38.5 sq cm

Because it occurs after the rain when there are still some of the suspended water droplets present in the atmosphere . These water droplets acts as a prism and the light rays from the sun acts as the incident ray , and the light is refracted as well as dispersed. So, the rainbow...........

A shape factor is used in boundary layer flow to determine the nature of the flow. H= frac {delta^*}{theta} where H is the shape factor, δ * is the displacement thickness and θ is the momentum thickness. Displacement thickness is defined as the distance that the surface would have to displace outwards in an inviscid flow in order to give the same mass flow rate deficit as that which exists in the boundary layer. Momentum thickness is defined as the distance that the wall would have to displace outwards in an inviscid flow in order to give the same momentum deficit (per unit width) of the mass flow rate. The higher the value of H, the stronger the adverse pressure gradient. Large values of H implies that boundary layer separation is about to occur.

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