to the student what is wrong with
this conclusion.
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P1 5.5 – Questions and answers
A The microwaves used for communications are much lower
power than those in ovens. The microwave oven uses a
particular wavelength/frequency that is strongly absorbed by
water and the oven is designed to reflect the microwaves
until the food absorbs them all. There are other microwave
wavelengths/frequencies that can be used for
communications that do not have the strong heating effect.
The transmitters can be placed high up where people are
not close to them and can be switched off if any workers
have to go near them. Microwaves have been used for
communications for many years and we do not have cases
of people being cooked. The signal from the transmitter is
spread out, so the signal at the receiver is much lower.
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