(a) Draw ray diag

(a)

i.

ii.

(b)SINCE image is formed on other side of the lens the lens used is a convex lens. The magnification for a convex lens is negative.

M = -3; v = + 80 cm; u = ?

m = v/u

So u = v/m

= 80/(-3)

u = 26.6 cm

The nature of image is real, inverted, enlarged.

OR

Laws of refraction of light:

a. The incident ray, the normal to the refracting surface at the point of incidence and the refracted ray all lie in one plane.

b. For the light of a given colour and for a given pair of media, the ratio of sine of angle of incidence i to the sine of angle of refraction r is a constant.

sin i/ sin r = constant

ABCD is a rectangular glass slab. As shown in figure light ray is incident obliquely at an angle of incidence i. Since light rays travel from air to glass i.e. rarer to denser medium, the light ray bends towards the normal NN’. The refracted ray is then incident on opposite surface CD. Then light travels from glass to air i.e. denser to rarer medium, it bends away from normal MM’. The emergent ray is parallel to the incident ray.