The electromagnetic spectrum — GCSE Physics practice questions

Question 1

A hiking water bottle has a small battery-powered LED in its cap.
When the cap is screwed on, the LED shines invisible radiation into the water for one minute. The radiation kills bacteria in the water.

Which region of the electromagnetic spectrum does the LED emit?

Accepted Answer

D: ultraviolet. Ultraviolet damages the cells of bacteria and viruses, so it is used to sterilise water. Small LEDs can emit ultraviolet. Gamma rays also sterilise, but they come from radioactive nuclei, not from an LED, and would need heavy shielding.

Question 2

Three jobs use electromagnetic waves:

- a drone camera finds hidden hot spots under the smoke of a forest fire
- an engineer checks a steel weld for cracks inside the metal
- a television signal is sent down to homes from a satellite in orbit

Which row gives the region used for each job?

Accepted Answer

B: infrared · X-rays · microwaves. Hot objects emit infrared, which thermal cameras detect even through smoke. X-rays pass through the steel and show internal cracks. Communication with satellites, including satellite television, uses microwaves.

Question 3

Two walkie-talkies are used on a ski slope. Each sends and receives radio waves of frequency 446 MHz.
A student writes three statements.

1 In the transmitting aerial, electrons oscillate at 446 MHz and produce the radio waves.
2 In the receiving aerial, the radio waves induce an alternating current of frequency less than 446 MHz, because some energy is lost on the way.
3 Visible light can be emitted when electrons in atoms change energy, and gamma rays can be emitted when a nucleus changes energy.

Which statements are correct?

Accepted Answer

B: 1 and 3 only. An alternating current (oscillating electrons) at 446 MHz in the transmitting aerial produces radio waves of 446 MHz (1 ✓). The waves induce an alternating current of the same frequency in the receiving aerial; losing energy makes the signal weaker (smaller amplitude), not lower in frequency (2 ✗). Changes of energy of electrons in atoms emit light, and changes in nuclei emit gamma rays (3 ✓).

	drone camera	steel weld	satellite television
A	infrared	ultraviolet	radio waves
B	infrared	X-rays	microwaves
C	ultraviolet	X-rays	radio waves
D	visible light	X-rays	microwaves