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# A metal disc of diameter 20cm makes 1200rpm about its axis kept parallel to a uniform magnetic field of induction 10^-2T. The emf induced between the the centre and the rim of the disc is?

PRASHANT KUMAR
8 Points
2 years ago
Zero. Because flux is B.ds and here angle is 90 degree so its zero and emf is rate of change of flux so zero.
ketaka singh
10 Points
2 years ago
Frequency of rotation = 20 cycles per sec implies $\omega = 2\pi f = 40 \pi rad/sec$
Consider a point A on the circumference if the disc.
Now consider a small element of length dx at a distance x from the centre if the disc on the line joining A and the centre.

Emf induced in this length dx , de = B(dx)v = B$\omega$xdx
Net emf induced between the centre and point A is

E = $\int de$=$\int_{x=0}^{x=r}B\omega xdx= B\omega r^{2}\frac{1}{2}$

Calculating we get E = 6.28 × 10^-3