  We study the slope $\rho^{2}$ and curvature $C$ of Isgur Wise function for
the heavy-light mesons in general with particular emphasis on $B$ meson in a
QCD Potential model. The IW function is then used to compute the partial decay
width and branching ratio for the semileptonic decay of
$\left(B^{0}\rightarrow{D,D^{*}l\nu}\right)$. The computed value of the CKM
element $|V_{cb}|=0.040$ is found to be in agreement with the available data.
