The 7 types of EM waves
EM radiation occurs at many different wavelengths. In fact EM radiation is a continuous spectrum of these different wavelengths. Waves with similar wavelengths will have similar properties. Because of this, EM radiation is split into 7 different types of wave.
Radiowaves, Microwaves, Infrared, Visible light, Ultra-Violet light, X-rays, Gamma
Longest wavelength Shortest wavelength
Lowest frequency Highest frequency
Within each of these seven sections, the wavelengths still differ, for example, in the visible light part of the spectrum, each colour of light has a different frequency and wavelength e.g. blue has a shorter wavelength than red.
All types of EM radiation travel at exactly the same speed through space (a vacuum), which is around 300 million m/s (300,000,000 m/s).
Sound waves AREN'T part of the EM spectrum
- They are transmitted by vibrating particles, unlike EM radiation, and so are unable to travel through a vacuum (as there are no particles to travel through)
- This can be demonstrated by the Bell Jar experiment, where air is removed from the jar using a vaccum pump. As the air is removed, the bell gets quieter and quieter.
- However, within this experiment, the bell must be mounted on something such as foam to stop the sound from otherwise travelling through the solid surface which would make the base vibrate. If this happened, you'd still be able to hear it.
The energy of a photon
All EM radiation transfers energy. As well as acting as waves, EM radiation can also act as if it's made up of lots of really tiny particles. These particles are packets of energy, known as photons.
The energy that is delivered by each photon in a beam of EM radiation depends on the frequency of the EM waves.
The higher the frequency, the higher the energy the photon delivers.
The Intensity of a beam of radiation
The intensity (i.e. strength) of a beam of radiation = amount of energy delivered per second.
Within a beam of EM radiatoin of a particular frequency, each photon carries the same amount of energy, but this amount of energy depends on the frequency of the radiation.
Because of this, the intensity of a beam will depend on the number of photons arriving each second, and the energy of the photons in the beam.