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Department of Electronics & Communications,Faculty of Technology,

Dharmsinh Desai University

MCQ for the subjectElectromagnetic Fields

Note: The correct answers for the respective questions are the options given in bold fonts.

(1) Lenzs law is a consequence of the law of conservation of

(a) linear momentum (b) charge (c) angular momentum (d) energy

(2) The electrical entity inductance can be compared to the mechanical entity

(a) energy (b) impulse (c) momentum (d) torque (e) inertia

(3) A jet plane is flying horizontally at a speed of 1800 km/hour. What is the potential

difference developed between the tips of its wings if the wing span is 25m? Earths

magnetic field at the location is 0.4 gauss and the angle of dip is 30.

(a) 25mV (b) 250mV (c) 500mV (d) 2.5V (e) 5V

(4) A circular copper disc 10cm in diameter rotates 1800 times per minute about a central axis

at right angles to the plane of the disc. A uniform magnetic field of 1 tesla is appliedperpendicular to the plane of the disc. The voltage induced between the centre and the edge

of the disc is

(a) 0.235V (b) 0. 47V (c) 2.35V (d)4.7V (e) zero

(5) A varying magnetic flux linking a coil is given by = Xt2. If at time t=3s, the emf induced

is 9V, then the value of X is

(a) 0.66 Wb.s-2 (b) 1.5 Wb.s-2 (c) -0.66 Wb.s-2(d) -1.5 Wb.s-2 (e) -0.33 Wb.s-2

(6) A straight copper rod of length L is rotating (with angular velocity ) about an axis

perpendicular to the rod and passing through a point O on the rod, at a distance L/4 fromone end of the rod. A uniform magnetic field B parallel to the axis of rotation exists in the

entire region where the rod rotates. The potential difference developed between the ends of

the rod is(a) BL2 (b) BL2(c) BL2 (d) BL2 (e) 2BL2

(7) When the number of turns in a coil is made 2.5 times the original number without changingthe area, the self inductance of the coil becomes

(a) 2.5 times (b) 5 times (c) 6.25 times (d) 1.25 times (e) 10 times

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(8) If the axis of rotation is parallel to the plane of the coil and perpendicular to the magnetic

field, what is the phase difference between the magnetic flux linkage and the induced emf

in the coil?(a) (b) zero (c) /4 (d) /2 (e) /

(9) The induced emf in a coil is proportional to(a) magnetic flux through the coil (b) area of the coil (c) rate of change of magnetic flux

through the coil (d) product of magnetic flux and area of the coil.

(10) A short circuited coil is placed in a time varying magnetic field. Electric power is

dissipated due to the current induced in the coil. If the number of turns were to be

quadrupled and the wire radius halved, the electrical power dissipated would be(a) halved (b) same (c) doubled (d) quadrupled