This set of Electromagnetic Theory MCQs focuses on “Magnetic Torque”.
1. Find the force that exists in an electromagnetic wave.
a) Electrostatic force
b) Magnetostatic force
c) Lorentz force
d) Electromotive force
Explanation: In an electromagnetic wave, the force of the electric and magnetic field both coexist. This is given by F = qE + q(v x B). It is called Lorentz force.
2. In an field having a force of 12N and distance 20cm, the torque will be
Explanation: The torque is defined as the product of the force and distance in a field. Thus T = F x d = 12 x 0.2 = 2.4 units.
3. Find the torque in a conductor having current 2A, flux density 50 units, length 15cm and distance of 8m.
Explanation: The torque on a conductor is given by T = BILd, where L x d is the area of the conductor. Thus the torque will be, T = 50 x 2 x 0.15 x 8 = 120 units.
4. The distance of the conductor when the area and length of the conductor is 24m2 and 13.56m.
Explanation: We know that the surface integral is the area component which is the product of two dimensions given by length and distance in a conductor. Thus A = L x d. To get d, d = A/L = 24/13.56 = 1.76 units.
5. The torque on a conductor with flux density 23 units, current 1.6A and area 6.75 units will be
Explanation: The maximum torque on a conductor will be at perpendicular angle ie, at 90. The torque will be given as T = BIA, where B = 23, I = 1.6 and A = 6.75.Thus we get, T = 23 x 1.6 x 6.75 = 248.4 units.
6. Consider the conductor to be a coil of turns 60 and the flux density to be 13.5 units, current 0.12A and area 16units. The torque will be
Explanation: For a single turn or loop, the torque will be BIA. For N turns, the torque will be T = NBIA, where N = 60, B = 13.5, I = 0.12 and A = 16. Thus T = 60 x 13.5 x 0.12 x 16 = 1555.2 units.
7. The torque of a conductor is defined only in the case when
a) The field is perpendicular to the loop
b) The plane of the loop is parallel to the field
c) The plane of the loop is perpendicular to the current direction
d) The field and the current direction are same
Explanation: The torque of a conductor is given by T = NBIA. This equation of the conductor is valid only when the plane of the loop is parallel to the magnetic field applied to it.
8. Find the angle at which the torque is minimum.
Explanation: The torque of a conductor loop is given by T = BIA cos θ. The torque is minimum refers to zero torque. This is possible only when the angle is 90 or perpendicular.
9. The magnetic moment and torque are related as follows
a) T = BM
b) B = TM
c) M = TB
d) T = M
Explanation: The torque is defined as the product of the magnetic flux density and the magnetic moment. It is given by T = BM, where M = IA is the magnetic moment.
10. Calculate the magnetic moment when a field of B= 51 units is subjected to a torque of 20 units.
Explanation: The magnetic moment is given by the ratio of the torque and the magnetic flux density. Thus M = T/B, where T = 20 and B = 51 units. We get M = 20/51 = 0.39 units.
Sanfoundry Global Education & Learning Series – Electromagnetic Theory.
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