The Electromagnetic Spectrum
Describe the full electromagnetic spectrum from radio waves to gamma rays, in order of increasing frequency and energy; explain that all EM waves travel at the same speed in a vacuum; and describe the uses and hazards of different regions
What a learner can do afterwards
- Lists the seven regions of the EM spectrum in order of increasing frequency
- States that all EM waves travel at 3 × 10⁸ m/s in a vacuum
- Gives at least one use and one hazard for each region of the spectrum
- Explains why some EM waves are more dangerous to living tissue than others (linked to frequency/energy)
The lesson
Light is only one member of a huge family of waves called the electromagnetic spectrum. Every member of this family travels through empty space at exactly the same speed: 3 x 10^8 metres per second (300,000,000 m/s). What makes each member different is its frequency, how many wave cycles pass a point every second.
A microwave oven uses microwaves to shake water molecules in your food and heat it up. A hospital X-ray machine uses X-rays, much higher up the spectrum, to pass through skin and show your bones. Both are electromagnetic waves moving at the same speed. The X-ray just carries far more energy in each wave.
Every region has jobs it's good at, and risks that come with it. Radio waves carry TV and phone signals with almost no risk to you. Ultraviolet light from the sun helps your skin make vitamin D, but too much gives you sunburn or skin cancer. Gamma rays can kill cancer cells in radiotherapy, but they can also damage healthy cells if you're overexposed.
Higher frequency means higher energy. Radio, microwave, and infrared waves mostly just warm things up gently. Ultraviolet, X-ray, and gamma waves carry enough energy to break bonds inside living cells, which is why doctors and radiographers wear shielding around them.
All seven regions of the electromagnetic spectrum travel at the same speed in a vacuum; the higher the frequency, the higher the energy, and the greater the risk to living tissue.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.