Activity 9.10

Activity . Fix a sheet of white paper on a drawing board using drawing pins. Place a rectangular glass slab over the sheet in the middle. Draw the outline of the slab with a pencil. Let us name the outline as ABCD. Take four identical pins. Fix two pins, say E and F, vertically such that the line joining the pins is inclined to the edge AB. Look for the images of the pins E and F through the opposite edge. Fix two other pins, say G and H, such that these pins and the images of E and F lie on a straight line. Remove the pins and the slab. Join the positions of tip of the pins E and F and produce the line up to AB. Let EF meet AB at O. Similarly, join the positions of tip of the pins G and H and produce it up to the edge CD. Let HG meet CD at O ′ . Join O and O ′ . Also produce EF up to P, as shown by a dotted line in Fig. . . Figure . Figure . Figure . Figure . Figure . Refraction of light through a rectangular glass slab The following are the laws of refraction of light. (i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. (ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction. (This is true for angle < i < o ) If i is the angle of incidence and r is the angle of refraction, then, sin sin i r = constant ( . ) This constant value is called the refractive index of the second medium with respect to the first. Let us study about refractive index in some detail.