$Cis$-but$-2$-ene is polar and $trans$-but$-2$-ene is non-polar. Explain.

(N/A) $CH_3CH=CHCH_3$ exhibits $2$ geometrical isomers:
$(i)$ $Cis$-but$-2$-ene
$(ii)$ $Trans$-but$-2$-ene
In $cis$-but$-2$-ene,the two $CH_3$ groups are on the same side of the double bond. The bond dipoles of the $C-CH_3$ bonds do not cancel each other,resulting in a net dipole moment $(\mu = 0.33 \ D)$,making it polar.
In $trans$-but$-2$-ene,the two $CH_3$ groups are on opposite sides of the double bond. The bond dipoles of the $C-CH_3$ bonds are equal in magnitude and opposite in direction,thus cancelling each other out. This results in a net dipole moment of zero $(\mu = 0)$,making it non-polar.