Electromagnetism PYQ — Page 18

Two cells are connected in opposition as shown. Cell ${E}_{1}$ is of $8V$ emf and $2\Omega$ internal resistance; the cell ${E}_{2}$ is of $2V$ emf and $4\Omega$ internal resistance. The terminal potential difference of cell ${E}_{2}$ is ______ $V$. 

The electric current through a wire varies with time as $I={I}_{0}+\beta t$, where ${I}_{0}=20A$ and $\beta =3A{s}^{-1}$. The amount of electric charge crossed through a section of the wire in $20s$ is:

A current of $200\mu A$ deflects the coil of a moving coil galvanometer through $60^{\circ}$. The current to cause deflection through $\frac{\pi }{10}$ radian is

The coercivity of a magnet is $5 \times 10^3 \mathrm{~A} / \mathrm{m}$. The amount of current required to be passed in a solenoid of length $30 \mathrm{~cm}$ and the number of turns 150 , so that the magnet gets demagnetised when inside the solenoid is _____A.

Two identical charged spheres are suspended by strings of equal lengths. The string make an angle of $37^{\circ}$ with each other. When suspended in a liquid of density $0.7g{\mathrm{cm}}^{-3}$, the angle remains same. If density of material of the sphere is $1.4g{\mathrm{cm}}^{-3}$, the dielectric constant of the liquid is _____ $(\mathrm{tan}37^{\circ}=\frac{3}{4})$

A wire of resistance $R$ and radius $r$ is stretched till its radius became $r / 2$. If new resistance of the stretched wire is $x R$, then value of $x$ is _______

The equivalent resistance between $\mathrm{A}$ and $\mathrm{B}$ is : 

Three infinitely long charged thin sheets are placed as shown in figure. The magnitude of electric field at the point $P$ is $\frac{x \sigma}{\epsilon_o}$. The value of $x$ is _______ (all quantities are measured in SI units). 

The number of electrons flowing per second in the filament of a $110 \mathrm{~W}$ bulb operating at $220 \mathrm{~V}$ is : $\left(\right.$ Given $\left.\mathrm{e}=1.6 \times 10^{-19} \mathrm{C}\right)$

Water boils in an electric kettle in 20 minutes after being switched on. Using the same main supply, the length of the heating element should be _____ to _____ times of its initial length if the water is to be boiled in 15 minutes.

Two circular coils $P$ and $Q$ of $100$ turns each have same radius of $\pi \mathrm{cm}$. The currents in $P$ and $R$ are $1A$ and $2A$ respectively. $P$ and $Q$ are placed with their planes mutually perpendicular with their centers coincide. The resultant magnetic field induction at the center of the coils is $\sqrt{x}\mathrm{mT}$, where $x=$ ______. [Use ${\mu }_{0}=4\pi \times {10}^{-7}Tm{A}^{-1}$]

An electron with kinetic energy $5 \mathrm{eV}$ enters a region of uniform magnetic field of 3 $\mu \mathrm{T}$ perpendicular to its direction. An electric field $\mathrm{E}$ is applied perpendicular to the direction of velocity and magnetic field. The value of $E$, so that electron moves along the same path, is _______ $\mathrm{NC}^{-1}$. $\left(\right.$ Given, mass of electron $=9 \times 10^{-31} \mathrm{~kg}$, electric charge $\left.=1.6 \times 10^{-19} \mathrm{C}\right)$

A plane electromagnetic wave of frequency $35\mathrm{MHz}$ travels in free space along the $X$-direction. At a particular point (in space and time) $\vec{E}=9.6\hat{j}V{m}^{-1}$. The value of magnetic field at this point is:

When a coil is connected across a $20 \mathrm{~V}$ dc supply, it draws a current of $5 \mathrm{~A}$. When it is connected across $20 \mathrm{~V}, 50 \mathrm{~Hz}$ ac supply, it draws a current of $4 \mathrm{~A}$. The self inductance of the coil is ______ $\mathrm{mH}$. $($ Take $\pi=3$ )

Given below are two statements: Statement I: Electromagnetic waves carry energy as they travel through space and this energy is equally shared by the electric and magnetic fields. Statement II: When electromagnetic waves strike a surface, a pressure is exerted on the surface. In the light of the above statements, choose the most appropriate answer from the options given below:

In the given circuit, the current flowing through the resistance $20\Omega$ is $0.3A$, while the ammeter reads $0.9A$. The value of ${R}_{1}$ is _____$\Omega$. 

The vehicles carrying inflammable fluids usually have metallic chains touching the ground :

A wire of resistance $R$ and length $L$ is cut into $5$ equal parts. If these parts are joined parallely, then resultant resistance will be :

An electron moves through a uniform magnetic field $\vec{B}={B}_{0}\hat{i}+2{B}_{0}\hat{j}T$. At a particular instant of time, the velocity of electron is $\vec{u}=3\hat{i}+5\hat{j}m{s}^{-1}$. If the magnetic force acting on electron is $\vec{F}=5e\hat{k}N$, where $e$ is the charge of electron, then the value of ${B}_{0}$ is ____ $T$.

An electric charge ${10}^{-6}\mu C$ is placed at origin $(0,0)$ $m$ of $X-Y$ co-ordinate system. Two points $P$ and $Q$ are situated at $(\sqrt{3},\sqrt{3})m$ and $(\sqrt{6},0)m$ respectively. The potential difference between the points $P$ and $Q$ will be :

A charge $q$ is placed at the center of one of the surface of a cube. The flux linked with the cube is:

To measure the internal resistance of a battery, potentiometer is used. For $\mathrm{R}=10 \Omega$, the balance point is observed at $l=500 \mathrm{~cm}$ and for $\mathrm{R}=1 \Omega$ the balance point is observed at $l=400 \mathrm{~cm}$. The internal resistance of the battery is approximately :

An ac source is connected in given series LCR circuit. The rms potential difference across the capacitor of $20 \mu \mathrm{F}$ is _____V. 

A square loop of side $10\mathrm{cm}$ and resistance $0.7\Omega$ is placed vertically in the east-west plane. A uniform magnetic field of $0.20T$ is set up across the plane in the north-east direction. The magnetic field is decreased to zero in $1s$ at a steady rate. Then, the magnitude of induced emf is $\sqrt{x}\times {10}^{-3}V$. The value of $x$ is _______.