Which of the following statements with regard to the phenomenon of the primary rainbow formation by water droplets is/are correct ? 1. It involves refraction and one internal reflection of sunlight. 2. It involves refraction of sunlight only. 3. It is formed as the inner bow. 4. It may involve more than one internal reflection as well as refraction of sunlight. Select the answer using the code given below :

The correct answer is B, 1 and 3. A primary rainbow comes from light that is refracted into a raindrop, reflected once inside it and refracted out again, and it is the brighter, inner bow.

When sunlight enters a spherical drop it bends and splits into colours (dispersion), reflects once off the back of the drop and bends again as it leaves. The light emerges at about 40–42 degrees from the direction opposite the Sun, so the bow appears with red on the outside and violet on the inside. A secondary rainbow forms when the light reflects twice inside the drop; it is fainter, lies outside the primary bow at about 51 degrees and has its colours reversed.

A is wrong because statement 3 is also correct. C is wrong because statement 4 describes the secondary bow, not the primary one. D is wrong because refraction alone cannot send the light back towards an observer standing with the Sun behind.

Exam tip: primary bow, one internal reflection, inner and brighter, red outside; secondary bow, two reflections, outer and fainter, colours reversed.