List of top Physics Questions on Electromagnetic Field (EMF)

Due to presence of an em-wave whose electric component is given by $ E = 100 \sin(\omega t - kx) \, NC^{-1} $, a cylinder of length 200 cm holds certain amount of em-energy inside it. If another cylinder of same length but half diameter than previous one holds same amount of em-energy, the magnitude of the electric field of the corresponding em-wave should be modified as:

A solenoid having area $ A $ and length $ \ell $ is filled with a material having relative permeability 2. The magnetic energy stored in the solenoid is:

In the first configuration (1) as shown in the figure, four identical charges $ q_0 $ are kept at the corners A, B, C and D of square of side length $ a $. In the second configuration (2), the same charges are shifted to mid points C, E, H, and F of the square. If $ K = \frac{1}{4\pi \epsilon_0} $, the difference between the potential energies of configuration (2) and (1) is given by:

A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of $ 2 \times 10^5 \, \text{m/s} $. When the electric field is switched off, the proton moves along a circular path of radius 2 cm. The magnitude of electric field is $ x \times 10^4 \, \text{N/C} $. The value of $ x $ is $\_\_\_\_\_$. (Take the mass of the proton as $ 1.6 \times 10^{-27} \, \text{kg} $).

The Lagrangian of a particle of mass $ m $ and charge $ q $ moving in a uniform magnetic field of magnitude $ 2B $ that points in the $ z $-direction, is given by: \[ L = \frac{m}{2} v^2 + qB(x v_y - y v_x) \] where $ v_x, v_y, v_z $ are the components of its velocity $ v $. If $ p_x, p_y, p_z $ denote the conjugate momenta in the $ x, y, z $-directions and $ H $ is the Hamiltonian, which of the following option(s) is/are correct?

In the first configuration (1) as shown in the figure, four identical charges $ q_0 $ are kept at the corners A, B, C and D of square of side length $ a $. In the second configuration (2), the same charges are shifted to mid points C, E, H, and F of the square. If $ K = \frac{1}{4\pi \epsilon_0} $, the difference between the potential energies of configuration (2) and (1) is given by:

The fractional compression $ \frac{\Delta V}{V} $ of water at the depth of 2.5 km below the sea level is:

Due to the presence of an em-wave whose electric component is given by $ E = 100 \sin(\omega t - kx) \, \text{N/C} $, a cylinder of length 200 cm holds a certain amount of em-energy inside it. If another cylinder of the same length but half the diameter of the previous one holds the same amount of em-energy, the magnitude of the electric field of the corresponding em-wave should be modified as:

A square loop of side 15 cm being moved towards right at a constant speed of 2 cm/s as shown in figure. The front edge enters the 50 cm wide magnetic field at t = 0. The value of induced emf in the loop at t = 10 s will be :

A thin stiff insulated metal wire is bent into a circular loop with its two ends extending tangentially from the same point of the loop. The wire loop has mass $ m $ and radius $ r $ and is in a uniform vertical magnetic field $ B_0 $. When a current $ I $ is passed through the loop, the loop turns about the line PQ by an angle $ \theta $. The angle $ \theta $ is given by:

A thin stiff insulated metal wire is bent into a circular loop with its two endsRead more on Sarthaks.com - https://www.sarthaks.com/3648985/thin-stiff-insulated-metal-circular-with-ends-extending-tangentially-from-same-point-loop

If the electric field and the magnetic field are equal in magnitude and perpendicular to each other, then:

A positive, singly ionized atom of mass number $ A_M $ is accelerated from rest by the voltage $ 192 \, \text{V} $. Thereafter, it enters a rectangular region of width $ w $ with magnetic field $ \vec{B}_0 = 0.1\hat{k} \, \text{T} $. The ion finally hits a detector at the distance $ x $ below its starting trajectory. Which of the following option(s) is(are) correct?
$ \text{(Given: Mass of neutron/proton = } \frac{5}{3} \times 10^{-27} \, \text{kg, charge of the electron = } 1.6 \times 10^{-19} \, \text{C).} $

Show that the circumference of the orbit of an electron revolving in the $ n $-th orbit is equal to $ n\lambda $ with the help of Bohr's quantum theory. Also, show the emission and absorption spectral lines between energy levels $ n = 1 $ and $ n = 3 $ of hydrogen atom.

What are electromagnetic waves? Explain two characteristics of these waves.

A charge $ Q $ is distributed over two concentric hollow spheres of radii $ r $ and $ R $ ($ R>r $) such that their surface charge densities are equal. Find the electric potential at their common center.

What is the main difference between paramagnetic and ferromagnetic substances?

If the radius of the nucleus of $^{13} \text{Al}^{27}$ is 3.6 fermi, then the radius of the nucleus of $^{52} \text{Te}^{125}$ is:

The unit of magnetic field is

A thin conducting rod MN of mass 20 gm, length 25 cm, and resistance 10 Ω are held on frictionless, long, perfectly conducting vertical rails as shown in the figure. There is a uniform magnetic field 𝐵₀= 4 T directed perpendicular to the plane of the rod-rail arrangement. The rod is released from rest at time 𝑡 = 0 and it moves down along the rails. Assume air drag is negligible. Match each quantity in List-I with an appropriate value from List-II, and choose the correct option.
[Given: The acceleration due to gravity 𝑔 = 10 m s⁻² and 𝑒⁻¹ = 0.4]

List I		List II
(P)	At 𝑡 = 0.2 s, the magnitude of the induced emf in Volt	(1)	0.07
(Q)	At 𝑡 = 0.2 s, the magnitude of the magnetic force in Newton	(2)	0.14
(R)	At 𝑡 = 0.2 s, the power dissipated as heat in Watt	(3)	1.20
(S)	The magnitude of terminal velocity of the rod in m s⁻¹	(4)	0.12
		(5)	2.00

An emf of 0.08 V is induced in a metal rod of length 10 cm held normal to a uniform magnetic field of 0.4 T, when moves with a velocity of:

The statement that is NOT true about induced emf is:

An emf of 0.5 V is developed in the secondary coil, when current in primary coil changes from 5.0 A to 2.0 A in 300 milliseconds. The mutual inductance of two coils would be:

A potentiometer with a cell of 2.4 volts and internal resistance of 2 Ω maintains potential drop across the resistance wire AB of length 2 m and resistance 10 Ω. A standard cell that maintains a constant EMF of ‘V’ volt with an internal resistance of 0.2 gives a balance point at 1.6 M length of the wire. The value of EMF of the second (standard) cell(V) is:

Suppose K is open and the rod is moved with speed of 12 cms-1 in the direction. The magnitude of the induced EMF will be :

The induced EMF produced in the moving rod if the magnetic field becomes parallel to the rails instead of becoming perpendicular will be :