The Electromagnetic Spectrum: Answers

List the types of radiation in the electromagnetic spectrum from the lowest frequency to the highest frequency.

The order of the different waves in the EM spectrum from the lowest frequency to the highest is: radio waves, microwaves, infra-red, visible light, ultraviolet, x-ray and gamma. Use a mnemonic to help you remember if you are struggling to memorise the order.

Are EM waves classed as transverse or longitudinal?

All electromagnetic waves are transverse. This means that the vibrations occur at right angles (perpendicular) to the direction of wave travel.

Gamma radiation is used in hospitals even though it can be dangerous. Describe one use of gamma radiation in hospitals.

Gamma radiation is useful because it kills microorganisms so it is used for sterilising equipment before an operation. It also kills cancer cells so is used as part of radiotherapy treatments for cancer. It can also be used as a radioactive tracer for the detection of cancer. You’ll learn more about radioactive tracers in the topic about radioactivity.

Explain the risk to patients and doctors of using gamma radiation.

The dangers of gamma radiation is that it can penetrate cells easily and mutate the DNA inside, leading to cancer. In general, the higher the energy (or frequency) of the radiation, the more harmful it is. Gamma radiation has the highest energy of all the different types of radiation in the EM spectrum and care needs to be taken when near to gamma-emitting sources. For the patient, who will be exposed for a short amount of time, the risk is much lower compared to the doctor, who will be continually exposed as part of his job.

State one way of reducing the risks to a doctor who uses gamma radiation.

The doctor should limit the amount of time exposed to the radiation and maintain a reasonable distance between themselves and the source of gamma rays.

Name two types of EM waves that are used for communications.

The two most obvious types of EM waves used in communications are radio waves, which are used for TV and radio broadcasting and micro waves which are used for mobile phone communications. You could also say visible light because it is used in optical fibre communications or infrared which is used to transmit information from remote controls.

Name two types of EM waves that are used for cooking.

The only types of EM waves which are used for cooking are microwaves (in microwave ovens - the clues in the name) and infra-red. Remember that infra-red radiation is the same thing as heat so this type of radiation is used in ovens, toasters, grills, deep-fat fryers and any other appliance that uses heat to cook food.

Ultrasound waves are used in hospitals to produce an image of a fetus. Ultraviolet waves are used by doctors to cure some skin conditions. Suggest two differences between ultrasound and ultraviolet waves.

Ultrasound is a longitudinal wave (its vibrations move parallel to the direction of wave travel) whereas ultraviolet waves are transverse (its vibrations move perpendicular to the direction of wave travel). Ultraviolet radiation is an electromagnetic wave, which do not need particles to transfer information/energy so they can travel in a vacuum. Ultrasound is not an EM wave and it requires particles to move from one point to another.

Those are the two most obvious differences but you can also mention that ultrasound travels more slowly than UV, which travels at the speed of light (remember that all EM waves travel the same speed through a vacuum). Finally, ultraviolet waves have a higher frequency than ultrasound waves.