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 Electromangnetism magnetomotive force and magnetic field strength, Permeability of Free Space or Magnetic Constant, Relative permeability.
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
“Magnetomotive Force and Magnetic Field Strength”.
1. What is a permeable substance?
a) Any good conductor
b) Any bad conductor
c) Any strong magnet
d) Any substance through which the magnetic lines of force can pass easily
Answer: d
Explanation: A permeable substance is one through which the magnetic lines of force can pass through easily.
2. Materials having good retentivity are?
a) Strong magnets
b) Weak magnets
c) Temporary magnets
d) Permanent magnets
Answer: c
Explanation: Materials having low retentivity are temporary magnets because they can retain the magnetic strength for only some time.
3. Magnetic field exists along which of the following?
a) Moving charges
b) Stationary charges
c) Copper
d) Iron
Answer: a
Explanation: Moving charges have a magnetic field associated with them because they have magnetic flux lines associated with it.
4. The direction of magnetic lines of force are?
a) From north pole to south pole
b) From south pole to north pole
c) No specific direction
d) From one end of the magnet to the other
Answer: a
Explanation: Magnetic lines of force originate at the north pole and terminate at the south pole hence they are from the north pole to the south pole.
5. Magnetic force lines ___________ at the north pole.
a) Emerge
b) Converge
c) Neither emerge nor converge
d) Either emerge or converge
Answer: a
Explanation: Magnetic force lines emerge at the north pole. Force lines seem to emerge at the north pole because they originate at the north pole.
6. When a bar magnet is broken into two pieces, which of the following are true?
a) The magnet loses its magnetism
b) The magnet has only north pole left
c) The magnet has only south pole left
d) The magnet turns into two new bar magnets
Answer: d
Explanation: When a bar magnet is broken into two pieces, it forms two differ bar magnets. This happens because the broken pieces of the magnet forms a separate north and south pole for itself as monopoles do not exist.
7. When an electric current flows into the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current
Answer: a
Explanation: when the current flows into the page, the magnetic field is clockwise because of the right hand thumb rule, we orient our thumb into the page and our fingers curl in the clockwise direction.
8. When an electric current flows out of the page, what is the direction of the magnetic field?
a) Clockwise
b) Anti-clockwise
c) Cannot be determined
d) Parallel to the current
Answer: b
Explanation: when the current flows out of the page, the magnetic field is anti-clockwise because of the right hand thumb rule, we orient our thumb out of the page and our fingers curl in the anti-clockwise direction.
9. Which of the following is used to determine the direction of magnetic field in a current carrying conductor?
a) Left hand thumb rule
b) Right hand thumb rule
c) Right hand palm rule
d) Left hand palm rule
Answer: b
Explanation: The right hand thumb rule determines the direction of magnetic field in a current carrying conductor. The rule states that when we align our right thumb in the direction of the current and curl our fingers around it, the direction of our fingers is the direction of the magnetic field.
10. The relation between the direction of current and the direction of magnetic field is?
a) Same direction
b) Opposite direction
c) Perpendicular
d) Unrelated
Answer: c
Explanation: When a conductor carries a certain value of current, the force developed in the conductor, the current in the conductor and the magnetic field in the conductor are mutually perpendicular to each other.
“Permeability of Free Space or Magnetic Constant”.
1. Permeability of free space is also known as _________
a) Magnetic constant
b) Electric constant
c) Electrostatic constant
d) Magnetostatic constant
Answer: a
Explanation: The permeability of free space is also known as magnetic constant. The permittivity of free space is the electrostatic constant.
2. A substance whose permeability is less than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: a
Explanation: A diamagnetic material creates a magnetic field
opposing that of the external magnetic field and it repels the external magnetic field. Hence its permeability is less than that of free space.
3. Which, among the following, have negative susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: a
Explanation: Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Diamagnetic substances repel the magnetic field and hence have negative susceptibility.
