Light is composed of electromagnetic waves. What are electromagnetic waves like?
Magnetic field
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A magnetic field is the region around a magnet in which a magnetic force can be experienced. If an iron nail is placed near a magnet in its magnetic field, the nail will experience a force of attraction.
Magnetic fields cannot be seen, but they can be 'felt' by objects made of iron or by other magnets.
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The shape of a magnetic field can be illustrated by iron filings sprinkled around the end of a magnet. The iron filings take the shape of the magnetic field.
If a bar magnet is held in the hand and vibrated up and down rapidly, then the magnetic field around the end of that magnet will also vibrate up and down. Ripples or waves in the magnetic field will be sent out from the magnet, like waves in a hose pipe that is being shaken up and down. |
Electric fields
An electric charge is what you feel when you get an electric shock. Around an electric charge is an electric field.
An electric field is the region around an electric charge in which an electric force can be experienced. If another charge is placed in that field, it will experience an electric force.
If an electric charge is held and vibrated from side to side rapidly, then the electric leading field around the charge will also vibrate from side to side. Ripples or waves in the electric field will be sent out from the charge, like waves in a hose pipe being shaken from side to side. If a magnet and an electric charge are held close together, and the magnet is vibrated up and down, and the charge is vibrated from side to side, waves in both the magnetic and electric fields will be produced. These will travel together away from the source of vibrations.
Electromagnetic waves
Electromagnetic waves are a combination of electric and magnetic waves. They always vibrate at right angles to each other as they travel.
If the rate of vibrations is fast enough, say 5 × 1014 vibrations per second, then these electromagnetic waves will affect the eyes, and they will be seen as light waves.
Colours
Different colours of light have electromagnetic waves that vibrate at different frequencies. For example, red light has a frequency of about 4.3 × 1014 vibrations per second. Blue light has a frequency of about 7.0 × 1014 vibrations per second.
Light as particles (the quantum model)
Most of the properties of light (eg reflection, refraction, dispersion and diffraction) can be explained using the model of electromagnetic waves. However, certain other properties of light, such as the photoelectric effect and line spectra, require an addition to the model called the particle or quantum model. A rainbow is a continuous spectrum of colours which blend into each other. A line spectrum consists of separate lines of colour with spaces between the lines.
In this model it is believed that the electromagnetic waves travel not as continuous waves, but as small bundles of electromagnetic waves often called 'photons'. In this model, light appears to have some of the properties of particles like bullets from a machine gun.
