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

Real Image
\frac{1}{u}+\frac{1}{v}=\frac{1}{f}

Formula for real images

Virtual Image
\frac{1}{u}-\frac{1}{v}=\frac{1}{f}

Formula for virtual images

Magnification
m=\frac{v}{u}

Formula for magnification

Focal Length from Radius
f=\frac{r}{2}

Formula to find focal length from radius

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.

Formulae for Convex Mirrors

Virtual Image
\frac{1}{u}-\frac{1}{v}=-\frac{1}{f}

Formula for virtual images in a Convex mirror

Magnification
m=\frac{v}{u}

Formula for magnification

Focal Length from Radius
f=\frac{r}{2}

Formula to find focal length from radius

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.