4. Which, among the following, have positive susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: b
Explanation: Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Paramagnetic substances weakly attract to the magnetic field and hence have positive susceptibility.
5. A substance whose permeability is more than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: b
Explanation: A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence its permeability is more than that of free space.
6. The unit for permeability of free space is?
a) Henry
b) Henry-m
c) Henry/m
d) Henry/m2
Answer: c
Explanation: Magnetic permeability is the constant of proportionality between the magnetic flux density and magnetic field strength of a given medium. Hence it has units henry/m.
7. Which, among the following, is a correct expression for ∫0.
a) ∫0=BH
b) ∫0=B/H
c) ∫0=H/B
d) ∫0=BH2
Answer: b
Explanation: Magnetic permeability is the constant of proportionality between the magnetic flux density and magnetic field strength of a given medium. Hence ∫0=B/H.
8. Calculate the magnetic flux density if the magnetic field strength is 2A/m.
a) 4*pi/10-7T
b) 8*pi/10-7T
c) 10*pi/10-7T
d) 12*pi/10-7T
Answer: b
Explanation: We know that:
∫0=B/H
Substituting the value of H from the question, we get B= 8*pi/10-7T.
9. Calculate the magnetic field strength if the magnetic flux density is 4*piT.
a) 10-7/16*pi2A/m
b) 10-7A/m
c) 107A/m
d) 10-7A
Answer: c
Explanation: We know that:
∫0=B/H
Substituting the value of B from the question, we get H = 107A/m.
10. Calculate the magnetic flux density if the magnetic field strength is 3A/m.
a) 4*pi/10-7T
b) 8*pi/10-7T
c) 10*pi/10-7T
d) 12*pi/10-7T
Answer: d
Explanation: We know that:
∫0=B/H
Substituting the value of H from the question, we get B= 12*pi/10-7T.
“Relative Permeability”
1. What is the unit for relative permeability?
a) H-m
b) H/m
c) H2/m
d) No unit
Answer: d
Explanation: Relative permeability is the ratio of permeability of the material to the permeability of free space. Since it is a ratio, it does not have any units.
2. Which of the following expressions is correct with respect to relative permeability?
a) B=∫r∫0/H
b) B=∫r∫0H
c) B=∫r/∫0H
d) B=∫r∫0/H2
Answer: b
Explanation: For a non magnetic material: B=∫0H. Hence for a material having relative permeability ∫r, B=∫r∫0H.
3. A substance whose relative permeability is less than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: a
Explanation: A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence its relative permeability is less than that of the free space.
4. A substance whose relative permeability is more than the permeability of free space is?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: b
Explanation: A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence its permeability is more than that of free space.
5. Diamagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero
Answer: b
Explanation: A diamagnetic material creates a magnetic field opposing that of the external magnetic field and it repels the external magnetic field. Hence it has relative permeability less than 1.
6. Paramagnetic substances have relative permeability_____________
a) Greater than 1
b) Less than 1
c) Equal to 1
d) Zero
Answer: a
Explanation: A paramagnetic material creates a magnetic field which is weakly attracted to that of the external magnetic field. Hence it has relative permeability greater than 1.
7. As the temperature increases up to the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
Answer: a
Explanation: The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the Curie temperature.
8. As the temperature increases beyond the Curie temperature, the relative susceptibility of ferromagnetic materials?
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
Answer: b
Explanation: The susceptibility of ferromagnetic materials increases with the increase in temperature and then it decreases when the temperature goes beyond the curie temperature.
9. Which, among the following, have positive susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: b
Explanation: Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Paramagnetic
substances weakly attract to the magnetic field and hence have positive susceptibility.
10. Which, among the following, have negative susceptibility?
a) Diamagnetic
b) Paramagnetic
c) Ferromagnetic
d) Not a magnetic substance
Answer: a
Explanation: Magnetic susceptibility is the degree of magnetisation of a material in response to the external magnetic field. Diamagnetic substances repel the magnetic field and hence have negative susceptibility.
