Physics Grade 12 Unit 4 Electromagnetism MCQs with explanation
PART 1
1. A freely suspended bar magnet rest in:
A. North-South direction
B. East-west direction
C. North-East direction
D. South-East direction
Answer A
A freely suspended bar magnet always rests in North-south direction because the North pole of the magnet lies in the geographic North direction and the south pole of the magnet lies in the geographic south direction. So, it aligns itself in N-S direction. As unlike poles attract and like poles repel.
2. Which one of the following is not true about the motion of charged particle in a uniform magnetic
field?
A. Magnetic force changes only the direction of the charge and the speed of the particle stays
constant.
B. The force experienced by the charged particle is only the centripetal force
C. The force is zero when the particle moves along the field lines
D. The force does maximum work when the charge moves perpendicular to the magnetic field strength
Answer D.
The magnetic force on a charged particle always acts perpendicular to the particle's velocity, so it cannot do work (as work requires a force component in the direction of motion).
3. A charged particle is moving in a magnetic field. What is the direction of the force on the particle due to the magnetic field?
A. in the direction of the magnetic field
B. in the direction opposite to which the particle is moving
C. in the direction that is perpendicular to both the magnetic field and the velocity
D. in the same plane as the magnetic field and the velocity, but not in either of those two
directions
Answer C.
Explanation:
The force on a charged particle moving in a magnetic field is given by
𝐹 = 𝑞(𝑣𝐵⃗ ) The direction of the force is perpendicular to both the velocity of the particle and the magnetic field, as determined by the right-hand rule. This means the force is always at a right angle to both the direction of motion and the magnetic field.
4. An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy.
Which of the following is true?
A. Trajectory of electron is less curved
B. Trajectory of proton is less curved
C. Both trajectories are equally curved
D. Both move on straight line path
Answer B. Trajectory of proton is less curved.
5. Magnetic fields can be pictorially represented by magnetic field lines, which one of the following is not true about the properties of these field lines?
A. The field is tangent to the magnetic field line.
B. Field strength is proportional to the line density.
C. Field lines can cross each other.
D. Field lines are continuous loops.
Answer C
Explanation
=> Magnetic field lines are cannot cross each other.
=> Form closed loops.
=> No beginning or end points; they are continuous.
=> The field strength is stronger where the lines are closer together
=> Direction is from the north pole to the south pole outside the magnet, and inside the magnet from south to north
Part 2 Continued.......
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PART 1
1. A freely suspended bar magnet rest in:
A. North-South direction
B. East-west direction
C. North-East direction
D. South-East direction
Answer A
A freely suspended bar magnet always rests in North-south direction because the North pole of the magnet lies in the geographic North direction and the south pole of the magnet lies in the geographic south direction. So, it aligns itself in N-S direction. As unlike poles attract and like poles repel.
2. Which one of the following is not true about the motion of charged particle in a uniform magnetic
field?
A. Magnetic force changes only the direction of the charge and the speed of the particle stays
constant.
B. The force experienced by the charged particle is only the centripetal force
C. The force is zero when the particle moves along the field lines
D. The force does maximum work when the charge moves perpendicular to the magnetic field strength
Answer D.
The magnetic force on a charged particle always acts perpendicular to the particle's velocity, so it cannot do work (as work requires a force component in the direction of motion).
3. A charged particle is moving in a magnetic field. What is the direction of the force on the particle due to the magnetic field?
A. in the direction of the magnetic field
B. in the direction opposite to which the particle is moving
C. in the direction that is perpendicular to both the magnetic field and the velocity
D. in the same plane as the magnetic field and the velocity, but not in either of those two
directions
Answer C.
Explanation:
The force on a charged particle moving in a magnetic field is given by
𝐹 = 𝑞(𝑣𝐵⃗ ) The direction of the force is perpendicular to both the velocity of the particle and the magnetic field, as determined by the right-hand rule. This means the force is always at a right angle to both the direction of motion and the magnetic field.
4. An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy.
Which of the following is true?
A. Trajectory of electron is less curved
B. Trajectory of proton is less curved
C. Both trajectories are equally curved
D. Both move on straight line path
Answer B. Trajectory of proton is less curved.
5. Magnetic fields can be pictorially represented by magnetic field lines, which one of the following is not true about the properties of these field lines?
A. The field is tangent to the magnetic field line.
B. Field strength is proportional to the line density.
C. Field lines can cross each other.
D. Field lines are continuous loops.
Answer C
Explanation
=> Magnetic field lines are cannot cross each other.
=> Form closed loops.
=> No beginning or end points; they are continuous.
=> The field strength is stronger where the lines are closer together
=> Direction is from the north pole to the south pole outside the magnet, and inside the magnet from south to north
Part 2 Continued.......
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