1. A circular plate of radius 0.5 m is placed perpendicular to the direction of

Question

1. A circular plate of radius 0.5 m is placed perpendicular to the direction of the magnetic field of 0.5 Tesla. What is the change of flux in the plate if it rotates and its plane becomes parallel to the direction of the magnetic field?

2. A 0.35 m2 coil with 50 turns rotates at 5 radians per sec2 in a magnetic field of 0.6 Tesla. What is the value of the rms current in the coil if the coil has the resistance of 3.3 Ω

3. A step-up transformer used in a car has a potential difference of 10 V across the primary coil with 12 turns. What is the current in the secondary coil of resistance 2.5 Ω if the number of turns in the secondary coil is 54 turns?

4.

Explanation / Answer

1. A= pi*R^2 = pi*.25 = 0.785 m^2
Flux = B*A = 0.5T*0.785m^2 = 0.39 weber. This is the change in flux.

2. V=IR, and V is from Faraday's Law; V = (-)N * ∆flux/∆time
rate of change of flux is -BA(omega)sin(omega*t)
Don't forget V(rms) = V(peak)/root 2

3. V1/n1=V2/n2, and V=IR

4. Force F on wire of length L carrying current i is i*LxB where F, L and B are vector quantities. "x" means "vector cross-product". The magnitude of the cross-product of two vectors is the product of their magnitudes times the sine of the angle between them. Thus, To get zero force on the wire, B must be in the same direction as the wire. Any other B direction will apply a force to the wire per the above formula,i.e in a direction perpendicularto L and B..

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