Lenses

Lenses

In glass prisms...

• In a rectangular prism, the ray bends towards the normal as it enters the denser medium, and away from the normal as it emerges into a less dense medium
• Different wavelengths of light refract by different amounts, white light disperses into different colours when it enters a prism
• A rectangular prism has parallel boundaries so the rays bend one way when they enter and the other way by the same amount when they leave - white light emerges
• With a triangular prism the boundaries aren't parallel so different wavelengths don't recombine, creating a rainbow effect

Different lenses produce different kinds of images:

• Two main types of lens - converging & diverging
• Converging lens is convex - bulges outwards, causing parallel light rays to converge to a focus
• Diverging lens is concave - caves inwards, causing parallel light rays to diverge
• The axis of a lens is a line passing through the middle of the lens
• The focal point of a converging lens is where the parallel lines hitting the lens meet
• The focal point of a diverging lens is the point where all the parallel rays that are hitting the lens appear to come from
• Each lens has a focal point in front and behind

Rules of refraction for a converging lens...

• An incident ray parallel to the axis refracts through the lens and passes through the focal point on the other side
• An incident ray passing through the focal point refracts through the lens and travels parallel…