IEMDaily - Video Lecture Notes

Definition

Magnification of mirrors

Magnification is the increase in the image size produced by spherical mirrors with respect to the object size. It is the ratio of the height of the image to the height of the object and is denoted as m. The magnification, m produced by a spherical mirror can be expressed as:

m = \frac{h}{h}

Here, h is the height of image and h is the height of the object.

Magnification is also equal to the ratio of image distance to the object distance.

m = \frac{v}{u}

As the object is always above the principal axis, the height of the object is always positive. But sign for image height may vary according to the type of image formed. The height of virtual images should be taken positive while the height of real images should be taken negative.

Example

Uses of spherical mirrors

Spherical mirrors has various applications. Some applications of convex mirror are sunglasses, rear view mirrors, shaving mirror,etc. Some applications of concave mirrors are reflectors, converging of light, solar cooker etc.

Definition

Convex mirror as Side View Mirror

Uses of Convex mirror:

It is used as a side view mirror in vehicles in order to obtain the real image of vehicles coming behind for safe driving.Convex mirror reflect the light outward,its a diverging mirror hence can be used in focusing of light.
It is used as the reflectors in street lamp.
It is often used as the surveillance mirror.
It is used in making of optical instruments like telescope.

Definition

Erect and inverted image

An erect image, in optics, is one that appears right-side up. It is an image in which directions are the same as those in the object, in contrast to an inverted image.

Definition

Terms related to spherical mirrors

Centre of curvature (C): Centre of the sphere of which the mirror is a part.
Radius of curvature (R): Radius of the sphere of which the mirror is a part.
Pole (P/O): Geometric centre of the spherical surface of the mirror.
Principal axis: Straight line joining the pole of the mirror to its centre of curvature.

Definition

Focus, Focal length and focal plane of spherical mirrors

The plane through the focus perpendicular to the axis of a mirror or lens is called focal plane.

Definition

Define focus, focal length and focal plane of spherical mirrors

Focus
Definition: For a concave mirror. The rays traveling parallel to the principal axis of a mirror after reflection pass through (converge at) a point F This point F is known as the principal focus of the concave mirror. It is a real point in front of a mirror.
For a convex mirror. The rays traveling parallel to the principal axis of a mirror after reflection appear to diverge from a point F on the principal axis. This point F is known as the principal focus of the convex mirror. It is a virtual point, i.e., behind the mirror.
Focal length
Definition:The focal length (f) is the distance between the lens and the focal point.

Focal Plane:
Definition:
A vertical plane passing through the principal focus and which is perpendicular to the principal axis is called focal plane.

Definition

Principal focus and focal plane

A principal focus or focal point is a special focus:

For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points one on each side.
Elliptical mirrors have two focal points: light that passes through one of these before striking the mirror is reflected such that it passes through the other.
The focus of a hyperbolic mirror is either of two points which have the property that light from one is reflected as if it came from the other.

The plane perpendicular to the axis of a mirror containing the principal focus is called the focal plane.