Define the power of lens.

The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. We can also define the power of the lens as the reciprocal of its focal length in metres. Power = 1 Focal length of the lens ( in metres ) P = 1 f For a concave lens, the focal length is negative and so power is negative. For the convex lens, the focal length is positive and so, the power is positive.

Define the term magnification of a spherical lens.

The size of the image with respect to the object is given by linear magnification. Thus, we can define linear magnification as the ratio of the height of the image h 2 to the height of the object h 1 . Magnification = Height of image Height of object m = h 2 h 1 The linear magnification ( m ) of a spherical lens can also be related to the object distance ( u ) and the image distance ( v ) , then Magnification = Image distance Object distance m = v u For the concave lens, magnification is positive and for the convex lens, when the image is virtual, magnification is positive and when the image is real, the magnification is negative.

Define the focal length of a spherical mirror.

A spherical mirror is a mirror whose reflecting surface is a part of a hollow sphere of glass. There are two types of spherical mirrors namely, concave mirror and convex mirror. The focal length of a spherical mirror is the distance between the pole P and the principal focus F of the mirror. The focal length of a spherical mirror is denoted by the letter f . If R is the radius of the curvature and f is the focal length of the spherical mirror (convex or concave), then f = R 2

Write any three uses of concave mirror.

The spherical mirror in which the reflection of light takes place at a bent surface (concave surface) is called a concave mirror. The following are the three uses of a concave mirror: 1) A concave mirror is used as a make-up and shaving mirror as it can form an erect and magnified image of the face When the face is held within the focus of a concave mirror, then an enlarged image of the face is seen in the concave mirror 2) A concave mirror is used as a reflector in torches, headlights of motor vehicles etc., to get a powerful parallel beam of light 3) The concave mirrors are used to concentrate sunlight to produce heat in solar devices

Draw a ray diagram of refraction of light through a rectangular glass slab.

The change in the direction of light when it passes from one medium to another is known as the refraction of light. The following diagram represents the refraction of light through a rectangular glass slab. On entering into the glass medium from the air, the light ray bends towards the normal. That means the light ray gets refracted on entering the glass medium. After the refraction, this ray now travels through the glass slab. Then it comes out of the glass slab by refraction from the other interface boundary. When the ray goes from glass medium to air it again gets refracted and bends away from normal. Here, the incident ray and the emergent ray are parallel to each other. Here, i ( i 1 & i 2 ) is the angle of incidence, r is the angle of refraction and e is the angle of emergence. Since emergent ray and incident ray are parallel to each other, the angle of incidence and angle of emergence are equal. The perpendicular distance between the original path of the incident ray and the emergent ray coming out of a glass slab is known as lateral displacement.