Where there is a magnetic field pointing into the page, (magnetic field indicate

Question

Where there is a magnetic field pointing into the page, (magnetic field indicated by the shaded region). When the loop of wire is in the position shown in the figure, is there an induced cur-rent in the loop? The current runs counterclockwise Unable to determine No the current runs clockwise. A maximum emf of 98.0 V is induced in a generator coil rotating with a frequency of 52 Hz. The coil has an area of 210 cm2 and rotates in a magnetic field of 3.1 T. How many whole number of turns are in the coil? Answer in units of turns. A pendulum consists of a supporting rod and a metal plate (see figure). The rod is pivoted at O. The metal plate swings through a region of magnetic field (directed out of the paper). Consider the case where the pendulum's metallic plate enters the magnetic field region from left to right. The direction of the induced magnetic field at the center of the circulating eddy current and the direction of the eddy current are along the rod away from the pivot point and counter-clockwise. Into the plane and counter-clock wise. opposite to the direction of swing and counter-clock wise. along the direction of swing and clockwise. Out of the plane and counter-clock wise. Opposite to the direction of swing and clockwise. Along the direction of swing and counter clock wise. Along the rod toward the pivot point and clockwise. Into the plane and clock wise. Out of the plane and clockwise.

Explanation / Answer

Ans 005 - As the loop is moving with a velocity v inside the magnetic field B, voltage will induce in this loop in the direction opposite to the direction of (v x B) according to the Lenz's law-

so the current will flow in the Clockwise direction as the direction of (v x B) is in the counter-clockwise direction according to the right-hand rule.

Ans 006-

Faraday law of induction:

emf = N /t

induced emf is directly proportional to the number of coil turns, and the time rate of change of magnetic flux, defined as the scalar product of field density B and area A.

B =3.1 T; A can be regarded as a variable (a function of time). Magnetic flux varies as coil rotates, so the product = B·A is actually BA cos , where is the angle between vector B and the vector normal to area A. varies as a function of time according to = t, where = 2f. Since f is specified as 52.0 Hz, = 2 x 52 = 104. Therefore,

emf = N (B·A)/t = NB (A cos t)/t, where A = 210 Cm².

Now, since d (cos t)/dt = sin t,

emf = NBA sin t.

Maximum value for emf occurs when sin t = 1, so

emf (peak) = NBA

N = emf (peak)/BA = 98.0 / (3.1 × 210 x 10-4 x 104 ) =4.6 turns.

N = 5 turns (approx.)

Ans 007-

Conduction electron will experience a magnetic force opposite to (v x B), we can determine the motion of the electrons in the counter-clockwise direction so the current will flow in the clockwise direction.

As the magnetic field is pointing out of the paper, the magnetic flux through the pendulum is increasing. Thus by Lenz's law, induced emf will be in opposite direction i.e. into the plane.

answer -9

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