A rectangular coil with resistance 200ohms has 50 turns each of length l=10cm an
ID: 2244498 • Letter: A
Question
A rectangular coil with resistance 200ohms has 50 turns each of length l=10cm and width w=5cm. the coil moves into a uniform magnatic feild B=1.2T with constant velocity V=10m/s.
In all cases calculate the magnitude And the direction
a) Calculate the induced emf when the right edge is about to penetrate the feild.
b) Calculate the induced emf when the left edge of the coil is about to penetrate the feild.
c) Calculate the induced emf when the left edge of the ccoil moves from beig just totally inside the feild (on the left side) until it is just about to emerge from the feild on the right.
d)Calculate the force on each of the edges of the coil.
i)While the coil is penetrating the feild and ii) while it is totally inside the feild.
e) Now the coil is lying motionless and flat within the feild and it is rotated about an axes through the right side of the coil, such that the left side rises, leaving the coil prependicular to the feild. this is done in 0.1 seconds. what is the average emf induced in the coil and what is the average induced current.
Explanation / Answer
a) EMF = N*BVW = 50*1.2*10*0.05 = 30V (only in right vertical arm)
b) EMF = N*BVW = 50*1.2*10*0.05 = 30V (only in right vertical arm)
c) EMF is induced in both the vertical arm with same sign(+ve end up)
Net EMF = 0.
d) i) While penetrating, I = EMF/R = 0.15 A (current is anti clockwise)
F = N*BI* length = 9*length
right vertical arm = 9*0.05 = 0.45 N (towards left)
Top horizontal arm = 9*0.1 = 0.9 (down)
Bottom horizontal arm = 9*0.1 = 0.9 (up)
{ Note : Net force will be only due to right arm.}
ii) When totally inside, EMF = 0. Current = 0. So, net force = 0. (also Force is 0 individually on each arm)
e) Average angular velocity,w = pi/(2*t) = 15.7 rad/s
Induced current is due to change in flux.
Flux, B = B.A = BA cos(angle) ; angle a = wt
EMF = -dB/dt = (BAw)* sin(wt)
Average of sin in one fourth cycle is (2/pi)
EMF = 0.06 V
I = 0.06/200 = 0.3 mA
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