Light

Light is a form of energy that travels away from the source that produces it at a speed of 3×10⁸ m s^-1

Crooke’s Radiometer

• Converts light energy into kinetic energy.
  - shows that light is a form of energy

Light usually travels in straight lines

Reflection of Light

• The bouncing of light from the surface of an object.

• There are two types of reflection, diffuse and regular.

Diffuse Reflection

• When light strikes a matt surface (non smooth surface) the reflected light is scattered in all directions.

• Most everyday objects are visible by light which has been diffusely reflected from them.

Regular Reflection

• If the surface that the light strikes is silvered and polished smooth (e.g. a mirror) the light is not scattered and reflected directly.

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.

Optics

There are two types of images:
- real images
- virtual images

Virtual Image:
An image formed by the apparent intersection of rays.
A virtual image cannot be formed on a screen.

Image in Plane Mirror:
A virtual/upright/the same distance behind the mirror as the object is infront of the mirror.
Objects are flipped (lateral inversion) e.g. ambulance in rear view mirror

The apparent movement of one object relative to another due to the motion of the observer is called parallax. The object that is farthest away appears to move with the observer.

Reflection of Light from Spherical Mirrors

Concave and Convex Mirrors

• The reflecting surface of a concave mirror caves in at the centre.

• The reflecting surface of a convex mirror bulges out at the centre.

Describing Concave and Convex Mirrors

1. When a ray strikes the pole of a concave
mirror it is reflected at an equal angle with the axis.

2. When a ray passes through the centre of curvature
of a concave mirror it is reflected back along its on path.

3. When a ray comes parallel to the axis and strikes
a concave mirror it passes through the focus after reflection.

4. When a ray passes through the focus and strikes
a concave mirror it is relfected out parallel to the axis.

Real Image

• An image formed by the actual intersection of rays.

• A real image can be formed on a screen.

u = object distance to mirror

v = image distance to the mirror

f = focal length

Uses of a Concave Mirror

• Dentist’s Mirror

• Floodlights

• Projector

• Torch

• Solar Furnace

• Cosmetics Mirror

Formulae for Concave Mirrors

Qualities of Images Formed by a Concave Mirror

Outside Focus:
Image = Real, Magnified, Upside Down

On Focus:
Image = Formed at infinity

Inside Focus:
Image = Virtual, Magnified, Upright

Outside Centre of Curvature:
Image = Real, Diminshed, Upside Down

Convex Mirrors

In a convex mirror, the image is always virtual.

Rules for Convex Mirrors

Rule 1
Ray that strikes the pole is reflected at an equal angle with the axis.

Rule 2
Ray that is heading for the centre of curvature is reflected along back its own path.

Rule 3
If a ray is parallel to the axis then it reflects as if it came from the focus behind the mirror.

Rule 4
A ray that is heading for the focus and strikes the mirror is reflected out parallel to the axis.