What do you understand by the term refraction of light?

The phenomenon in which the rays travelling from one transparent medium to another transparent medium change their path at the surface of separation of the two given media is called refraction of light. It appears when light travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light. Note: No refraction of light takes place, if a beam of light strikes another optical medium at right angles.

State two characteristics of image formed in a plane mirror.

The image formed by a plane mirror is:- i. The image formed by a plane mirror is virtual and erect, ii. Same size as of the object and same distance from the mirror as the object, iii. Laterally inverted.

Give any four characteristics when the object is at the centre of curvature of a concave mirror.

When an object is placed at the centre of curvature in front of a concave mirror the following characteristics can be observed from the figure. The image will also be located at the centre of curvature. The image will be inverted. The size of the image will be equal to the size of the object. The formed image will be real and inverted.

A convex lens of focal length 40 cm and a concave lens of focal length 50 cm are placed in contact with each other. Calculate (i) the power of the Combination and (ii) the focal length of the combination.

Given: The focal length of the convex lens, f 1 = + 40 cm = + 0 . 4 m The focal length of the concave lens, f 2 = - 50 cm = - 0 . 5 m We have the power of the lens, P = 1 f Therefore, the power of the convex lens, P 1 = 1 f 1 = 1 0 . 4 = 2 . 5 D Similarly, the power of the concave lens, P 2 = 1 f 2 = 1 - 0 . 5 = - 2 D The resultant or net power of combination, P = P 1 + P 2 = ( 2 . 5 D ) + - 2 D = 0 . 5 D The focal length of the combination of lenses, f = 1 P = 1 0 . 5 = 2 m . Since the total power is positive, the combination will act as a convex lens.

An eye specialist prescribes a power + 4 . 5 D to a person for his glasses. What are the nature of the lens and the focal length of the lens?

A lens having a power + 4 . 5 D . The relation between the power and the focal length of a lens is given by P = 1 f + 4 . 5 D = 1 f f = 1 4 . 5 = 2 9 = 0 . 22 m The focal length is + 0 . 22 m . The nature of the lens is converging type or convex lens. The defect of the eye is Hyperopia or far-sightedness.