During this investigation I will be doing an experiment to find out how the thickness of a converging lens affects its focal length. A converging lens is convex; this means it gets bigger towards the middle of the lens. As such it causes the rays of light, which are refracted when they hit it, to converge at a focus. All lenses have a principal axis; this is a line that passes through the centre of the lens. Also all lenses have a focal point; this is where the rays that were initially parallel to the principal axis meet after being refracted by the lens. All lenses have two focal points, one is in front of the lens and one is behind the lens. The focal length of a lens is the distance between the middle of the lens and its focal point. The focal length of a lens is related to its power. The more powerful a lens is, the stronger it will converge the parallel rays of light and so the focal length will be shorter. PowerD=1focal length (m) The more curved the surface of the lens the more powerful the lens will be.
This diagram depicts some of the concepts I have just discussed.
Converging lenses use refraction to focus light waves to form an image of an object. The speed of a wave is affected by the density of the material it is travelling through. For example, light usually travels slower in more dense materials. This means that when a wave crosses a boundary between two different materials (e.g. glass to air) it changes speed. Wave Speed=frequency x wave length, as the wave length is fixed for each type of wave, if the frequency changes, the wavelength must also change. This means that the change in speed and wavelength can cause the wave to change direction, this is refraction. As a light ray hits the surface of a lens it passes from air to glass and so it slows down. This causes the light ray to bend or “refract” towards the normal. When it passes from glass to air on the other side the light speeds up and bends away from the normal. The...