Infrared
4 marks · NormalA remote control uses infrared radiation to operate a television.
State why infrared is suitable for this use rather than visible light.
Suggest why remote controls do not work well when something is placed in front of the TV's infrared sensor.
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(a) — · must show Not harmful to eyes/skin at low power, Not visible, avoids distraction, Works only over short distances, so less interference
(b) — · must show Infrared waves have low penetrating power, Blocked by objects, cannot reach sensor
Common mistakes: Saying visible goes through objects
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Marking points
B1 (a) · 1 mark · States infrared is not harmful/discreet/not visible.
B2 (a) · 1 mark · States infrared's low range prevents interference/operates over short distances only.
B3 (b) · 1 mark · States that something placed in front blocks or absorbs the infrared signal.
B4 (b) · 1 mark · Explains that the sensor cannot detect the signal if blocked/infrared has low penetration power.
Worked solution
a) Infrared is not harmful to humans at the power used and is not visible, so it does not distract from viewing. It also has a short range, reducing interference with other devices.
b) Infrared has low penetrating power and cannot pass through objects. If something is placed in front of the sensor, the signal cannot reach it and the TV does not respond.