Uses and dangers of EM waves: the practical uses of each group, the harm high-frequency waves can cause to cells, and how the use links to the wave's properties.

What this dot point is asking

Edexcel wants you to recall the practical uses of each group of the electromagnetic spectrum, to explain the dangers of the high-frequency (ionising) waves to the human body, and to link each use to the properties of that part of the spectrum.

Uses across the spectrum

Each use exploits a property of that part of the spectrum. Microwaves are absorbed by water in food (heating it) and pass through the atmosphere (so they reach satellites). Infrared is strongly absorbed and emitted by surfaces, making it ideal for heating and thermal cameras. X-rays pass through soft tissue but are absorbed by bone, which is why they image the skeleton.

Linking use to properties

When an exam asks "why is this wave used for this", connect the answer to a property. Optical fibres use visible light (and infrared) because it can be totally internally reflected along the fibre; gamma rays sterilise equipment because their high energy kills bacteria. Always justify a use by the wave's behaviour, not just by naming it.

Dangers of high-frequency waves

The danger increases towards the gamma end because the energy per wave increases with frequency. Ionising radiation can change or kill living cells, so exposure must be limited. Microwaves can also heat body tissue (internal heating) and excessive infrared can burn the skin, but the most serious cell-level damage comes from the ionising, high-frequency waves.

Precautions

How Edexcel examines this

This dot point is examined on both tiers, usually as a "state a use and explain why" question and a "dangers and precautions" question. For uses, the mark scheme rewards a correct use of the named wave plus a reason linking it to the wave's behaviour, so always add the "because" (microwaves are absorbed by water; X-rays are absorbed by bone; infrared is absorbed and emitted by surfaces). For dangers, examiners reward connecting the high frequency and energy of ultraviolet, X-rays and gamma rays to ionisation and damage to cells or DNA, with consequences such as cancer, and a valid precaution such as lead shielding or sunscreen. A frequent trap is treating microwaves as ionising; they cause internal heating but are not ionising. You may also be asked to compare the relative dangers across the spectrum, where the key idea is that the risk rises with frequency towards the gamma end. Linking the ionising nature of gamma rays here to the radioactivity topic strengthens an answer.

Try this

Q1. State one use of microwaves and the property that makes it suitable. [2 marks]

• Cue. Cooking food (microwaves are absorbed by water in the food, heating it), or communication (they pass through the atmosphere).

Q2. State why X-rays and gamma rays are harmful to cells. [1 mark]

• Cue. They are ionising (high energy), so they can damage cells and DNA.