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GCSE Questions - Electromagnetic Spectrum

Q2.

(a) The diagram represents part of the electromagnetic spectrum.

(i) Visible light travels through air at 300 000 000 m/s. Why can we assume that radio waves travel through air at the same speed as light? (1 mark)

All electromagnetic waves travel at the same speed through a vacuum, this is virtually the same speed in air so we can assume same speed in air.

You would not get the mark for saying 'all waves'.... only electromagnetic waves.

(ii) A radio station broadcasts at a frequency of 200 kHz. Calculate the wavelength of the waves broadcast by this radio station. Show clearly how you work out your answer. (3 marks)

Wavespeed = frequency x wavelength

c = fλ

300 000 000 = 200 000 x λ

λ = 300 000 000/200 000 = 1500 m

(iii) Draw a vertical line on the diagram above to show the position of this radio wave in the electromagnetic spectrum. (1 mark)

The graph is a log10 graph. Ordinary graphs have the x-axis increasing in regular amounts. Log10 graphs have the increase in a factor of 10.

A mark was given for a line drawn anywhere between 1000 and next section 10 000 (see graph)- the examiner accepted the answer for (a)(ii) drawn in the correct position if you got that part wrong.

(b) Many radio stations now broadcast digital signals instead of analogue signals.

(i) What is an analogue signal? (1 mark)

An analogue signal is a signal that varies continually. Its amplitude and/or frequency can change.

No mark was given for saying it is a signal loses quality when amplified.

(ii) Give one reason why a radio station would broadcast digital signals instead of analogue signals. (1 mark)

Any one from:

better quality signal

less interference/distortion/noise to signal (no mark for no interference!)

can be processed by computer/ipod

(received) signal can be restored

(c) A student thinks that because energy cannot be destroyed it is not possible to waste energy. So he leaves his radio, TV and computer on all the time, even when there is no one in the house. Explain why he is wrong about not being able to waste energy. (2 marks)

any two from:

The electrical energy required to operate the TV and radio is transformed to sound (and other energy forms). Energy not usefully transformed is wasted, so. if the sound is not listened to, it is wasted.The wasted energy is transferred to surroundings, it spreads out and cannot be made use off again in any way.

(Total 9 marks)