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MP Board Class 12 (MPBSE) Moving Charges and Magnetism — practice questions

Explore 61 free Moving Charges and Magnetism questions in MP Board Class 12 (MPBSE) Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Moving Charges and Magnetism questions and exercises with answers

Showing questions 1–30 of 61.

A long straight wire carries $5$ A. The magnetic field $0.10$ m away from the wire is:Read the answer and worked solution →The magnetic force on a charge $q$ moving with velocity $\vec{v}$ in a magnetic field $\vec{B}$ isRead the answer and worked solution →A positive charge moves with velocity $\vec{v}$ PARALLEL to a uniform magnetic field $\vec{B}$. The magnetic force on it isRead the answer and worked solution →The magnetic field at the CENTRE of a circular current loop of radius $R$ carrying current $I$ isRead the answer and worked solution →Inside a long solenoid carrying current $I$ with $n$ turns per unit length, the magnetic field isRead the answer and worked solution →A current loop of area $A$ carrying current $I$ has a MAGNETIC MOMENT of magnitudeRead the answer and worked solution →The magnetic field at a distance $r$ from a LONG STRAIGHT wire carrying current $I$ isRead the answer and worked solution →A charged particle moves with velocity v parallel to a uniform magnetic field B. The magnetic force on the particle isRead the answer and worked solution →A circular loop of radius R carries current I. The magnitude of the magnetic field at its centre isRead the answer and worked solution →The angular frequency of a particle of charge q and mass m moving in a cyclotron with magnetic field B isRead the answer and worked solution →Two long parallel wires carry currents in the same direction. They willRead the answer and worked solution →The magnetic field inside an ideal long solenoid with n turns per unit length carrying current I isRead the answer and worked solution →In a crossed E and B velocity selector, a charged particle of speed v passes undeflected when v equalsRead the answer and worked solution →A proton of mass m, charge e, speed v enters a magnetic field B perpendicular to its velocity. The radius of its circular path isRead the answer and worked solution →A rectangular current loop is placed in a uniform magnetic field. The net force on the loop isRead the answer and worked solution →A circular coil of N turns and radius R carries current I. Its magnetic dipole moment isRead the answer and worked solution →The magnitude of the magnetic field at perpendicular distance r from an infinite straight wire carrying current I isRead the answer and worked solution →The magnetic field inside a toroidal solenoid with N total turns, mean radius r, carrying current I isRead the answer and worked solution →The period of revolution of a charged particle moving in a uniform magnetic field perpendicular to its velocity isRead the answer and worked solution →A 0.5 m wire carrying 2 A is placed perpendicular to a 0.4 T magnetic field. The force on the wire isRead the answer and worked solution →Two long parallel wires 0.1 m apart carry 5 A and 10 A in the same direction. The force per unit length on each wire isRead the answer and worked solution →At equilibrium, the deflection ϕ of a moving coil galvanometer with N turns, area A, current I, in a radial magnetic field B and spring constant k satisfiesRead the answer and worked solution →An electron enters a uniform magnetic field B at angle θ to B with speed v. The pitch of its helical path isRead the answer and worked solution →A cyclotron of dee radius R accelerates ions of charge q, mass m in a magnetic field B. The maximum kinetic energy isRead the answer and worked solution →A circular loop of radius R carries current I. The magnetic field at a point on its axis at distance x from the centre isRead the answer and worked solution →At the very end of a long solenoid, the magnetic field along the axis isRead the answer and worked solution →A magnetic dipole with moment m makes angle θ with a uniform field B. The torque on the dipole has magnitudeRead the answer and worked solution →An electron moves east in a magnetic field directed north. The magnetic force on the electron pointsRead the answer and worked solution →A cyclotron operates at frequency f in a magnetic field B. The charge-to-mass ratio of the accelerated ion isRead the answer and worked solution →The current sensitivity of a moving coil galvanometer with N turns, coil area A, magnetic field B, spring constant k isRead the answer and worked solution →

Worked practice questions

A long straight wire carries $5$ A. The magnetic field $0.10$ m away from the wire is:

  1. $1.0\times 10^{-5}$ T, by $B = \mu_0 I/(2\pi r)$
  2. $5\times 10^{-7}$ T, ignoring the $2\pi$ factor here
  3. $1.0$ T, ignoring all scaling on the formula
  4. Zero, since the wire is straight, not coiled
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Correct answer: A. $1.0\times 10^{-5}$ T, by $B = \mu_0 I/(2\pi r)$

$B = 4\pi\times 10^{-7}\cdot 5/(2\pi\cdot 0.1) = 1.0\times 10^{-5}$ T.

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The magnetic force on a charge $q$ moving with velocity $\vec{v}$ in a magnetic field $\vec{B}$ is

  1. $q\vec{v} + \vec{B}$
  2. $q\vec{v}\cdot\vec{B}$
  3. $q\vec{v}\times\vec{B}$
  4. $\vec{v}/(qB)$
Show answer and solution

Correct answer: C. $q\vec{v}\times\vec{B}$

1. Your syllabus: the Lorentz magnetic force is $\vec{F} = q\vec{v}\times\vec{B}$. 2. The cross product means $\vec{F}$ is perpendicular to BOTH $\vec{v}$ and $\vec{B}$. 3. Magnitude: $F = q v B \sin\theta$, where $\theta$ is the angle between $\vec{v}$ and $\vec{B}$. 4. Direction: by the right-hand rule (point fingers along $\vec{v}$, curl toward $\vec{B}$, thumb gives $\vec{F}$ direction for positive $q$; reverse for negative $q$). 5. Option A has wrong dimensions (mixing $qv$ and $\vec{B}$). Option B is the dot product (a scalar, not a force vector). Option D is gibberish dimensionally. _Source: syllabus Physics Part 1, Ch 4, §4.2 (Magnetic Force, Eq. 4.4), p. 2–3._

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A positive charge moves with velocity $\vec{v}$ PARALLEL to a uniform magnetic field $\vec{B}$. The magnetic force on it is

  1. $qvB$ (maximum)
  2. $\dfrac{1}{2}\,qvB$
  3. $qvB / \sqrt{2}$
  4. zero
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Correct answer: D. zero

1. The magnetic force magnitude is $F = qvB\sin\theta$, where $\theta$ is the angle between $\vec{v}$ and $\vec{B}$. 2. When $\vec{v}\parallel\vec{B}$, $\theta = 0$ and $\sin 0 = 0$. 3. So $F = 0$. The charge experiences no magnetic force when its velocity is parallel (or antiparallel) to the field. 4. Consequence: a charged particle moving along magnetic field lines is unaffected by the field — explains why charged particles streaming along Earth's magnetic field lines can reach the poles (aurora). 5. Option A is for $\theta = 90^\circ$. Options B and C correspond to specific intermediate angles ($30^\circ$, $45^\circ$). _Source: syllabus Physics Part 1, Ch 4, §4.2 (Magnetic Force — perpendicular dependence), p. 2–3._

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