Level 7: Lenses and telescopes

Waves, sound and light · level 7 of 8 · rough age 15-16 (a guide for parents; anyone can start anywhere)

This level bends light on purpose. You use Snell's law and total internal reflection, then lenses: focal length, ray diagrams and the lens equation. You build a telescope from two lenses, point it at Mars, and finish by working out how the camera on a Mars orbiter photographed the Earth and Moon from 142 million km away.

Lesson	You will be able to
Refraction and Snell's law	Use \(n_1 \sin\theta_1 = n_2 \sin\theta_2\) and find a critical angle
Converging lenses	Draw ray diagrams and find the power of a lens
The lens equation	Use \(1/f = 1/u + 1/v\) and find the magnification
Telescopes	Find a telescope's magnification, and explain why a big aperture helps
Seeing Mars from Earth	Work out how big Mars looks through a telescope
Seeing Earth from Mars	Use angular resolution to explain a Mars orbiter's photos

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