This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Generation of an Alternating EMF”.
1. Which, among the following, is the correct expression for alternating emf generated?
Explanation: The correct expression foe alternating emf generated is e=2Blusin(theta). Where, B stands for magnetic field density, l is the length of each of the parallel sides u is the velocity with which the conductor is moved and theta is the angle between the velocity and the length.
2. What should theta be in order to get maximum emf?
Explanation: The value of theta should be 90 in order to get maximum emf because e=2Blusin(theta) and sin is maximum when theta is 90.
3. Calculate the maximum emf when the velocity is 10m/s, the length is 3m and the magnetic field density is 5T.
Explanation: We know that: e=2Blusin(theta)
Substituting the values from the given question, we get e=300V.
4. When a coil is rotated in a magnetic field, the emf induced in it?
a) Is maximum
b) Is minimum
c) Continuously varies
d) Remains constant
Explanation: When a coil is rotated in a magnetic field the emf continuously varies as the cross sectional area varies due to which the number of flux lines crossing it varies, which causes the emf to vary.
5. An E.M.F. can be induced by ___________
a) Change in magnetic field
b) Change in the area of cross section
c) Change in angle between magnetic field and area
d) Change in magnetic field, area and angle
Explanation: This is the dot product of magnetic field vector and area vector.
emf=BAcos(theta), hence if either of the three, that is, magnetic field, area or angle changes, thee emf will change.
6. What is emf?
Explanation: Electromotive force is not actually a force. It is basically a voltage. It is the voltage developed by any source of electrical energy.
7. What is the consequence of motor effect?
c) Electromagnetic induction
Explanation: Motor effect is when a current carrying conductor in a magnetic field experiences a force, hence its consequence is electromagnetic induction.
8. The total number of magnetic field lines passing through an area is termed as?
c) Magnetic flux
d) Magnetic flux density
Explanation: The number of magnetic flux lines per unit area is the magnetic flux, because flux is the number of field lines per unit area.
9. In an A.C. generator, increase in number of turns in the coil _________
a) Increases emf
b) Decreases emf
c) Makes the emf zero
d) Maintains the emf at a constant value
Explanation: In an A.C. generator, the emf increases as the number of turns in the coil increases because the emf is directly proportional to the number of turns.
10. Find the length of a conductor which is moving with a velocity 0.4m/s in a magnetic field of 8T, inducing an emf of 20V.
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of B, emf and v from the question, we get l=6.25m.
Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.
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