A student traces the path of a ray of light passing through a rectangular slab for three different values of angle of incidence (Zi) namely 30, 45 and 60. He extends the direction of incident ray by a dotted line and measures the perpendicular distance 'l' between the extended incident ray and the emergent ray. He will observe that (a) 'I' keeps on increasing with increase in angle of incidence (b) 'I' keeps on decreasing with increase in angle of incidence (c) 'I' remains the same for all three angles of incidence (d) 'l' is the maximum for Zi = 45 and is less than this value for Zi = 30 and Zi = 60.