"OHP and Mirror" Return to list of pracs

Aim: This activity is used to demonstrate how reflection occurs using a mirror and an OHP.

Equipment: The equipment includes...  

• Overhead projector;
• Overhead projector screen;
• 2 pieces of paper;
• mirror.

Method: Place 2 pieces of paper on an overhead projector so that a thin vertical beam of light is displayed on the OHP screen. Ask the question "Would it be brighter placing a mirror into the path of the bright light?"

Background knowledge: The mirror ends up being much less bright unless it reflects directly into your eyes. All objects reflect light to some extent. If you look very closely at the surface of an object, the smoother the surface, the more likely you can see your reflection (eg. the surface of glass is extremely smooth, compared to the surface of an overhead projector screen).

What is a mirror made of? A mirror is a piece of glass with a film of reflective material glued to the back of it. The glass itself is used to support the very thin film of reflective material. If you scratch it off, you can "see" through the mirror.

Smooth Vs rough surface: A cupboard can be bought with no varnish. It looks "rough" and no reflection can be seen in the surface. Once the cupboard is varnished is "shines". The surface has become much smoother (therefore reflecting light much more regularly).