4 mistakes learners make with the electromagnetic spectrum, each one named and explained.
The spectrum is one family of waves. They differ in wavelength and frequency, and in nothing else.
You say radio waves from a phone mast are dangerous in the same way as gamma rays, or that none of it is a risk at all.
The word radiation is used in the news almost only when something is dangerous.
Question. Which is more dangerous to living cells, a radio wave or an ultraviolet ray?
A common answer. both the same, they are both radiation
The answer. ultraviolet, because it carries enough energy to ionise
Why. Danger rises with frequency. Radio, microwave, infrared and visible are not ionising; ultraviolet, X-rays and gamma are.
Place it on the spectrum first. Where it sits is what decides the risk.
You say you can see infrared coming off a hot grill or a radiator.
Something hot enough really does glow, and the glow and the heat arrive together.
Question. Can you see infrared radiation?
A common answer. yes, it is the orange glow of something hot
The answer. no. The glow is visible light; the infrared alongside it is invisible
Why. Infrared sits beyond red, outside the range the eye can detect, which is why cameras are needed to image it.
If your eye is detecting it, it is visible light by definition.
You describe light as made of rays, or say covering half a lens cuts the image in half because half the rays are gone.
Every diagram draws light as a few neat arrows, and the arrows are the only part you ever see on paper.
Question. Half of a lens is covered. What happens to the image?
A common answer. half the image disappears
The answer. the whole image stays, but it gets dimmer
Why. Light from every point of the object reaches every part of the lens, so the uncovered half still forms a complete image.
Rays are a drawing tool. Ask what the light is actually doing, not what the arrows show.
You describe radio waves, light and gamma rays as three unrelated kinds of thing that happen to be listed together.
They are met in different lessons, they are used for different jobs, and only one of them can be seen.
Question. What is the difference between a radio wave and a gamma ray?
A common answer. they are completely different kinds of thing
The answer. only their wavelength and frequency
Why. All of them are the same kind of wave and all travel at the same speed in a vacuum.
Name the wavelength. That is the only thing that changes along the spectrum.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.