# Electromagnetics MCQs With Answers: Topic Wise: Part 4

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 Reluctance, electromagnetics induction, Direction of induced EMF.

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

“Reluctance”.

1. Reciprocal of reluctance is __________
a) Permeance
b) Susceptibility
c) Resistance
d) Conductance
Explanation: The reciprocal of reactance is permeance. It is the ability of a material to allow the passage of magnetic lines of flux.

2. Reactance is ________________ to the length of the material.
a) Directly proportional
b) Inversely proportional
c) Not related
d) Depends on the area of the material
Explanation: The formula for reluctance is:
S= l/∫0 ∫rA.
From the formula, we can see that reluctance is directly proportional to the length of the material.

3. Reactance is ________________ to the area of cross section the material.
a) Directly proportional
b) Inversely proportional
c) Not related
d) Depends on the length of the material
Explanation: The formula for reluctance is:

“Reluctance”.

1. Reciprocal of reluctance is __________
a) Permeance
b) Susceptibility
c) Resistance
d) Conductance
Explanation: The reciprocal of reactance is permeance. It is the ability of a material to allow the passage of magnetic lines of flux.

2. Reactance is ________________ to the length of the material.
a) Directly proportional
b) Inversely proportional
c) Not related
d) Depends on the area of the material
Explanation: The formula for reluctance is:
S= l/∫0 ∫rA.
From the formula, we can see that reluctance is directly proportional to the length of the material.

3. Reactance is ________________ to the area of cross section the material.
a) Directly proportional
b) Inversely proportional
c) Not related
d) Depends on the length of the material
Explanation: The formula for reluctance is:

S= l/∫0 ∫rA.
From the formula, we can see that reluctance is inversely proportional to the area of cross section of the material.

4. When the length of the material increases, what happens to reluctance?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero
Explanation: Reluctance is directly proportional to the length of the material hence as length increases, reluctance also increases.

5. When the area of cross section of the material increases, what happens to reluctance?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero
Explanation: Reluctance is inversely proportional to the area of cross section of the material hence as area increases, reluctance decreases.

6. Unit of reluctance is?
a) AWb
b) A2/Wb
c) Wb/A
d) A/Wb
Explanation: Reluctance is the force per unit flux, hence its unit is A/Wb.

7. The electrical equivalent of reluctance is?
a) Resistance
b) Inductance
c) Capacitance
d) Conductance
Explanation: Resistance is the opposition to the flow of charge, similarly reluctance is the opposition to the flow of magnetic flux.

8. As the magnetic field strength increases, reluctance?
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero

Explanation: Reluctance is directly proportional to the strength of magnetic field, hence as the strength of magnetic field increases, the reluctance increases.

9. As the magnetic flux density increases, the reluctance _____________
a) Increases
b) Decreases
c) Remains the same
d) Becomes zero
Explanation: Reluctance is inversely proportional to the magnetic flux density, hence as magnetic flux density increases, reluctance decreases.

10. Calculate the reluctance when the magnetomotive force is 10A turns and the flux is 5Wb.
a) 0.5A/Wb
b) 5A/Wb
c) 10A/Wb
d) 2A/Wb
Explanation: We know that:
F=phi*S
Substituting the given values from the question:
S=2A/Wb.

“Electromagnetic Induction”.

1. 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: It 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.

2. What happens to the current in a coil while accelerating a magnet inside it?
a) Increases
b) Decreases
c) Remains constant
d) Reverses
Explanation: A chance in magnetic field induces an emf. When there is an emf, there has to be a current. Hence, when the magnet is moved inside a coil, the current in it increases.

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

4. 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
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.

5. The formula for induced emf is __________
a) emf=B2l
b) emf=Bil
c) emf=Blv
d) emf=B2v
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.

6. 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
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.

7. 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
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.

8. 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
Explanation: The formula for induced emf is: emf=Blv. Substituting the values of l, emf and v from the question, we get B=4T.

9. What does emf stand for?
a) Electronic magnetic force
b) Electromotive force
c) Electromagnetic force
d) Electromated force
Explanation: emf stands for electromotive force. It is the voltage developed by any source of electrical energy.

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

“Direction of Induced EMF”.

1. According to Faraday’s laws of electromagnetic inductance, an emf is induced in a conductor whenever?
a) The conductor is perpendicular to the magnetic field
b) Lies in the magnetic field
c) Cuts magnetic lines of flux
d) Moves parallel to the magnetic field
Explanation: An emf is induced, according to Faraday’s laws of electromagnetic inductance, whenever the conductor in a magnetic field cuts the magnetic lies of flux, varying the flux per unit area, and hence the magnetic field which induces an emf.

2. Direction of induced emf is determined by __________
a) Fleming’s left hand rule
b) Fleming’s right hand rule
d) Right hand thumb rule
Explanation: Fleming’s left hand rule stated that if the index finger points towards magnetic flux, the thumb towards the motion of the conductor, then the middle finger points towards the induced emf.

3. “The direction of an induced e.m.f. is always such that it tends to set up a current opposing the motion or the change of flux responsible for inducing that e.m.f.”, this is the statement for?
a) Fleming’s left hand rule
b) Fleming’s right hand rule
d) Lenz’s law
Explanation: The above statement is that of Lenz’s law. It is used to determine the direction of the induced emf.

4. According to Fleming’s right hand rule, the thumb points towards?
a) Current
b) E.M.F.
c) Motion of the conductor
d) Magnetic flux
Explanation: Fleming’s left hand rule stated that if the index finger points towards magnetic flux, the thumb towards the motion of the conductor, then the middle finger points towards the induced emf.

5. According to Fleming’s right hand rule, the index finger points towards?
a) Current
b) E.M.F.
c) Motion of the conductor

d) Magnetic flux
Explanation: Fleming’s left hand rule stated that if the index finger points towards magnetic flux, the thumb towards the motion of the conductor, then the middle finger points towards the induced emf.

6. According to Fleming’s right hand rule, the middle finger points towards?
a) Current
b) E.M.F.
c) Motion of the conductor
d) Magnetic flux
Explanation: Fleming’s left hand rule stated that if the index finger points towards magnetic flux, the thumb towards the motion of the conductor, then the middle finger points towards the induced emf.

7. The relation between direction of induced emf and direction of motion of the conductor is?
a) Parallel
b) Equal
c) Not related
d) Perpendicular
Explanation: According to Fleming’s right hand rule, the induced emf, the motion of the conductor and the magnetic flux are mutually perpendicular.

8. The relation between direction of induced emf and direction of magnetic flux is _______
a) Parallel
b) Equal
c) Not related
d) Perpendicular
Explanation: According to Fleming’s right hand rule, the induced emf, the motion of the conductor and the magnetic flux are mutually perpendicular.

9. The relation between direction of magnetic flux and direction of motion of the conductor is _______
a) Parallel
b) Equal
c) Not related
d) Perpendicular
Explanation: According to Fleming’s right hand rule, the induced

emf, the motion of the conductor and the magnetic flux are mutually perpendicular.

10. North pole induces __________
a) Clockwise current
b) Anti-clockwise current
c) Zero current
d) Infinite current