The Electromagnetic Spectrum: Question 2

Worked solution

Part (a): Comparing the speeds of two regions of the spectrum

Every region of the electromagnetic spectrum (radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays) is part of the same family of waves, and all of them travel at the same high speed through a vacuum. X-rays and radio waves sit at opposite ends of the spectrum (very short wavelength versus very long wavelength), but this does not affect their speed:

$\boxed{\text{X-rays and radio waves travel at the same speed through a vacuum}}$

This is one of the key recall facts for this topic: the regions differ in wavelength and frequency, but never in speed, when travelling through a vacuum.

Part (b): A use of microwaves

Microwaves are used for:

• cooking and heating food in a microwave oven (they are absorbed by water molecules in food, transferring energy as heat), or
• satellite communication and mobile phone signals.

Any one of these (or another correct microwave use) earns the mark.

Part (c): A use of infrared radiation

Infrared radiation is used for:

• remote controls for televisions and other devices, or
• thermal imaging cameras, which detect the infrared radiation emitted by warm objects (including the human body), or
• short-range wireless data links.

Any one correct use earns the mark.

Part (d): A harmful effect of ultraviolet radiation

Ultraviolet radiation carries enough energy to damage living cells. Acceptable harmful effects include:

• damage to skin cells, causing sunburn or premature ageing of the skin, and an increased risk of skin cancer, or
• damage to the eyes, including damage to the retina.

Final answers

• (a) Speed of X-rays compared with radio waves $=$ the same (both travel at the same speed through a vacuum)
• (b) Use of microwaves $=$ e.g. cooking food / satellite communication
• (c) Use of infrared $=$ e.g. remote controls / thermal imaging
• (d) Harmful effect of ultraviolet $=$ e.g. skin damage / skin cancer / eye damage