$\begin{aligned} & \mathrm{B}_{\mathrm{H}}=4 \times 10^{-3} \mathrm{~T} \\ & \theta \rightarrow 45^{\circ} \\ & \mathrm{B}_{\mathrm{v}}=\mathrm{B}_{\mathrm{H}} \\ & \epsilon=(\overrightarrow{\mathrm{V}} \times \overrightarrow{\mathrm{B}}) \cdot \vec{\ell} \\ & =\left(\left(4 \times 10^{-3}\right)(20)\right) \frac{20}{100} \\ & =16 \times 10^{-3} \mathrm{~V}=16 \mathrm{mV}\end{aligned}$