This mini-lesson walks you through the whole of Eduqas Topic 6 — Light and electromagnetic waves: the EM spectrum, how each region interacts with matter (uses & dangers), lenses and ray diagrams, why objects look coloured, and black body radiation.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you're ready.
EM waves are all transverse waves made of oscillating electric and magnetic fields, so they need no particles to travel. In a vacuum they all travel at the same speed — the speed of light, 3 × 10⁸ m/s.
Watch out: a common slip is to think gamma rays "travel fastest". They don't — in a vacuum every EM wave travels at the same speed. Gamma rays have the highest frequency and energy, not the highest speed.
Because speed is fixed, as frequency rises the energy rises too — so each region behaves differently and is useful for different jobs:
Dangers: UV, X-rays and gamma have very short wavelength and high energy, so they are ionising — they can damage cells and cause mutations (cancer). UV ages skin and raises skin-cancer risk; this is why we use lead aprons and sun protection.
Tap a region on the left, then tap its main use on the right.
At a plane (flat) surface the law of reflection holds: the angle of incidence = angle of reflection, both measured from the normal.
The surface still obeys i = r for each tiny ray in diffuse reflection — it's the roughness that scatters parallel rays in different directions.
A lens refracts light to form an image. A ray through the centre of a lens carries straight on.
Watch out: a converging (convex) lens can make a real OR a virtual image — it depends on where the object sits. Closer than one focal length it acts as a magnifying glass (virtual image); further away it forms a real image.
When the object is beyond the focal point, two rays locate the image:
A real image is where light rays actually cross, so it can be caught on a screen.
A concave (diverging) lens always makes the same kind of image, wherever the object is: virtual, upright and diminished. The rays only appear to come from a point in front of the lens.
Virtual means no light actually meets there, so it cannot be projected onto a screen — your eye just sees it.
Magnification compares the size of the image with the size of the object:
It has no units because it is a ratio of two lengths. If m > 1 the image is magnified; if m < 1 it is diminished.
A 4 mm tall object forms a 12 mm tall image.
m = 12 ÷ 4 = 3 (the image is 3× the object's height).
White light contains every frequency (colour) of the visible spectrum. When it hits an opaque object some frequencies are absorbed and the rest are reflected — and the reflected ones reach your eye.
Materials are described as transparent (all light transmitted, e.g. clear glass), translucent (only some transmitted, the rest scattered/absorbed) or opaque (none transmitted). A colour filter transmits its own colour and absorbs the rest.
Watch out: a red object does not "turn light red". It reflects the red already present in white light and absorbs the rest. Under pure blue light a red object looks black — there's no red for it to reflect.
Every object both emits and absorbs EM radiation (mainly infrared). The hotter the surface, the more intense the radiation and the shorter its peak wavelength.
A perfect black body is an idealised object that absorbs all radiation falling on it (reflecting and transmitting none). Because a good absorber is a good emitter, it is also a perfect emitter. Stars are the closest real things to black bodies.
Watch out: "good absorber = good emitter." A matt black object isn't only good at soaking up radiation — it is equally good at radiating it away. That's one object, two skills.
Earth's temperature depends on the balance between the radiation it absorbs (mostly from the Sun) and the radiation (mostly infrared) it emits back into space:
Tap a statement, then tap whether Earth's temperature would rise or fall.
EM order (↑freq): radio · micro · IR · visible · UV · X-ray · gamma
Speed: all the same in a vacuum = 3 × 10⁸ m/s
Ionising & harmful: UV, X-rays, gamma
Lenses: convex = converging (real OR virtual); concave = diverging (always virtual)
Magnification: m = image height ÷ object height
Colour: reflect own colour, absorb the rest; filters transmit one colour
Black body: good absorber = good emitter; Earth's temp = absorb vs emit balance
You've covered all of Eduqas Topic 6 — the spectrum, interactions, lenses, colour and black body radiation. Press Finish to see your score.
You've worked through Light and Electromagnetic Waves for Eduqas GCSE Physics. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.