Electromagnetism PYQ — Page 50

A moving coil galvanometer has resistance $50 \Omega$ and it indicates full deflection at $4 mA$ current. A voltmeter is made using this galvanometer and a $5 k\Omega$ resistance. The maximum voltage, that can be measured using this voltmeter, will be close to:

When the switch $S,$ in the circuit shown, is closed, then the value of current $i$ will be: 

For the circuit shown, with ${R}_{1}=1.0 \Omega$ , ${R}_{2}=2.0 \Omega$ , ${E}_{1}=2 V$ and ${E}_{2}={E}_{3}=4 V,$ the potential difference between the points $‘a’$ and $‘b’$ is approximately ( $in V$ ): 

In the figure shown, a circuit contains two identical resistors with resistance $R=5 \Omega$ and an inductance with $L=2 mH.$ An ideal battery of $15V$ is connected in the circuit. What will be the current through the battery long after the switch is closed? 

A circular coil having $N$ turns and radius $r$ carries a current $I.$ It is held in the $XZ$ plane in a magnetic field $B\hat{i}$ . The torque on the coil due to the magnetic field is:

A magnetic compass needle oscillates $30$ times per minute at a place where the dip is $45^{\circ}$ and $40$ times per minute where the dip is $30^{\circ}$. If ${B}_{1}$ and ${B}_{2}$ are the net magnetic fields due to the earth at the two places respectively, then the ratio ${B}_{1}/{B}_{2}$ is approximately equal to

An electric dipole is formed by two equal and opposite charges $q$ with separation $d$ . The charges have same mass m. It is kept in a uniform electric field $E.$ If it is slightly rotated from its equilibrium orientation, then its angular frequency $\omega$ is:

An electric field of $1000 \mathrm{~V} / \mathrm{m}$ is applied to an electric dipole at angle of $45^{\circ}$. The value of electric dipole moment is $10^{-29} \mathrm{C} \cdot \mathrm{m} .$ What is the potential energy of the electric dipole?

The energy associated with electric field is $({U}_{E})$ and with magnetic field is $({U}_{B})$ for an electromagnetic wave in free space. Then:

One of the two identical conducting wires of length $L$ is bent in the form of a circular loop and the other one into a circular coil of $N$ identical turns. If the same current is passed in both, the ratio of the magnetic field at the centre of the loop $({B}_{L})$ to that at the centre of the coil $({B}_{C}),$ i.e. $\frac{{B}_{L}}{{B}_{C}}$ will be

A transformer consisting of $300$ turns in the primary and $150$ turns in the secondary gives output power of $2.2 kW$ . If the current in the secondary coil is $10 A$ , then the input voltage and current in the primary coil are:

A $27 \mathrm{~mW}$ laser beam has a cross-sectional area of $10 \mathrm{~mm}^{2}$. The magnitude of the maximum electric field in this electromagnetic wave is given by: [Given permittivity of space $\epsilon_{0}=9 \times 10^{-12} \mathrm{SI}$ units, Speed of light $\left.\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}\right]$

A copper wire is wound on a wooden frame, whose shape is that of an equilateral triangle. If the linear dimension of each side of the frame is increased by a factor of $3,$ keeping the number of turns of the coil per unit length of the frame the same, then the self inductance of the coil:

A parallel plate capacitor is of area $6 c{m}^{2}$ and a separation $3 mm.$ The gap is filled with three dielectric materials of equal thickness (see figure) with dielectric constant ${K}_{1}=10, {K}_{2}=12$ and ${K}_{3}=14.$ The dielectric constant of a material which when fully inserted in above capacitor, gives same capacitance would be: 

There are two long co-axial solenoids of same length $l$. The inner and outer coils have radii $r_{1}$ and $r_{2}$ and number of turns per unit length $\mathrm{n}_{1}$ and $\mathrm{n}_{2}$, respectively. The ratio of mutual inductance to the self-inductance of the inner-coil is :

The magnetic field of a plane electromagnetic wave is given by $\vec{B}={B}_{0}\hat{i}[cos(kz-\omega t)]+{B}_{1}\hat{j}cos(kz+\omega t)$, where ${B}_{0}=3\times {10}^{–5} T$ and ${B}_{1}=2\times {10}^{–6} T$. The $\mathrm{RMS}$ value of the force experienced by a stationary charge $Q={10}^{–4} C$ at $z=0$ is closest to

In a conductor, if the number of conduction electrons per unit volume is $8.5\times {10}^{28} {m}^{-3}$ and mean free time is $25 fs$ (femto second), it’s approximate resistivity is: $({m}_{e}=9.1\times {10}^{-31} kg)$

A proton, an electron, and a Helium nucleus, have the same energy. They are in circular orbits in a plane due to magnetic field perpendicular to the plane. Let ${r}_{p},{r}_{e}$ and ${r}_{He}$ be their respective radii, then,

In an experiment, electrons are accelerated, from rest, by applying a voltage of $500 \mathrm{~V}$. Calculate the radius of the path if a magnetic field $100 \mathrm{mT}$ is then applied. [Charge of the electron $=1.6 \times 10^{-19} \mathrm{C}$ Mass of the electron $\left.=9.1 \times 10^{-31} \mathrm{~kg}\right]$

A solid conducting sphere, having a charge $Q,$ is surrounded by an uncharged conducting hollow spherical shell. Let the potential difference between the surface of the solid sphere and that of the outer surface of the hollow shell be $V.$ If the shell is now given a charge of $–4Q,$ the new potential difference between the same two surfaces is:

A circuit connected to an ac source of emf $e={e}_{0}\mathrm{sin}⁡(100t)$ with $t$ in seconds, gives a phase difference of $\frac{\pi }{4}$ between the emf $e$ and current $i$ . Which of the following circuits will exhibit this?

A positive point charge is released from rest at a distance ${r}_{0}$ from a positive line charge with uniform charge density. The speed $(v)$ of the point charge, as a function of instantaneous distance $r$ from line charge, is proportional to 

A plane electromagnetic wave having a frequency $f=23.9 GHz$ propagates along the positive $z-$ direction in free space. The peak value of the Electric Field is $60 V/m.$ Which among the following is the acceptable magnetic field component in the electromagnetic wave?

A bar magnet is demagnetized by inserting it inside a solenoid of length $0.2 m, 100$ turns, and carrying a current of $5.2 A.$ The coercivity of the bar magnet is: