A 20 m long uniform copper wire held horizontally is allowed to fall under the gravity ( g=10 m / s^2 ) through a uniform horizontal magnetic field…

A $\displaystyle 20$ m long uniform copper wire held horizontally is allowed to fall under the gravity ( $\displaystyle g=10 \mathrm{~m} / \mathrm{s}^2$ ) through a uniform horizontal magnetic field of $\displaystyle 0.5$ Gauss perpendicular to the length of the wire. The induced EMF across the wire when it travells a vertical distance of $\displaystyle 200$ m is $\displaystyle \_\_\_\_$ mV.