Please remember that \'rpm\' (rev/min) is NOT an SI unit. You will need to conve

Question

Please remember that 'rpm' (rev/min) is NOT an SI unit. You will need to convert to rad/s. Recall 1 rev=2 radians.

A generator is designed to produce a maximum emf of 130 V while rotating with an angular speed of 3600 rpm. Each coil of the generator has an area of 0.061 m2. If the magnetic field used in the generator has a magnitude of 0.050 T, how many turns of wire are needed?
____________ Turns

During the rotation of the coils, the magnetic flux through the coils will alternately be increasing and decreasing. (Why?)

While the flux is increasing, the induced current in the coils will make a B field which tries to the external B field. (oppose, reinforce, neither, not enough info)

While the flux is decreasing, the induced current in the coils will make a B field which tries to the external B field. (oppose, reinforce, neither, not enough info)

This generator will produce what kind of current? (DC, AC, Neither, Not Enough Info)

Explanation / Answer

Maximum emf E = 130 V

Angular speed w = 3600 rpm

                           = 3600 * 2(pi) rad / 60 s

                           = 376.99 rad / s

Area   A= 6.1 * 10^-2 m ^ 2

Magnetic field B = 5 * 10 ^ -2 T

We know E = BANw

From this No.of truns N = E / ( BA w )

                                        = 113.06

flux = B*A*cos(theta) , where theta is the angle between B and A.

-1 <= sin(theta) <=1

Hence, magnteic flux will increasing and decreasing over time ..

While the flux is increasing, the induced current in the coils will make a B field which tries to oppose.

While the flux is decreasing, the induced current in the coils will make a B field which tries to reinforce.

Generator will produce Alternative current (AC).

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