Chapter-4 Moving Charges and Magnetism — Online MCQ Test
PHYSICS · Grade 12 · CBSE(NCERT)
Practice Chapter-4 Moving Charges and Magnetism with a free chapter-wise online MCQ test.
This chapter covers: Biot-Savart law - Ampere's law - Lorentz force - magnetic field - solenoid - galvanometer - parallel currents.
AI-generated questions from basic to board-exam level, with instant results and explanations.
Chapter-4 Moving Charges and Magnetism — Important Questions & Answers
The Biot-Savart law gives the magnetic field due to which of the following?
- A. A stationary point charge
- B. A current-carrying conductor
- C. A permanent magnet
- D. A charged particle at rest
Answer: B. A current-carrying conductor
The Biot-Savart law specifically describes the magnetic field produced by a current-carrying conductor or a moving charge.
The Biot-Savart law specifically describes the magnetic field produced by a current-carrying conductor or a moving charge.
What is the SI unit of magnetic field strength?
- A. Ampere (A)
- B. Tesla (T)
- C. Weber (Wb)
- D. Henry (H)
Answer: B. Tesla (T)
Tesla (T) is the SI unit of magnetic field strength or magnetic flux density (B).
Tesla (T) is the SI unit of magnetic field strength or magnetic flux density (B).
Which law relates the magnetic field to the current that produces it?
- A. Coulomb's law
- B. Ampere's law
- C. Faraday's law
- D. Gauss's law
Answer: B. Ampere's law
Ampere's law states that the line integral of magnetic field around a closed loop equals μ₀ times the enclosed current.
Ampere's law states that the line integral of magnetic field around a closed loop equals μ₀ times the enclosed current.
The Lorentz force on a charged particle moving in a magnetic field is perpendicular to which of the following?
- A. Only the magnetic field
- B. Only the velocity
- C. Both the magnetic field and velocity
- D. The charge of the particle
Answer: C. Both the magnetic field and velocity
The Lorentz force F = q(v × B) is perpendicular to both the velocity vector and the magnetic field vector by definition of cross product.
The Lorentz force F = q(v × B) is perpendicular to both the velocity vector and the magnetic field vector by definition of cross product.
The magnetic field inside a long solenoid with n turns per unit length carrying current I is given by:
- A. B = μ₀I
- B. B = μ₀nI
- C. B = μ₀I/n
- D. B = nI/μ₀
Answer: B. B = μ₀nI
The magnetic field inside a solenoid is B = μ₀nI, where n is the number of turns per unit length and I is the current.
The magnetic field inside a solenoid is B = μ₀nI, where n is the number of turns per unit length and I is the current.
A charged particle enters a uniform magnetic field perpendicular to its velocity. Which statement is correct?
- A. The particle moves in a straight line
- B. The particle experiences a constant deceleration
- C. The particle moves in a circular path with constant speed
- D. The particle spirals outward with increasing speed
Answer: C. The particle moves in a circular path with constant speed
The magnetic force acts as a centripetal force perpendicular to velocity, causing circular motion at constant speed since magnetic force does no work.
The magnetic force acts as a centripetal force perpendicular to velocity, causing circular motion at constant speed since magnetic force does no work.
A charged particle moves in a circular path in a uniform magnetic field. The radius of the circular path depends on:
- A. Only the charge of the particle
- B. Only the magnetic field strength
- C. The momentum of the particle and the magnetic field strength
- D. Only the velocity of the particle
Answer: C. The momentum of the particle and the magnetic field strength
The radius r = mv/(qB), which depends on the particle's momentum (mv) and the magnetic field strength B.
The radius r = mv/(qB), which depends on the particle's momentum (mv) and the magnetic field strength B.
Compare the magnetic fields at the center of a circular loop and at a point on its axis at distance equal to its radius. Which is correct?
- A. Both fields are equal
- B. Field at center is greater
- C. Field on axis is greater
- D. Field on axis is zero
Answer: B. Field at center is greater
At center: B = μ₀I/(2r). On axis at distance r: B = μ₀Ir²/(2(r²+r²)^(3/2)) = μ₀I/(4√2r). The center field is larger.
At center: B = μ₀I/(2r). On axis at distance r: B = μ₀Ir²/(2(r²+r²)^(3/2)) = μ₀I/(4√2r). The center field is larger.
A rectangular loop ABCD with sides 3 m and 4 m carries current 5 A. It is placed in a uniform magnetic field of 2 T perpendicular to the plane. The torque on the loop is:
- A. Zero
- B. 60 N·m
- C. 120 N·m
- D. Cannot be determined without angle information
Answer: A. Zero
For a rectangular loop in a uniform field perpendicular to its plane, the forces on opposite sides cancel, giving zero net torque.
For a rectangular loop in a uniform field perpendicular to its plane, the forces on opposite sides cancel, giving zero net torque.
A current-carrying wire is bent into a shape with a straight section and a circular loop. Compared to the field from only the straight section, the total field is:
- A. Always greater
- B. Always smaller
- C. Can be either greater or smaller depending on the relative position and geometry
- D. Exactly double at all points
Answer: C. Can be either greater or smaller depending on the relative position and geometry
The loop contributes field in various directions. Depending on where the straight wire is relative to the loop, the net field can increase, decrease, or even cancel partially.
The loop contributes field in various directions. Depending on where the straight wire is relative to the loop, the net field can increase, decrease, or even cancel partially.