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Electromagnetics MCQs With Answers: Topic Wise: Part 5





Here are some important Electromagnetism topic wise MCQs with answers and explanation for sppu university exams 2020, GATE preparation, companies exams and other. This contains first 3 topics from sppu syllabus of Electromangnetics Magnitude of EMF induced in a coil, generated or induced EMF, Energy stored in an conductor.

Click to read part 1 Electromagnetism topic wise MCQs with answers and explanation

Click to read part 2 Electromagnetism topic wise MCQs with answers and explanation

Click to read part 3 Electromagnetism topic wise MCQs with answers and explanation

Click to read part 4 Electromagnetism topic wise MCQs with answers and explanation

“Magnitude of EMF Induced in a Coil”.

1. The formula for induced emf is ______
a) emf=B2l
b) emf=Bil
c) emf=Blv
d) emf=B2v
Answer: c
Explanation: The formula for induced emf is: emf=Blv, where B is the magnetic field, l is the length of the conductor and v is the velocity with which it is moving in the magnetic field.

2. Which, among the following, is the formula for induced emf?
a) e=d(phi)/dt
b) e=dt/d(phi)
c) e=t*phi
d) e=t2phi
Answer: a
Explanation: The formula foe induced emf is e=d(phi)/dt because the induced emf is the flux linkage per unit time.

3. 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.
a) 50m
b) 5m
c) 6.25m
d) 0.5m
Answer: c

 

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.

4. If a conductor 0.2m long moves with a velocity of 0.3m/s in a magnetic field of 5T, calculate the emf induced.
a) 0.3V
b) 0.03V
c) 30V
d) 3V
Answer: a
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of B, l and v from the question, we get emf=0.3V.

5. What is emf?
a) Force
b) Voltage
c) Current
d) Flux
Answer: b
Explanation: Electromotive force is not actually a force. It is basically a voltage. It is the voltage developed by any source of electrical energy.

 

6. Find the strength of magnetic field in a conductor 0.5m long moving with a velocity of 10m/s, inducing an emf of 20V.
a) 1T
b) 2T
c) 3T
d) 4T
Answer: d
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of l, emf and v from the question, we get B=4T.

7. The emf induced in a coil having N turns is?
a) e=phi/t
b) e=N*phi/t
c) e=N*phi*t
d) e=N2*phi*t
Answer: b
Explanation: The emf induced in a coil having N turns is, e=N*phi/t. This is because, the emf in a single coil is the flux linkage per unit time, that is, phi/t. Hence the flux induced in N turns is N*phi/t.

8. 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
Answer: d
Explanation: 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.

9. What is the consequence of motor effect?
a) Current
b) Voltage
c) Electromagnetic induction
d) EMF
Answer: c
Explanation: Motor effect is when a current carrying conductor in a magnetic field experiences a force, hence its consequence is electromagnetic induction.

10. The total number of magnetic field lines passing through an area is termed as _______
a) Voltage
b) EMF
c) Magnetic flux
d) Magnetic flux density
Answer: b
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.

 

“Magnitude of the Generated or Induced EMF”.

1. Which, among the following, is the formula for induced emf?
a) e=d(phi)/dt
b) e=dt/d(phi)
c) e=t*phi
d) e=t2phi
Answer: a
Explanation: The formula foe induced emf is e=d(phi)/dt because the induced emf is the flux linkage per unit time.

2. The formula for induced emf is _______
a) emf=B2l

b) emf=Bil
c) emf=Blv
d) emf=B2v
Answer: c
Explanation: The formula for induced emf is: emf=Blv, where B is the magnetic field, l is the length of the conductor and v is the velocity with which it is moving in the magnetic field.

 

3. If a conductor 0.2m long moves with a velocity of 0.3m/s in a magnetic field of 5T, calculate the emf induced.
a) 0.3V
b) 0.03V
c) 30V
d) 3V
Answer: a
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of B, l and v from the question, we get emf=0.3V.

4. 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.
a) 50m
b) 5m
c) 6.25m
d) 0.5m
Answer: c
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.

5. Find the strength of magnetic field in a conductor 0.5m long moving with a velocity of 10m/s, inducing an emf of 20V.
a) 1T
b) 2T
c) 3T
d) 4T
Answer: d
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of l, emf and v from the question, we get B=4T.

6. What is emf?
a) Force
b) Voltage
c) Current
d) Flux
Answer: b
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. 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
Answer: d
Explanation: 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.

8. The emf induced in a coil having N turns is?
a) e=phi/t
b) e=N*phi/t
c) e=N*phi*t
d) e=N2*phi*t
Answer: b
Explanation: The emf induced in a coil having N turns is, e=N*phi/t. This is because, the emf in a single coil is the flux linkage per unit time, that is, phi/t. Hence the flux induced in N turns is N*phi/t.

9. The total number of magnetic field lines passing through an area is termed as ________
a) Voltage
b) EMF
c) Magnetic flux
d) Magnetic flux density
Answer: b
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.

10. What is the consequence of motor effect?
a) Current
b) Voltage
c) Electromagnetic induction
d) EMF
Answer: c
Explanation: Motor effect is when a current carrying conductor in a magnetic field experiences a force, hence its consequence is electromagnetic induction.

“Energy Stored in an Inductor”.

1. If the current in a coil having a constant inductance of L henrys grows at a uniform rate, what is the value of the average current?
a) I
b) I/2
c) I/4
d) 0
Answer: b
Explanation: The average current is the average of the current which flows in the inductor. Hence it is I/2.

2. What is the power in the magnetic field if the current in a coil has a constant inductance of L henrys grows at a uniform rate?
a) LI/2t
b) LI2/2t
c) L/2It
d) L/2I2t
Answer: b
Explanation: The average current is I/2. The e.m.f. induced in the coil is LI/t V. Power= VI, hence the average power= I/2*LI/t.

3. What is the energy stored in the magnetic field if the current in a coil has a constant inductance of L henrys grows at a uniform rate?
a) LI/2
b) LI2/2
c) L/2I
d) L/2I2
Answer: b
Explanation: The average current is I/2. The e.m.f. induced in the coil is LI/t V. Power= VI, hence the average power= I/2*LI/t. The total energy stored= power*t= LI2/2.

4. Find the average current in an inductor if the total current in the inductor is 26A.
a) 10A
b) 26A
c) 13A
d) 5A
Answer: c
Explanation: Average current= I/2.
Substituting the value of I from the equation, average current= 13A.

5. Calculate the power in an inductive circuit if the inductance is 10H, the current flowing in the inductor is 2A in 4s.
a) 50W

b) 4W
c) 5W
d) 10W
Answer: c
Explanation: The expression for power in an inductive circuit is:
P= LI2/2
Substituting the values from the given question, we get P=5W.

6. Calculate the value of stored energy in an inductor if the value of inductance is 20H and 4A of current flows through it.
a) 220J
b) 150J
c) 190J
d) 160J
Answer: d
Explanation: The expression for energy in an inductor is:
W= LI2/2t
Substituting the values from the given question, we get W= 160J.

7. Calculate the emf induced in an inductor if the inductance is 10H and the current is 2A in 4s.
a) 2.5V
b) 1.5V
c) 3.5V
d) 5V
Answer: a
Explanation: The expression for emf in an inductive circuit is:
emf= LI/2t
Substituting the values from the given question, we get emf= 2.5V.

8. Calculate the value of emf in an inductor if the value of inductance is 15H and an average current of 5A flows through it in 10s.
a) 15V
b) 7.5V
c) 10V
d) 5.5V
Answer: b
Explanation: The expression for emf in an inductive circuit is:
emf= LI/2t, where I/2 is the average current.
Substituting the values from the given question, we get emf= 2.5V.

9. Calculate the current in an inductor if the energy stored is 160J and the inductance is 20H.
a) 1A
b) 2A
c) 3A
d) 4A
Answer: d

Explanation: The expression for energy in an inductor is:
W= LI2/2t
Substituting the values from the given question, we get I=4A.

10. Find the time taken for the current in an inductor to change to 2A from 0A if the power in the inductor is 5W. The value of inductance is 10H.
a) 1s
b) 2s
c) 3s
d) 4s
Answer: d
Explanation: The expression for power in an inductive circuit is:
P= LI2/2
Substituting the values from the given question, we get t=4s.

“Electric and Magnetic Circuits”.

1. While comparing electric and magnetic circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit?

a) E.M.F

b) Current

c) Current density

d) Conductivity

Answer: B

 

2. The unit of magnetic flux is

a)  Henry

b) Weber

c) Ampere-turn/weber

d) Ampere/meter

Answer: B

 

3. Permeability in a magnetic circuit corresponds to ______________ in an electric circuit.

a) Resistance

b) Resistivity

c) Conductivity

d) Conductance

Answer: C

 

4. Conductance is analogous to

a) Permeance

b) Reluctance

c) Flux

d) Inductance

Answer: A

 

5. Reciprocal of reluctance is

a) Reluctivity

b) Permeance

c) Permeability

d) Susceptibility

Answer: B

 

6. The unit of retentivity is

a) Weber

b) Weber/ sq.m

c) Ampere turn/meter

d) Ampere turns

Answer B

 

7. An air gap is usually inserted in magnetic circuits to

a) Increase mmf

b) Increase the flux

c) Prevent saturation

d) None of the above

Answer: C

 

8. The unit of reluctance is

a) Meter/ Henry

b) Henry/meter

c) Henry

d) 1/ Henry

Answer: D





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