question_answer 49)

  Between the primary and secondary rainbows, there is a dark band known as Alexandra?s dark band. This is because (a) light scattered into this region interferes destructively. (b) there is no light scattered into this region. (c) light is absorbed in this region. (d) angle made at the eye by the scattered rays with respect to the incident light of the sun lies between approximately 42° and 50°.

Answer:

    (a,d) Alexandar's dark band between the primary and secondary rainbows is because light scattered into this region interferes destructively. Further, primary rainbow subtends an angle of 41°-43° at the eye of the Observer w.r.t. the incident light, and secondary rainbow subtends an angle of about 51° to 54° at the eye of the observer w.r.t. the incident light. Therefore, the region between the angles of 41° to 51° is dark. Choices (a) and (d) are correct