Edexcel IGCSE Physics 复习笔记 3.1.5 Electromagnetic (EM) Waves
Edexcel IGCSE Physics 复习笔记 3.1.5 Electromagnetic (EM) Waves
Properties of EM Waves
- 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 all transverse
- They can all travel through a vacuum
- They all travel at the same speed in a vacuum
- There are 7 types of electromagnetic waves, which all together form a continuous spectrum
The EM Spectrum
- The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies
- This order is shown in the diagram below from longest wavelength (lowest frequency) to shortest wavelength (highest frequency)
Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum
- The higher the frequency, the higher the energy of the radiation
- Radiation with higher energy is:
- Highly ionising
- Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
- Radiation with lower energy is:
- Useful for communications
- Less harmful to humans
Visible Light
- Visible light is defined as the range of wavelengths which are visible to humans
- Visible light is the only part of the spectrum detectable by the human eye
- However, it only takes up 0.0035% of the whole electromagnetic spectrum
- In the natural world, many animals, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light
- Each colour within the visible light spectrum corresponds to a narrow band of wavelength and frequency
- The different colours of waves correspond to different wavelengths:
- Red has the longest wavelength (and the lowest frequency and energy)
- Violet has the shortest wavelength (and the highest frequency and energy)
The colours of the visible spectrum: red has the longest wavelength; violet has the shortest
- 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)
Exam Tip
See if you can make up a mnemonic to help you remember the EM spectrum!One possibility is:
Raging Martians Invaded Venus Using X-ray Guns
To remember the colours of the visible spectrum you could remember either:
- The name “Roy G. Biv”
- Or the saying “Richard Of York Gave Battle In Vain”
You could even combine both to have a mega mnemonic:
Raging Martians Invaded Roy G. Biv Using X-ray Guns!
The electromagnetic spectrum is usually given in order of decreasing wavelength and increasing frequency i.e. from radio waves to gamma waves
Remember:
- Radios are big (long wavelength)
- Gamma rays are emitted from atoms which are very small (short wavelength)
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