Physics 1 FROM 3

<

Physics 1 FROM 3

Chapter 6 MIRRORS

2) CURVE MIRRORS

There are two types of curve mirrors:

  • Concave mirrors and
  • Convex mirrors.

The concave mirror is also now as the diverging mirror.

The convex mirror is also known as the converging mirror.

A curve is a part of a circle. Therefore the center of gravity of a circle will also be the center of the circle and it is called the center of curvature. The radius of a circle will also be the radius of the curve and it is called the radius of curvature.

  • Principal Axis: The principal axis is the line joining the center of curvature and passing through the pole of the mirror.
  • The Focal Length (F): This is the distance from the principal focus to the pole of the mirror.

F= r2

  • Centre of Gravity (C): This is the geometric centre of the hollow sphere of which the mirror is part.
  • The Principal Focus:
  1. For a converging mirror

This is a point on the principal axis where all rays originally parallel and closer to the principal axis will converge after reflection on the mirror surface.

  1. For a diverging mirror

This is a point on the principal axis where rays parallel to the principal axis will appear to come from.

Rules of Rays Construction

  • A ray parallel to the principal axis is reflected to pass through the principal focus F.
  • A ray passing though the centre of curvature is reflected back along its original path.
  • A ray passing through the principal focus is reflected parallel to the principal axis.

 

Object’s position(S) or

Focal point (F)

Image

S<F

- Virtual

- Upright

-Magnified (larger)

S=F

( Object at focal point)

Reflection rays are parallel and never meet, so no image is formed. In the limit where S approaches F, image distance approaches infinity and the image can be either real or virtual and either upright or inverted depending on whether S approaches F from above or below.

F<S<2F

(Object between focus and centre of curvature)

-Real

-Inverted (vertically)

-Magnified (larger)

S=2F

(Object at center of curvature)

-Real

-Vertically inverted

-Same size as image

-Formed at center of curvature

S<2F

(Object beyond centre of curvature)

-Real

-Vertically reduced

-Diminished

-As the distance of the object increases, the image asymptotically approaches the focal point. In the limit where S approaches infinity, the image size approaches.

 

Uses of Concave Mirrors

Commonly, concave mirror can be used as a reflector and enlargement mirror.

  1. As an Enlargement Mirror

When the object is placed less than the focal length of a concave mirror, a large, and upright and virtual image is formed.

Examples are;

  1. Dental mirror
  2. Make-up mirror
  3. Shaving mirror
  1. As a reflector Mirror

Application of Concave Mirrors

A convex mirror has a wider field of vision than a plane mirror. Therefore, it is used as the side mirror of a car, surveillance mirror in a shop and blind corner mirror at a sharp bend road.

F= r2                        1F= 2r                       1u+ 1v= 1F                      1u+ 1v = 2r

 

par Claude Foumtum
Back Next