List of top Physics Questions on Moving Charges and Magnetism asked in CBSE CLASS XII

What is the source of force acting on a current-carrying conductor placed in a magnetic field? Obtain the expression for the force acting between two long straight parallel conductors carrying steady currents and hence define Ampère’s law.
Two infinitely long conductors kept along XX' and YY' axes are carrying current \( I_1 \) and \( I_2 \) along -X axis and -Y axis respectively. Find the magnitude and direction of the net magnetic field produced at point P(X, Y).
A 1 cm straight segment of a conductor carrying 1 A current in \( x \)-direction lies symmetrically at the origin of Cartesian coordinate system. The magnetic field due to this segment at point (1m, 1m, 0) is:
Write two characteristics of equipotential surfaces. A uniform electric field of 50 NC\(^{-1}\) is set up in a region along the \( x \)-axis. If the potential at the origin \( (0, 0) \) is 220 V, find the potential at a point \( (4m, 3m) \).
A point charge \( q \) is moving with velocity \( \mathbf{v} \) in a uniform magnetic field \( \mathbf{B} \). Find the work done by the magnetic force on the charge.
Find the value of \( v_0 \) in terms of \( E \), \( d \), and \( I \).
What are the various forces acting on the charged particle?
In a region of a uniform electric field \( \mathbf{E} \), a negatively charged particle is moving with a constant velocity \( \mathbf{v} = -v_0 \hat{i} \) near a long straight conductor coinciding with XX' axis and carrying current \( I \) towards -X axis. The particle remains at a distance \( d \) from the conductor.
Obtain an expression for the torque \( \tau \) acting on a current-carrying loop in a uniform magnetic field \( \vec{B} \). Draw the necessary diagram.
Explain the necessary conditions in which the trajectory of a charged particle is helical in a uniform magnetic field.
In a hydrogen atom, the electron moves in an orbit of radius \( 2 \, \text{Å} \) making \( 8 \times 10^{14} \) revolutions per second. Find the magnetic moment associated with the orbital motion of the electron.
A particle of mass \( m \) and charge \( q \) is moving with a velocity \( \vec{v} \) in a magnetic field \( \vec{B} \) as shown in the figure. Show that it follows a helical path. Hence, obtain its frequency of revolution.
charged particle in a magnetic field
 
Two long, straight, parallel conductors carry steady currents in opposite directions. Explain the nature of the force of interaction between them. Obtain an expression for the magnitude of the force between the two conductors. Hence define one ampere.
Assertion (A): An electron and a proton enter with the same momentum \( \vec{p} \) in a magnetic field \( \vec{B} \) such that \( \vec{p} \perp \vec{B} \). Then both describe a circular path of the same radius.
Reason (R): The radius of the circular path described by the charged particle (charge \( q \), mass \( m \)) moving in the magnetic field \( \vec{B} \) is given by \( r = \frac{mv}{qB} \).
A wire of length 4.4 m is bent round in the shape of a circular loop and carries a current of 1.0 A. The magnetic moment of the loop will be:
(a) A circular coil of 30 turns and radius 8.0 cm carrying a current of 6.0 A is suspended vertically in a uniform horizontal magnetic field of magnitude 1.0 T. The field lines make an angle of 60° with the normal of the coil. Calculate the magnitude of the counter torque that must be applied to prevent the coil from turning. 
(b) Would your answer change, if the circular coil in (a) were replaced by a planar coil of some irregular shape that encloses the same area? (All other particulars are also unaltered.)
In a chamber, a uniform magnetic field of \(6.5 \,G \,(1 G = 10^ {–4 }T)\) is maintained. An electron is shot into the field with a speed of \(4.8 × 10^6\, m s^{–1}\) normal to the field. Obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain.\((e = 1.5 × 10^{–19}C,\, m_e = 9.1×10^{–31} kg)\)
A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?
A 3.0 cm wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be 0.27 T. What is the magnetic force on the wire?
Two moving coil meters, \(M_1\) and \(M_2\) have the following particulars:
\(R_1\) =\(10\,\Omega\) , \(N_1\) = 30,
\(A_1\) = \(3.6 × 10^{–3} m^2\), \(B_1\) = \(0.25\, T\) 
\(R_2\) = \(14 \,\Omega\), \(N_2\) = 42,
\(A_2\) = \(1.8 × 10^{–3 }m^2 \), \(B_2\) = \(0.50 T \)
(The spring constants are identical for the two meters).
Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of \(M_2\) and \(M_1\).
In a chamber, a uniform magnetic field of \(6.5\, G \,(1 G = 10 ^{–4} T)\) is maintained. An electron is shot into the field with a speed of \(4.8 × 10^6 m s^{–1 }\) normal to the field. Explain why the path of the electron is a circle. Determine the radius of the circular orbit. \((e = 1.5 × 10^{–19} C, m_e = 9.1×10^{–31} kg)\)
A square coil of side 10 cm consists of 20 turns and carries a current of 12 A. The coil is suspended vertically and the normal to the plane of the coil makes an angle of \(30\degree\) with the direction of a uniform horizontal magnetic field of magnitude 0.80 T. What is the magnitude of torque experienced by the coil?
A closely wound solenoid 80 cm long has 5 layers of windings of 400 turns each. The diameter of the solenoid is 1.8 cm. If the current carried is 8.0 A, estimate the magnitude of B inside the solenoid near its centre.
Two long and parallel straight wires A and B carrying currents of 8.0 A and 5.0 A in the same direction are separated by a distance of 4.0 cm. Estimate the force on a 10 cm section of wire A.
What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A and making an angle of 30º with the direction of a uniform magnetic field of 0.15 T?