Know how to identify the correct reflected ray from a plane mirror
(a) Roll a small ball on the floor so it hits the wall and bounces off at about 45 degrees. Repeat this for a number of different angles, without comment, and ask the students what they notice about how the ball bounces away and then to predict the direction that the ball will bounce off at. Consider what is meant by the term 'angle' and to predict the angle of relection of the ball Make the point that the aim of the activity is to think about light reflecting not bouncing balls. (b) Locate a projector in the middle of a room so that it casts a narrow beam of light across the lab. Switch off the lights and locate the beam. Ask students to predict where a mirror will reflect the beam to on the wall and then try out. Repeat with different mirror angles, establishing the idea that the more the angle is turned the greater the angle of relection. (c) Students working in pairs with ray boxes establish the idea that the 'angle going in is the same as the angle coming out' by using relection of the ray in plane mirrors and measuring with a protractor. Measure the angle from the mirror to the rays before and after the reflection.
Know how to apply understanding of angles of incidence and reflection
(a) Introduce the keyterms: 'incident ray' as the ray before reflection,'reflected ray' as the angle after reflection, 'the normal' as a theoretical line perpendicular to the mirror, 'angle of incidence' as the angle between the normal and incident ray, and 'angle of reflection' as the angle between the normal and the reflected ray. Concentrate on discriminating between these angles and those between the mirror and the rays. (b) Demonstrate the correct ray diagram construction of a reflection in a plane mirror on an OHP, but pause before drawing the reflected ray. Ask the students to predict the angle at which it should be drawn, refering to any earlier work with bouncing ball etc. Elicit from them that "the angle of reflection must be equal to the angle of incidence" and test using a ray box on the OHP that the theory is correct. (c) Students to work in pairs using ray boxes with slits to check if their predicted ray diagrams are correct.