The Electromagnetic Spectrum — The Order, the Uses and the Discoverers

One Family, Seven Names

An electromagnetic wave is an oscillating electric field and an oscillating magnetic field travelling together, at right angles to each other and to the direction of travel. Two properties matter for exams:

1. 1.No medium is needed. EM waves cross empty space, which is why sunlight reaches us and sound does not.
2. 2.In vacuum, every one of them travels at the same speed — about 3 × 10⁸ metres per second. Radio waves are not slower than gamma rays. This single sentence is the most frequently missed fact in the whole chapter.

They are linked by c = νλ (speed = frequency × wavelength), so frequency and wavelength move in opposite directions: the shorter the wave, the higher the frequency. Energy follows frequency through E = hν, so the shortest waves also carry the most energy.

The seven names are not seven different things. They are one continuous spectrum, sliced up and labelled by how we produce and use each band.

1. Which of the following electromagnetic waves has the highest frequency?

2. A television remote control works using which type of radiation?

3. In vacuum, how does the speed of radio waves compare with the speed of gamma rays?

4. X-rays were discovered by which scientist?

5. The ozone layer in the atmosphere mainly protects living beings by absorbing which radiation?

6. Which sequence arranges these waves in order of increasing wavelength?

7. The approximate wavelength range of visible light is:

8. A microwave oven heats food mainly because its radiation: