Electromagnetic Spectrum (Oxford AQA IGCSE Physics)

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

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)