Electromagnetism PYQ — Page 28

Two isolated metallic solid spheres of radii $R$ and $2R$ are charged such that both have same charge density $\sigma$ . The spheres are then connected by a thin conducting wire. If the new charge density of the bigger sphere is ${\sigma }^{'}$. The ratio $\frac{{\sigma }^{'}}{\sigma }$ is :

As shown in the figure, a network of resistors is connected to a battery of $24V$ with an internal resistance of $3\Omega$. The currents through the resistors ${R}_{4}$ and ${R}_{5}$ are ${I}_{4}$ and ${I}_{5}$ respectively. The values of ${I}_{4}$ and ${I}_{5}$ are: 

Three concentric spherical metallic shells $X,Y$ and $Z$ of radius $a,b$ and $c$ respectively $[a<b<c]$ have surface charge densities $\sigma ,–\sigma$ and $\sigma$, respectively. The shells $X$ and $Z$ are at same potential. If the radii of $X&Y$ are $2\mathrm{cm}$ and $3\mathrm{cm}$, respectively. The radius of shell $Z$ is _____$\mathrm{cm}$.

Two identical cells each of emf $1.5V$ are connected in series across a $10\Omega$ resistance. An ideal voltmeter connected across $10\Omega$ resistance reads $1.5V$. The internal resistance of each cell is _____ $\Omega$.

An emf of $0.08V$ is induced in a metal rod of length $10\mathrm{cm}$ held normal to a uniform magnetic field of $0.4T$, when move with a velocity of:

Expression for an electric field is given by $\vec{E}=4000{x}^{2}\hat{i}V{m}^{-1}$. The electric flux through the cube of side $20\mathrm{cm}$ when placed in electric field (as shown in the figure) is ______ $V\mathrm{cm}$. 

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by $50%$. The percentage change in voltage sensitivity of the galvanometer will be :

Considering a group of positive charges, which of the following statements is correct?

All electromagnetic wave is transporting energy in the negative $z$ direction. At a certain point and certain time the direction of electric field of the wave is along positive $y$ direction. What will be the direction of the magnetic field of the wave at that point and instant?

In the given circuit the value of $|\frac{{I}_{1}+{I}_{3}}{{I}_{2}}|$ is: 

A square loop of area $25{\mathrm{cm}}^{2}$ has a resistance of $10\Omega$. The loop is placed in uniform magnetic field of magnitude $40.0T$. The plane of loop is perpendicular to the magnetic field. The work done in pulling the loop out of the magnetic field slowly and uniformly in $1.0$ sec, will be

In the following circuit, the magnitude of current ${I}_{1}$, is ______ $A$. 

The amplitude of magnetic field in an electromagnetic wave propagating along $y$-axis is $6.0\times {10}^{–7}T$. The maximum value of electric field in the electromagnetic wave is

A $12V$ battery connected to a coil of resistance $6Ω$ through a switch, drives a constant current in the circuit. The switch is opened in $1\mathrm{ms}$. The emf induced across the coil is $20V$. The inductance of the coil is :

An electron is allowed to move with constant velocity along the axis of current carrying straight solenoid. (A) The electron will experience magnetic force along the axis of the solenoid. (B) The electron will not experience magnetic force. (C) The electron will continue to move along the axis of the solenoid. (D) The electron will be accelerated along the axis of the solenoid. (E) The electron will follow parabolic path-inside the solenoid. Choose the correct answer from the option given below:

A transformer operating at primary voltage $8\mathrm{kV}$ and secondary voltage $160V$ serves a load of $80\mathrm{kW}$. Assuming the transformer to be ideal with purely resistive load and working on unity power factor, the loads in the primary and secondary circuit would be

The magnetic field at a distance r from a long straight wire carrying current I is:

A capacitor of capacitance $500\mu F$ is charged completely using a de supply of $100V$. It is now connected to an inductor of inductance $50\mathrm{mH}$ to form an LC circuit. The maximum current in LC circuit will be _____ $A$.

A closely wounded circular coil of radius $5\mathrm{cm}$ produces a magnetic field of $37.68\times {10}^{-4}T$ at its center. The current through the coil is _____ $A$. [Given, number of turns in the coil is $100$ and $\pi =3.14$]

${B}_{X}$ and ${B}_{Y}$ are the magnetic field at the centre of two coils of two coils $X$ and $Y$ respectively, each carrying equal current. If coil $X$ has $200$ turns and $20\mathrm{cm}$ radius and coil $Y$ has $400$ turns and $20\mathrm{cm}$ radius, the ratio of ${B}_{X}$ and ${B}_{Y}$ is

Given below are two statements : Statement $I$: The electric force changes the speed of the charged particle and hence changes its kinetic energy; whereas the magnetic force does not change the kinetic energy of the charged particle. Statement $\mathrm{II}$: The electric force accelerates the positively charged particle perpendicular to the direction of electric field. The magnetic force accelerates the moving charged particle along the direction of magnetic field. In the light of the above statements, choose the most appropriate answer from the options given below :

In the given figure, the value of ${V}_{0}$ will be _____ $V$. 

A conducting circular loop is placed in $X-Y$ plane in presence of magnetic field $\vec{B}=(3{t}^{3}\hat{j}+3{t}^{2}\hat{k})$ in SI unit. If the radius of the loop is $1m$, the induced emf in the loop, at time, $t=2s$ is $n\pi V$. The value of $n$ is _____ .

Sun light falls normally on a surface of area $36{\mathrm{cm}}^{2}$ and exerts an average force of $7.2\times {10}^{-9}N$ within a time period of $20$ minutes. Considering a case of complete absorption, the energy flux of incident light is