Free Electromagnetism MCQs with Answers

• A. a straight line parallel to the field
• B. a parabola in a plane perpendicular to the field
• C. a circle in a plane perpendicular to the field
• D. a straight line along its initial direction

Explanation: For velocity perpendicular to the magnetic field, the magnetic force qvB is always perpendicular to the velocity and acts as centripetal…

• A. a circle
• B. a spiral
• C. an ellipse
• D. helix

Explanation: The velocity component perpendicular to the field produces circular motion, while the component parallel to the field remains uniform.

• A. R=qB/mV
• B. R=mV/qB
• C. R=qmV/B
• D. R=qmB/V

Explanation: The magnetic force supplies centripetal force: qvB = mv^2/r. Rearranging gives r = mv/(qB), with radius r in m, mass m in kg, velocity v…

• A. E = BeV
• B. B = eE/V
• C. E = BV
• D. E = BeV/2

Explanation: For no deflection, the electric and magnetic forces must be equal: eE = evB, so E = vB.

• A. always exerts a force on a charged particle
• B. never exerts a force on a charged particles
• C. exerts a force if the charged particle is moving in the direction of the magnetic field lines
• D. exerts a force if the charged particle is moving perpendicular to the magnetic field lines

Explanation: The magnetic force is F = qvB sin θ, so it is greatest when a charged particle moves perpendicular to the magnetic field lines.

• A. Plasma physics
• B. Electro-static's
• C. Electro-magnetic
• D. Electro-dynamics

Explanation: Electrodynamics deals with electric charges in motion and the electric and magnetic fields associated with them.

• A. Elementary articles
• B. Article physics
• C. Ionic physics
• D. Plasma physics

Explanation: Plasma physics studies highly ionised matter containing free electrons and ions, often at very high energies.

• A. One gauss
• B. 3×10¹⁰ gauss
• C. 10⁴ gauss
• D. 1/3×10^-8 gauss

Explanation: Magnetic flux density is measured in tesla, and 1 tesla = 1 weber/m². Since 1 gauss = 10^-4 tesla, 1 weber/m² = 1 tesla = 10^4 gauss.

• A. Semiconductors
• B. Insulators
• C. Conductors
• D. None of these

Explanation: Ceramic magnets are made from ferrite materials, which have high electrical resistance and therefore behave as insulators.

• A. Magnetic intensity
• B. Magnetic moment
• C. Magnetic induction
• D. None of the above

Explanation: The tesla (T) is the SI unit of magnetic flux density, also called magnetic induction, B.

• A. repel each other
• B. not interact with each other
• C. attract each other
• D. be deflected normal to the plane containing the two beams.Educational Resources

Explanation: Two parallel beams of positrons produce electric repulsion because both beams carry positive charge.

• A. weaken it
• B. strengthen it
• C. reverse its polarity
• D. demagnetize it completely

Explanation: Heating disturbs the alignment of magnetic domains, so the magnet becomes weaker.

• A. 4πx10-9 WbA-1m-1
• B. 4πx10-7 WbA-1m-1
• C. 4πx10-10 WbA-1m-1
• D. 4πx10-8 WbA-1m-1

Explanation: The permeability of free space is μ0 = 4π x 10^-7 Wb A^-1 m^-1, equivalently N A^-2. The powers of ten in the other choices are incorrect.

• A. τ = NIAB cosφ
• B. τ = NIAB sinφ
• C. τ = NIAB tanφ
• D. τ = NIAB

Explanation: The torque on a current-carrying coil is τ = NIAB sinθ, where θ is the angle between the coil's normal and the magnetic field.

• A. charge in motion
• B. charge at rest
• C. both
• D. none

Explanation: A moving charge produces a magnetic field, and that field can exert torque on the magnetic needle of a compass.

• A. F=1/B
• B. F=1/Bsinθ
• C. F/0
• D. F=1/Bcosθ

Explanation: The magnetic force on a current-carrying conductor is F = BIL sinθ. When the conductor is parallel to the field, θ = 0° and sin0° = 0, so…

• A. be rotating
• B. come to rest in N-S direction
• C. vibrating like galvanometer needle
• D. comes to rest after rotation

Explanation: A current-carrying solenoid behaves like a bar magnet, so its magnetic dipole aligns itself with Earth's magnetic field when freely…

• A. BINA cosa
• B. BINA sina
• C. BINA tana
• D. BINA

Explanation: The deflecting torque on a current-carrying coil is τ = BINA sin α. In a radial magnetic field, the field is always effectively…

• A. NA-1m-1
• B. NAm-1
• C. NmA-1
• D. NmA-2

Explanation: Magnetic flux density has the SI unit tesla, and 1 T = 1 N A^-1 m^-1. Students may choose d, N m A^-2, because it is dimensionally…

• A. 1T = 103 G
• B. 1T = 10-4 G
• C. 1T = 10-2 G
• D. 1T = 104 G

Explanation: The conversion is 1 tesla = 10,000 gauss = 10^4 G, so option d is correct.