The Electromagnetic Spectrum
5 marks · NormalA communication satellite receives signals using microwaves and sends back information using infrared waves.
State the order of infrared and microwaves in the electromagnetic spectrum in terms of wavelength, starting with the longest.
Explain why microwaves are suitable for transmitting signals to and from the satellite compared to visible light.
Give one possible health effect of excessive exposure to microwaves and state a precaution to reduce the risk.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) microwaves (longest) then infrared (shorter)
(b) Microwaves can pass easily through Earth's atmosphere, while visible light is mostly absorbed or scattered; therefore, microwaves are better for long-distance communication to satellites.
(c) Potential heating of body tissue or burns; use shielding (metal screens) or limit exposure time.
Common mistakes: reversing order of waves; describing visible light instead of microwaves
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Marking points
A1 (a) · 1 mark · Correct order given: microwaves have longer wavelength than infrared.
B1 (b) · 1 mark · Microwaves can travel through Earth's atmosphere.
B2 (b) · 1 mark · Visible light is absorbed/scattered, so not suitable.
C1 (c) · 1 mark · States plausible harmful effect (heating tissue/health risk).
C2 (c) · 1 mark · States plausible precaution (shielding/metal screen/limiting exposure).
Worked solution
(a) The order, longest wavelength to shortest: microwaves, then infrared.
(b) Microwaves are suitable as they can travel easily through the Earth's atmosphere, so the signals can reach the satellite. Visible light is mostly absorbed or scattered by the atmosphere and does not pass through as easily, so it is not suitable for satellite communication.
(c) Excessive exposure to microwaves can heat or damage body tissue. One precaution is to use a metal screen in microwave ovens to reflect microwaves and keep them inside, or to limit exposure time.