Question

23. Which of the following phenomena is/are associated with Rainbows?
1. Refraction 2. Total Internal Reflection
3. Dispersion
Select the correct answer using the codes given below.

• A. Only 1 and 2
• B. Only 1
• C. Only 1 and 3
• D. All of the above

Answer 1

The correct option is D All of the above

1. The light that is not refracted crosses the air-water interface (boundary layer). When this happens it slows down because the water is denser than the air. The reduction of speed causes the path of the light to bend - this is called refraction. In this case the path of the light rays bends toward the normal line.
2. White light is made up of a spectrum of colours, each with its own wavelength. Different wavelengths travel at different speeds and when they encounter a change to medium that is denser or less dense, the speeds are affected by different amounts. Hence, the colours separate. This phenomenon is known as Dispersion.
3. At the rear of the raindrop, the light hits the water-to-air interface. If the angle of incidence is greater than the critical angle, Total Internal Reflection will occur. A rainbow will only be seen if this happens, otherwise the light will continue out the other side of the raindrop and continue to move away from the would-be viewer.