Unit 3: Light and Optical Instruments

J. PulickeelJanuary 2007

Lesson 4: Concave and Convex Reflections

Reflecting on Reflections

• Reflections occur when light rays bounce off objects.

• We can predict the direction in which reflected light rays travel by using the laws of reflection

1. The angle of reflection will ALWAYS equal the angle of incidence

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

YAY!!! MIRRORS!!!!

Mirror, Mirror on the Wall

Concave and Convex

• A Concave Mirror is a mirror that is curved inwards (like the mouth of a cave)

• The bowl of a spoon is concave

• Convex mirrors are mirrors that bulge outward like the surface of a shiny balloon

Concave and Convex

Concave Chaos

• A concave mirror can change the attitude of your image. The attitude describes if the image is upright or upside down

Concave Chaos

• A concave mirror can also make the

image appear larger or smaller

• It depends on where the image is relative to the concave surface

Concave Chaos

Centre of Curvature

Focal Point

Radius

½ Radius

Object behind the Centre

• If the object is behind the centre of curvature, it will appear upside down and smaller

Click here for online activity

Object at the Centre

• If the object is at the centre of curvature, it will appear upside down but the same size

Click here for online activity

Object in front of the Centre

• If the object is in front of the centre of curvature, it will appear upside down and larger

Click here for online activity

Object in front of the Focal Point

• If the object is in front of the focal point, it will appear upright and larger

Click here for online activity

Convex Mirrors

• Convex mirrors are more common than concave mirrors. They always produce smaller upright images.

• Because the image is smaller you can see more of the overall scene

Convex Mirrors

• A convex mirror is just the other side of a concave mirror!

Click here for online activity

Concave Lenses

• A lens is a curved piece of transparent material .• A Concave lense is thinner and flatter in the

middle

• When light passes through the thicker more curved parts, it will bend more

A Convex lense is thicker and rounder in the middle

• This causes the refracting light rays to converge

In Summary

Regular Mirror All is good and happy and easy. Everyone loves a regular mirror

Concave Mirror

Image can be inverted (change in attitude) and the size can change

Convex Mirror More common than a concave mirror. Images appear upright and smaller. It is used on busses, in stores, etc…