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 1 cross times 10 to the power of 4 m to gamma rays with a wavelength of 1 cross times 10 to the power of negative 15 end exponent m and beyond

The electromagnetic spectrum

EM spectrum, for IGCSE & GCSE Physics revision notes
The electromagnetic spectrum in order of decreasing wavelength and increasing frequency
  • 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

v space equals space f space cross times space lambda

  • Where:

    • v = speed of the wave in metres per second (m/s)

    • f = frequency of the wave in hertz (Hz)

    • lambda = 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

Frequency and wavelength, for IGCSE & GCSE Physics revision notes
The larger the wavelength, the lower the frequency. The speed remains the same
  • The higher the frequency, the more energy the wave transfers

Worked Example

One region of the electromagnetic spectrum has wavelengths in the range 1 cross times 10 to the power of negative 11 end exponent space straight m to 1 cross times 10 to the power of negative 9 end exponent space straight m. The wave speed of electromagnetic waves is 3 cross times 10 to the power of 8 space straight m divided by straight s.

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 1 cross times 10 to the power of negative 11 end exponent space straight m

Step 2: List the known quantities

  • Wavelength, lambda space equals space 1 cross times 10 to the power of negative 11 end exponent space straight m

  • Wave speed, v space equals space 3 cross times 10 to the power of 8 space straight m divided by straight s

Step 3: Write out the equation relating wave speed, frequency and wavelength

nu space equals space f space cross times space lambda

Step 4: Rearrange for frequency and calculate the answer

f space equals space nu over lambda

f space equals space fraction numerator 3 cross times 10 to the power of 8 over denominator 1 cross times 10 to the power of negative 11 end exponent end fraction

f space equals space 3 cross times 10 to the power of 19 space Hz space

Examiner Tips and Tricks

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

Spectrum of visible light, for IGCSE & GCSE Physics revision notes
Colours of the visible spectrum with increasing wavelength
  • 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)

    • decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)

Last updated:

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Leander Oates

Author: Leander Oates

Expertise: Physics

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

Caroline Carroll

Author: Caroline Carroll

Expertise: Physics Subject Lead

Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.