Free Charged Particle in a Magnetic Field MCQs with Answers

• A. maximum magnitude
• B. zero
• C. half the maximum
• D. qvB

Explanation: The magnetic force is qvB sin theta, and sin 0 is zero, so a charge travelling along the field lines feels nothing at all.

• A. a straight line
• B. a parabola
• C. a circular path
• D. a spiral of increasing radius

Explanation: The magnetic force is always perpendicular to the velocity, so it changes direction without changing speed, which is exactly the condition…

• A. very small
• B. always perpendicular to the velocity
• C. always opposite to the velocity
• D. not a real force

Explanation: Work is the dot product of force and displacement, and a force at right angles to the motion contributes nothing, so the kinetic energy…

• A. r equals qB over mv
• B. r equals mv over qB
• C. r equals mvB over q
• D. r equals qvB

Explanation: Equating the magnetic force qvB to the required centripetal force mv squared over r and rearranging gives r equal to mv over qB.

• A. heavier ions move faster
• B. heavier ions follow a path of larger radius in the magnetic field
• C. lighter ions are stopped by the field
• D. heavier ions lose their charge

Explanation: The radius mv over qB is proportional to mass when charge, speed and field are fixed, so heavier ions curve less sharply and strike the…

• 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. 2πm/qB
• B. 2πm/qBr
• C. qrB/m
• D. 2πmq/rB
• E. 2mq/rB

Explanation: The correct answer is Option A: 2πm/qB. When a charged particle moves in a magnetic field, the magnetic force acts as the centripetal…

• A. 9.1 x 10^-3 m
• B. 9.1 x 10^-2 m
• C. 1.9 x 10^-3 m
• D. 1.9 x 10^-2 m
• E. 9.1 x 10^-1 m

Explanation: The radius of the orbit of an electron moving in a uniform magnetic field is given by the equation: r = mv/eB Where r is the radius of the…

• A. F = Qb
• B. F = qB2
• C. F = qB/v
• D. F = qvB

Explanation: This is a standard answer. A charged particle moving perpendicular to a constant magnetic field experiences a magnetic force F, which…

• A. Reflecting force
• B. Restoring force
• C. Deflecting force
• D. Gravitational force

Explanation: Magnetic force is simply a deflecting force. It will change the direction of charge particle moving in magnetic field.

• A. Charged positive particles
• B. Charged negative particles
• C. Neutral particles
• D. All of these

Explanation: Correct option is C. Magnetic fields will not be produced in case of neutral particles.

• A. Moving charge
• B. Charge in magnetic flux
• C. Current flowing in conductor
• D. Stationary charge

Explanation: A magnetic field does not affect a stationary charge because it has no velocity.

• A. Parabolic
• B. Circular
• C. Parallel to v
• D. Parallel to B

Explanation: Option A) Parabolic is not correct because a parabolic path would require an additional force acting on the charged particle, which is not…

• A. Decreases
• B. Increases then decreases
• C. Becomes zero
• D. Remains constant

Explanation: Option A : When a charged particle enters a magnetic field, its K.E. not decreases.