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A semicircular loop of radius *R* is rotated with an angular velocity ω perpendicular to the plane of a magnetic field *B* as shown in the figure. Emf induced in the loop is

(1)

*BωR*

^{2}(2) $\frac{1}{2}B\omega {R}^{2}$ (3) $\frac{3}{2}B\omega {R}^{2}$ (4) $\frac{1}{4}B\omega {R}^{2}$