Consider a laminar boundary layer over a heated flat plate. The free stream velocity is $U_{\infty }.$ At some distance x from the leading edge the velocity boundary layer thickness is $\delta _{v}$ and the thermal boundary layer is $\delta _{r}$. if the Prandtl number is greater than 1, then (GATE-ME-2003)
(a) $\delta _{v}> \delta _{r}$ (b) $\delta _{r}> \delta _{v}$
(c) $\delta _{v}=\delta \sim \left ( U_{\infty } \right )$ (d) $\delta _{v}=\delta _{r}\sim x^{-1/2}$