Reflection, Refraction and Lenses

All waves can be reflected.

- Sound waves reflect off walls and buildings. This is called an echoe. 

- Dolphins/bats use ultrasound (echolocation) to monitor their surrondings.

- Radio waves reflect from surfaces within the atmosphere like the ionsphere. 

Light waves will reflect from shiny surfaces following the laws of reflection:

- The angle of incidence = the angle of reflection

- The incident ray, the reflected ray and the normal line are all in the same plane. 

If asked to measure an angle, measure it from the normal to the ray. 

Refraction is the bending of light rays at a surface. Happens when entering/leaving a glass block.

When light travels from air to glass, the direction of the ray bends towards the normal. The angle of incidence is bigger than the refraction angle.

All waves are refracted at the boundary between different materials.

Refraction happens as the speed of the wave changes as it passes through different materials.

The speed of light depends on the density of the material. 

Less dense material -> more dense material = slower, causing a bend towards normal.

More dense material -> less dense material = faster, causing a bend away from normal.

Converging lens: Also known as convex lense, it is fatter in the middle.

- Used to form images in telescopes, cameras and binoculars.

- Rays of light that are parallel to the principal axis of a convex lense are refracted inwards.

Diverging lens: Also known as concave lense, is thinner in the middle. 

- The fatter the lense, the shorter the focal length.

- The distance between the centre of the lens and the focal point is the focal length.