Features of Electromagnetic Waves
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This diagram shows the key features of electromagnetic (light) waves and introduces some of the terms used to describe them.
- Across the centre is an electromagnetic wave, shown in red.
- The wave is travelling from left to right.
- The different features of the wave are shown by labels.
- At the bottom of the diagram are short definitions of key terms.
Description
Features of Electromagnetic Waves
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About the diagram
About the diagram
- This diagram shows the key features of electromagnetic (light) waves and introduces some of the terms used to describe them.
- Across the centre is an electromagnetic wave, shown in red.
- The wave is travelling from left to right.
- The different features of the wave are shown by labels.
- At the bottom of the diagram are short definitions of key terms.
Remember that:
- Electromagnetic radiation (light) is often described in terms of waves.
- Electromagnetic waves, which are a form of electromagnetic radiation, propagate from a light source, travel through space, and encounter different materials.
- Visible light corresponds with the range of wavelengths of electromagnetic radiation that are responsible for the sense of sight.
- Visible light is a form of electromagnetic radiation, as are radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves.
- The range of wavelengths that produce visible light forms a very small part of the electromagnetic spectrum.
- Visible light is perceived as colour. The colour red has been chosen to correspond with the wavelength of this wave.
Some key terms
Wavelength is the distance from any point on a wave to the corresponding point on the next wave. This measurement is taken along the middle line of the wave.
- While wavelength can be measured from any point on a wave, it is often simplest to measure from the peak of one wave to the peak of the next, or from the bottom of one trough to the bottom of the next, ensuring the measurement covers a whole wave cycle.
- The wavelength of an electromagnetic wave is usually given in metres.
- The wavelength of visible light is typically measured in nanometres, with 1,000,000,000 nanometres making up a metre.
- Each type of electromagnetic radiation – such as radio waves, visible light, and gamma waves – corresponds to a specific range of wavelengths on the electromagnetic spectrum.
In physics and optics, a medium refers to any material through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.
- Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
- The properties of the medium, such as its density and composition, influence how light propagates through it.
- Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
- Examples of Mediums:
- Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
- Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
- Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.
An electromagnetic wave carries electromagnetic radiation.
- An electromagnetic wave is formed as electromagnetic radiation propagates from a light source, travels through space and encounters different materials.
- Electromagnetic waves can be imagined as synchronised oscillations of electric and magnetic fields that propagate at the speed of light in a vacuum.
- Electromagnetic waves are similar to other types of waves in so far as they can be measured in terms of wavelength, frequency and amplitude.
- We can feel electromagnetic waves release their energy when sunlight warms our skin.
- Remember that electromagnetic radiation can be described either as an oscillating wave or as a stream of particles, called photons, which also travel in a wave-like pattern.
- The notion of waves is often used to describe phenomena such as refraction or reflection whilst the particle analogy is used when dealing with phenomena such as diffraction and interference.
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The speed (or velocity) of a light wave is a measurement of how far it travels in a certain time.
- The speed of light is measured in metres per second (m/s).
- Light travels through a vacuum at 300,000 kilometres per second.
- The exact speed at which light travels through a vacuum is 299,792,458 metres per second.
- Light travels through other media at lower speeds.
- A vacuum is a region of space that contains no matter.
- Matter is anything that has mass and occupies space by having volume.
- When discussing electromagnetic radiation the term medium (plural media) is used to refer to anything through which light propagates including empty space and any material that occupies space such as a solid, liquid or gas.
- In other contexts empty space is not considered to be a medium because it does not contain matter.
The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time.
- Frequency is measured in Hertz (Hz) and signifies the number of wave-cycles per second. Sub-units of Hertz enable measurements involving a higher count of wave-cycles within a single second.
- The frequency of electromagnetic radiation spans a broad range, from radio waves with low frequencies to gamma rays with high frequencies.
- The wavelength and frequency of light are closely linked. Specifically, as the wavelength becomes shorter, the frequency increases correspondingly.
- It is important not to confuse the frequency of a wave with the speed at which the wave travels or the distance it covers.
- The energy carried by a light wave intensifies as its oscillations increase in number and its wavelength shortens.
A wave-cycle is the complete up-and-down motion of a wave, from one crest (peak) to the next crest, or from one trough (dip) to the next trough. Visualize a wave cycle as a series of points plotted along the path of a wave from one crest to the subsequent crest.
- All electromagnetic waves have common characteristics like crests, troughs,, wavelength, frequency, amplitude, and propagation direction.
- As a wave vibrates, a wave-cycle can be seen as a sequence of individual vibrations, measured from one peak to the next, one trough to the next, or from the start of one wave cycle to the start of the next.
- A wave-cycle refers to the path from one point on a wave during a single oscillation to the same point on completion of that oscillation.
- Wavelength meanwhile, is a measurement of the same phenomenon but in a straight line along the axis of the wave.
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