Physics · Rung 13 of 23

Light

Light travels in straight lines while nothing stops it, and that is what gives shadows an edge. When it hits a mirror it leaves at the same angle it arrived at, on the other side of the normal: that is why a mirror gives back an ordered image and not a smear. When it passes from air into water it bends, because it travels slower in water, and that is why a stick in water looks broken right at the surface and a fish appears where it is not.

Where this sits

Comes after
Waves

Exercises from this rung

Generated by the app, from easiest to hardest

  1. An object 100 cm tall is 3 m from a wall, with a lamp right behind it. How big is its shadow?

    • 4 m
    • 1 m
    • 5 m
    • 3 m

    Why Rays leave the lamp in straight lines and spread: at 4 times the distance, the shadow is 4 times the object. Light travelling straight is what gives shadows an edge, and what made sundials work.

    easier

  2. An object 50 cm tall is 2 m from a wall, with a lamp right behind it. How big is its shadow?

    • 1.5 m
    • 2 m
    • 0.5 m
    • 1 m

    Why Rays leave the lamp in straight lines and spread: at 3 times the distance, the shadow is 3 times the object. Light travelling straight is what gives shadows an edge, and what made sundials work.

    in between

  3. How fast does light travel in a vacuum?

    • 30,000 km/s
    • 3,000 km/s
    • 3 million km/s
    • 300,000 km/s

    Why Three hundred thousand kilometres per second: seven and a half times around the Earth in one second. Even so it takes eight minutes to arrive from the Sun, so what we see of the Sun is always the Sun of eight minutes ago.

    harder