Electromagnetic Spectrum (Oxford AQA IGCSE Combined Science Double Award)
Revision Note
Electromagnetic Spectrum
Electromagnetic waves are defined as:
Transverse waves that transfer energy from the source of the waves to an absorber
All electromagnetic waves share the following properties:
They are transverse
They can travel through a vacuum
They travel at the same speed in a vacuum
They transfer energy
There are 7 types of electromagnetic waves, grouped by energy, wavelength and frequency, which together form a continuous spectrum
The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies
The order of the groups within the electromagnetic spectrum, from the lowest frequency (longest wavelength), is:
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
The wavelengths range from radio waves with a wavelength of m to gamma rays with a wavelength of m and beyond
The electromagnetic spectrum
The relationship between the frequency and wavelength of waves across the electromagnetic spectrum is:
The higher the frequency, the shorter the wavelength
The lower the frequency, the longer the wavelength
This means that radio waves have a lower frequency and a longer wavelength than UV waves
This can be seen from the wave equation
Where:
= speed of the wave in metres per second (m/s)
= frequency of the wave in hertz (Hz)
= wavelength of the wave in metres (m)
Since all electromagnetic waves travel at the speed of light in a vacuum, speed is constant
Therefore, in the equation, in keeping v constant, if f increases then λ must decrease
Relationship between wavelength and frequency
The higher the frequency, the more energy the wave transfers
Worked Example
One region of the electromagnetic spectrum has wavelengths in the range to . The wave speed of electromagnetic waves is .
Calculate the maximum frequency of this region of the electromagnetic spectrum.
Answer:
Step 1: Deduce the wavelength which would have the maximum frequency within this range
The maximum frequency will have the shortest wavelength
The shortest wavelength in this region is
Step 2: List the known quantities
Wavelength,
Wave speed,
Step 3: Write out the equation relating wave speed, frequency and wavelength
Step 4: Rearrange for frequency and calculate the answer
Examiner Tip
If you are not sure which wavelength would give the maximum frequency, you could calculate the frequency for both the shortest and longest wavelength to see which one gives the maximum value.
Visible Light
Visible light is one small part of the electromagnetic spectrum
It is the part that we can detect with our eyes
The colours that our eyes see are dependent on the wavelength (or frequency) of the detected light
Red light has the longest wavelength and lowest frequency
Violet light has the shortest wavelength and highest frequency
The spectrum of visible light
Wavelength and frequency are inversely proportional, this means that:
An increase in wavelength is a decrease in frequency (towards the red end of the spectrum)
A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)
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