Electromagnetism PYQ — Page 56

A monochromatic beam of light has a frequency $v=\frac{3}{2\pi }\times {10}^{12}$ $\mathrm{Hz}$ and is propagating along the direction $\frac{\hat{i}+\hat{j} }{\sqrt{2}}$ . It is polarized along the $\hat{k}$ direction. The acceptance form the magnetic field is:

A heating element has a resistance of $100 \Omega$ at room temperature. When it is connected to a supply of $220V$, a steady current of $2A$ passes in it and temperature is $500{}^{o}C$ more than the room temperature. The temperature coefficient of resistance of the heating element is

[12] A solid ball of radius $\mathrm{R}$ has a charge density $\rho$ given by $\rho=\rho_0\left(1-\frac{r}{R}\right)$ for $0 \leq r \leq R$. The electric field outside the ball is:

In the given circuit all resistances are of value $R$ ohm each. The equivalent resistance between $A$ and $B$ is: 

The $B-H$ curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with $1000\mathrm{turns}{\mathrm{cm}}^{-1}$. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is, 

The equivalent capacitance between $A$ and $B$ in the circuit is given below. 

A body of mass $M$ and charge $q$ is connected to a spring of spring constant $k$. It is oscillating along $\mathrm{x}$-direction about its equilibrium position, taken to be at $x=0$, with an amplitude $A$. An electric field $E$ is applied along the $\mathrm{x}$-direction. Which of the following statements is correct?

An electron, a proton and an alpha particle having the same kinetic energy are moving in circular orbits of radii ${r}_{e}, {r}_{p}, {r}_{\alpha }$ respectively in a uniform magnetic field B. The relation between ${r}_{e}, {r}_{p}, {r}_{\alpha }$ is:

An EM wave from air enters a medium. The electric fields are ${\vec{E}}_{1}={E}_{01}\hat{x}\mathrm{cos}⁡[2\pi v(\frac{z}{c}-t)]$ in air and ${\vec{E}}_{2}={E}_{02}\hat{x}\mathrm{cos}⁡[k(2z-ct)]$in medium, where the wave number k and frequency $v$ refer to their values in the air. The medium is non-magnetic. If ${\epsilon }_{{r}_{1}}$ and ${\epsilon }_{{r}_{2}}$ refer to relative permittivities of air and medium respectively, which of the following options, is correct?

A parallel plate capacitor with area $200 \mathrm{~cm}^2$ and separation between the plates $1.5 \mathrm{~cm}$, is connected across a battery of emf V. If the force of attraction between the plates is $25 \times 10^{-6} \mathrm{~N}$, the value of $V$ is approximately: $$ \left.\left(\varepsilon_0=8.85 \times 10^{-12} \frac{\mathrm{C}^2}{\text { N.m }}\right)^2\right) $$

In a meter bridge, as shown in the figure, it is given that resistance $Y=12.5 \Omega$ and that the balance is obtained at a distance $39.5 \mathrm{~cm}$ from end $A$ (by jockey J). After interchanging the resistances $X$ and $Y$, a new balance point is found at a distance $l_2$ from end $A$. What are the values of $X$ and $l_2$ ? 

A plane electromagnetic wave of wavelength $\lambda$ has an intensity $I$. It is propagating along the positive $Y-$direction. The allowed expressions for the electric and magnetic fields are given by:

In the following circuit the switch $S$is closed at $t=0$. The charge on the capacitor ${C}_{1}$ as a function of time will be given by $({C}_{eq}= \frac{{C}_{1}{C}_{2}}{{C}_{1}+ {C}_{2}})$ 

A capacitor $\mathrm{C}_1$ is charged up to a voltage $\mathrm{V}=$ $60 \mathrm{~V}$ by connecting it to battery $\mathrm{B}$ through switch (1), Now $\mathrm{C}_1$ is disconnected from battery and connected to a circuit consisting of two uncharged capacitors $\mathrm{C}_2=3.0 \mu \mathrm{F}$ and $\mathrm{C}_3=6.0 \mu \mathrm{F}$ through a switch $(2)$ as shown in the figure. The sum of final charges on $\mathrm{C}_2$ and $\mathrm{C}_3$ is: 

The equivalent capacitance between $A$ and $B$ in the circuit given below is: 

A constant voltage is applied between two ends of a metallic wire. If the length is halved and the radius of the wire is doubled, the rate of heat developed in the wire will be:

A galvanometer with its coil resistance $25 \Omega$ requires a current of $1\mathrm{mA}$ for its full deflection. In order to construct an ammeter to read up to a current of $2A$ the approximate value of the shunt resistance should be:

In an $\text{A.C.}$ circuit, the instantaneous e.m.f. and current are given by, $E=100\mathrm{sin}30t$$,I=20\mathrm{sin}(30t-\frac{\pi }{4})$. In one cycle of $\text{A.C.}$, the average power consumed by the circuit (in watt) and the watt-less current (in ampere) are, respectively:

In a circuit for finding the resistance of a galvanometer by half deflection method, a $6V$ battery and a high resistance of $11 k\Omega$ are used. The figure of merit of the galvanometer is $60 \mu A{\mathrm{division}}^{-1}$. In the absence of shunt resistance, the galvanometer produces a deflection of $\theta =9$ divisions when current flows in the circuit. The value of the shunt resistance that can cause the deflection of $\frac{\theta }{2}$, is closest to:

In the given circuit all resistance is of the value of $R$ ohm each. The equivalent resistance between $A$ and $B$ is: 

A coil of cross-sectional area $A$ having $n$ turns is placed in a uniform magnetic field $B$. When it is rotated with an angular velocity $\omega ,$ the maximum e.m.f. induced in the coil will be:

Three concentric metal shells $A,B$ and $C$ of respective radii $a,b$ and $c(a<b<c)$ have surface charge densities $+\sigma ,-\sigma$ and $+\sigma$ respectively. The potential of shell $B$ is:

A copper rod of mass $\mathrm{m}$ slides under gravity on two smooth parallel rails, with separation $l$ and set at an angle of $\theta$ with the horizontal. At the bottom, rails are joined by a resistance R. There is a uniform magnetic field $\mathrm{B}$ normal to the plane of the rails, as shown in the figure. The terminal speed of the copper rod is: 

Two identical conducting spheres $A$ and $B$ carry an equal charges. They are separated by a distance much larger than their diameters, and the force between them is $F$. A third identical conducting sphere, $C$, is uncharged. Sphere $C$ is first touched to $A$, then to $B$, and then removed. As a result, the force between $A$ and $B$ would be equal to: