Rainbow — Prelims Strategy

Prelims Strategy

To effectively tackle NEET questions on rainbows, a multi-pronged strategy is essential. Firstly, master the fundamental concepts: clearly understand dispersion, refraction, and total internal reflection.

Know Snell's law ($n_1 sin \theta_1 = n_2 sin \theta_2$) and the critical angle formula ($sin \theta_c = \frac{n_{\text{rarer}}}{n_{\text{denser}}}$). Secondly, memorize the key characteristics of primary and secondary rainbows: this includes the number of internal reflections (1 for primary, 2 for secondary), their relative brightness (primary brighter), the order of colors (ROYGBIV for primary, VIBGYOR for secondary from top to bottom), and their approximate angular radii ($42^circ$ for primary, $51^circ$ for secondary).

Thirdly, understand the observation conditions: the sun must always be behind the observer, and the rainbow appears opposite the sun (at the anti-solar point). For numerical problems, carefully identify the given refractive indices and angles.

For conceptual questions, visualize the light path and apply the principles step-by-step. Be wary of trap options that mix up the properties of primary and secondary rainbows or incorrectly attribute phenomena like diffraction to the main rainbow formation.

Practice drawing simple ray diagrams to reinforce understanding.