AQA Combined Science (8464) 6.6.2.1 · Model
Types of electromagnetic waves
Radio waves, light and gamma rays are the same kind of wave. What changes from one end of the spectrum to the other, and what never changes?
Combined Science · Higher tier
Start here
Your phone is sending a wave to the nearest mast right now.
The phone signal, the warmth you feel from a fire, the light from this screen, the ultraviolet that tans skin and the X-rays that photograph a broken bone are one family of waves: electromagnetic waves.
If you had to guess, can your eyes detect most of that family, or only a small part of it?
Every group in the spectrum is the same kind of wave. Electromagnetic waves are transverse: the oscillations are at right angles to the direction the energy travels. They transfer energy from a source to an absorber, and they need no material to travel through, so they cross the vacuum of space. Together they form one continuous spectrum, grouped by wavelength (the distance from a point on one wave to the same point on the next wave) and frequency (the number of waves passing a point each second). You know where visible light sits. Can you place the other six?
The spectrum bench · part 1 of 2
Build the spectrum
Tap the seven groups in order, longest wavelength first. Tap a placed group to take it back.
Energy transfer · source to absorber
The Sun on your face
On a cold, clear day you can still feel the Sun warm your face. Put the energy transfer in order.
4 links belong. 2 do not.
The links
Your chain · 0 of 4
Equations
The bench showed it: at one fixed speed, shorter waves mean more waves every second. The wave equation says exactly that.
v = f λ
wave speed (v, metres per second) = frequency (f, hertz) × wavelength (λ, metres)
f = v ÷ λ · λ = v ÷ f
The speed
Any electromagnetic wave in a vacuum or air: v = 3 × 10⁸ m/s, which is 300 000 000 m/s. The question gives you this value.
Units first
Frequency in Hz: kHz × 1000, MHz × 1 000 000, GHz × 1 000 000 000. Wavelength in m: km × 1000, cm ÷ 100.
Command words in this lesson
- Give
- A short answer. No reason is needed.
- Complete
- Fill the blank boxes of the spectrum, in order.
- Calculate
- Show the working. The unit earns its own mark.
- Explain
- Link each idea to the next with “so” or “because”.
- Describe
- Say what it is like, accurately, in order. No reasons needed.
Key fact
From radio waves to gamma rays the wavelength gets shorter and the frequency gets higher. The speed in a vacuum never changes.
Key note · AQA 6.6.2.1 (8464)
Types of electromagnetic waves
- EM spectrum (long→short λ): radio, microwave, infrared, visible, UV, X-ray, gamma.
- All travel at 3×10⁸ m/s in vacuum.
- All transverse.
- Higher frequency = shorter λ.
- Visible: red (longest) to violet (shortest).
- Our eyes detect only visible light.
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
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Ask MrBadmus
Not sure which way wavelength and frequency change across the spectrum?
The waves on the bench are drawn to show which is longer, not to scale: real wavelengths run from kilometres for radio waves to far smaller than an atom for gamma rays. On screen every wave moves at the same slow speed, as all electromagnetic waves share one speed in a vacuum; the real speed is 3 × 10⁸ m/s. The groups have no sharp edges: neighbouring groups merge into each other.