Chapter 2 Geometrical Optics

What is Light? Light is a Form of Energy that travels away from the source producing it at a Speed of 300 000 000 m s-1.

Converting Light Energy to Electrical Energy

Crooke’s Radiometer converts Light Energy into Kinetic Energy.

Light usually travels in straight lines

Reflection of Light The bouncing of light from the surface of an object is called Reflection.

There are two kinds of reflection: Diffuse Reflection Regular Reflection

Diffuse Reflection When light strikes a matt surface (non smooth surface), the reflected light is scattered in all directions. This is Diffuse Reflection. Most everyday objects are visible to you by light which has been diffusely reflected from them.

Regular Reflection If the surface that the light strikes is silvered and polished smooth, i.e. if it is a mirror, the light is reflected as shown. This is called Regular Reflection.

Terms used to describe Regular Reflection

State The Laws of Reflection of Light Law 1: The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane. Law 2: The angle of incidence is equal to the angle of reflection. i = r .

The Incident Ray, the Normal at the point of incidence and the Reflected Ray all lie in the Same Plane.

Angle of Incidence = Angle of Reflection. i = r

How an Image is formed in a plane mirror

What is a Virtual Image? A Virtual Image is an image formed by the Apparent Intersection of Rays. A virtual image cannot be formed on a screen.

An image in a plane mirror is: Virtual Upright The same distance behind the mirror as the object is in front of the mirror

The Periscope

The image of a right hand in a plane mirror is a left hand The image of a right hand in a plane mirror is a left hand. This is called Lateral Inversion.

The front of an ambulance has “ ” written on it. A driver ahead will see “AMBULANCE” in the rear view mirror . AMBULANCE

To demonstrate the Laws of Reflection (i) Set up the equipment as shown. With a pencil, mark the position of the ray before and after it strikes the mirror. Mark the position of the mirror. Remove the mirror and draw in the normal at the point of incidence. With a protractor measure the angle of incidence (i) and the angle of reflection (r). Repeat the experiment for different values of i. It will be found that the Angle of Incidence is equal to the Angle of Reflection. Sheet of Paper

To demonstrate the Laws of Reflection (ii) It is also found that the reflected ray will be travelling parallel to the paper, i.e. it will not be heading up from the paper or heading into the paper. It will be in the same plane as the incident ray and the normal thus showing the First Law. Sheet of Paper