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Transcript
15.1 Lenses What is a lens? A contact lens Can you list out other applications of lenses? Lenses are used in telescopes microscopes cameras 15.1 Lenses Convex and concave lenses convex lenses thicker at the centre than at the edge concave lenses thinner at the centre than at the edge 15.1 Lenses What happens when parallel light rays pass through a convex lens? The rays converge to a single point. convex lens = converging lens 15.1 Lenses What happens when parallel light rays pass through a concave lens? The rays diverge and appear to come from a single point. concave lens = diverging lens 15.1 Lenses Terms used to describe convex lenses optical centre C optical centre – the centre of the lens 15.1 Lenses principal axis C principal axis – a straight line perpendicular to the lens and passing through the optical centre 15.1 Lenses principal focus F’ C F Rays passing through convex lens parallel to the principal axis converge to the principal focus. A convex lens has 2 principal foci. 15.1 Lenses F’ C F focal length f focal length – the distance between the focus and the optical centre 15.1 Lenses focal plane principal axis C F focal plane – a plane through the principal focus and is perpendicular to the principal axis. Simulation: Parallel rays through convex lens 15.1 Lenses Terms used to describe concave lenses principal focus principal axis F’ focal length f optical centre C F 15.1 Lenses C principal axis F’ focal plane Simulation: Parallel rays through concave lens 15.1 Lenses How lenses work Why does a convex lens converge light rays? Why does a concave lens diverge light rays? 15.1 Lenses Think of a convex lens as a number of prisms. The rays near the edge are refracted more. F When light rays leave the prisms, they are refracted away from the normal. When light rays enter the prisms, they are refracted towards the normal. 15.1 Lenses Think of a concave lens as a number of prisms. The rays near the edge are refracted more. F’ When light rays enter the prisms, they are refracted towards the normal. When light rays leave the prisms, they are refracted away from the normal. 15.1 Lenses Does the ray passing through the optical centre of a lens change direction? No. It is laterally displaced. larger lateral displacement smaller lateral displacement 15.1 Lenses That’s the end of Section 15.1 Check Point Key Ideas Previous Page Section 15.2 Exit