The primary colours of light are MCQ with Answer and Explanation

Explanation:
R ∝ L² (volume constant). L'=3L => R' = 3² × 6 = 9×6 = 54 Ω. Generally, R' = n² R for stretching n times. Important concept.

Explanation:
For a bipolar junction transistor (BJT) in common-emitter configuration, DC current gain β = I_C / I_B, where I_C is collector current, I_B base current. Typical β values range 20-200. Option D is α (common-base gain). Memory tip: 'β = collector current / base current; large β means small base current controls large collector current'. This definition-based question tests electronics fundamentals, frequently examined in competitive exams. Always distinguish β (CE configuration) from α (CB configuration) and their relationship: β = α/(1-α).

Explanation:
Rayleigh scattering of sunlight by air molecules, blue scattered most.