1) A wire loop of radius 0.40 m lies so that an external magnetic field of magni
ID: 1321363 • Letter: 1
Question
1) A wire loop of radius 0.40 m lies so that an external magnetic field of magnitude 0.30 T is perpendicular to the loop. The field reverses its direction, and its magnitude changes to 0.20 T in 1.5 s. Find the magnitude of the average induced emf in the loop during this time.
2) In a model AC generator, a 499 turn rectangular coil 6.0 cm by 22 cm rotates at 116 rev/min in a uniform magnetic field of 0.55 T.
(a) What is the maximum emf induced in the coil?
(b) What is the instantaneous value of the emf in the coil at t = (?/40) s? Assume that the emf is zero at t = 0
(c) What is the smallest value of t for which the emf will have its maximum value?
Explanation / Answer
1.) It is important to realize that the field is not only changing in magnitude but also changing directions.
The magnetic field changes magnitude AND reverses directions.
So if your initial field direction was positive, then your final field direction is negative. The same goes for your flux (initially the flux was +, then it changes to -).
2.)
Hello recall the induced emf e = N B A w sin wt
N - number of turns
B - magnetic field induction 0.6 T
A - 260 cm^2 = 2.6 * 10^-2 m^2
w - angular frequency 2 pi*116 rad/min ie 2*3.14*116/60 rad/s ie Hz
N B A w is the max induced emf.
Plugging the values and we get, 94.5 V
So max emf = 94.5 V
HEnce e = 94.5 sin (2*pi*116/60 t)
Plugging t = pi/33, we get e = 1.91 V
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