  The slope and curvature of Isgur Wise function for $B_{c}$ meson is computed
in a QCD potential model in two different approaches of choosing the
perturbative term of the Cornell potential. Based on heavy quark effective
theory the exclusive semileptonic decay rates of $B_c$ meson into the $c\bar c\
(\eta_c,J/\psi)$ states are exploited. Spin symmetry breaking effects are
ignored upto a particular point and the form factors are connected with
Isgur-Wise function for other kinematic point since the recoil momentum of
$c\bar c$ from $B_{c}$ is small due to its heavy mass.
