CBSE Class 12-science Answered

(a) QR is horizontal

(b) chromatic aberration

(c) real and inverted

(d)

Rainbow is a phenomenon arising due to combined effect of dispersion, refraction and reflection of sunlight by spherical water droplets of rain. An observer can see a rainbow only when his back is towards the sun. Sunlight is first refracted as it enters a raindrop, which causes the different wavelengths of white light to separate. Longer wavelength of light (red) are bent the least while the shorter wavelength (violet) are bent the most. Next, these component rays strikes the inner surface of the water drop and get internally reflected if the angle between the refracted ray and normal to the drop surface is greater than the critical angle. The reflected light is refracted again as it comes out of the drop. It is found that the violet light emerges at an angle of 40º related to the incoming sunlight and red light emerges at an angle of 42º. For other colours, angles lie in between these two values.