Electromagnetic Waves
Electromagnetic waves are transverse waves with different frequencies that make up the electromagnetic spectrum. The waves are created by the oscillation of electric and magnetic fields that are perpendicular to each other. The fields are also perpendicular to the direction of the wave travel.
All electromagnetic waves share a couple of common properties:
- Don’t need a medium to propagate – they can travel through a vacuum
- Travel at the speed of light in a vacuum
The electromagnetic spectrum is split into seven groups. At one end of the spectrum we have gamma rays. These have the shortest wavelength (highest frequency) and the most energy. As we move to the opposite end of the spectrum wavelength increases (frequencies decrease) and the energy decreases. This ends with radio waves that have the longest wavelength, lowest frequency, and the least energy.
The diagram below shows how the spectrum is split:
IMPORTANT NOTE: These divisions are not exact. There is overlap between the categories and it quite often depends how the waves are produced that determines their type – not a specific wavelength.
Gamma Rays
Typical Wavelengths: 10-16 – 10-10 m
Typical Frequencies: 1024 – 1018 Hz
Production: Nuclear decay (they can also be produced in nuclear accelerators).
Gamma rays can be used in the diagnosis and treatment of cancers. They are, however, ionising (the most ionising electromagnetic wave) and can cause mutations in genes that can lead to cancer.
X-Rays
Typical Wavelengths: 10-12 – 10-8 m
Typical Frequencies: 1020 – 1016 Hz
Production: Emitted when high energy electrons hit metal targets.
X-rays are used for internal imaging of the body and to analyse crystal structures. Like gamma rays, X-rays are a form of ionising radiation and can also cause cell mutations.
Ultraviolet
Typical Wavelengths: 10-9 – 10-7 m
Typical Frequencies: 1017 – 1014 Hz
Production: Produced from high temperature solids and gases.
Higher energy UV waves are a form of ionising radiation and like gamma rays and x-rays can cause damage to cells. Ultraviolet radiation is emitted by the Sun and can cause the skin to tan or burn as well as cause damage to eyes. UV light can be used to detect counterfeit money and it is also absorbed by fluorescent substances that re-emit the energy as visible light.
Visible Light
Typical Wavelengths: 3.7 x10-7 – 7.4 x10-7 m
Typical Frequencies: 1014 – 1014 Hz
Production: Produced from high temperature solids and gases.
These are the light waves that we can see. The spectrum of visible light starts with violet (the shortest wavelength, highest frequency) and ends with red (the longest wavelength, lowest frequency). The combination of all the colours in the spectrum gives us white light. Visible light can also be used in fibre optic communication.
Infrared
Typical Wavelengths: 10-7 – 10-3 m
Typical Frequencies: 1014 – 1011 Hz
Production: Any object with a temperature above absolute zero emits infrared radiation.
There are many uses of infrared such as night vision cameras, heaters and remote controls. It can also be used to identify chemical substances via infrared spectroscopy.
Microwaves
Typical Wavelengths: 10-4 – 10-1 m
Typical Frequencies: 1012 – 109 Hz
Production: Produced by a magnetron.
The practical uses of microwaves are cooking and communications. Microwaves that have a high frequency can be absorbed by molecules. This increases their internal energy which increases their heat – this cooks food molecules.
Radio Waves
Typical Wavelengths: 10-1 – 104 m
Typical Frequencies: 109 – 104 Hz
Production: Oscillations in electric circuits.
Radio waves can easily be transmitted through air and so are widely used for communication (television and radio).
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