Electromagnetism PYQ — Page 18

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). 

In series LCR circuit, the capacitance is changed from $C$ to $4C$. To keep the resonance frequency unchanged, the new inductance should be :

A transformer has an efficiency of $80%$ and works at $10V$ and $4\mathrm{kW}.$ If the secondary voltage is $240V,$ then the current in the secondary coil is:

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

In an electrical circuit drawn below the amount of charge stored in the capacitor is _______ $\mu C.$ 

Paramagnetic substances: A. align themselves along the directions of external magnetic field. B. attract strongly towards external magnetic field. C. has susceptibility little more than zero. D. move from a region of strong magnetic field to weak magnetic field. Choose the most appropriate answer from the options given below:

A potential divider circuit is shown in figure. The output voltage ${V}_{0}$ is 

A regular polygon of $6$ sides is formed by bending a wire of length $4\pi$ meter. If an electric current of $4\pi \sqrt{3}A$ is flowing through the sides of the polygon, the magnetic field at the centre of the polygon would be $x\times {10}^{-7}T.$ The value of $x$ is ______.

In an a.c. circuit, voltage and current are given by: $V=100\mathrm{sin}(100t)V$ and $I=100\mathrm{sin}(100t+\frac{\pi }{3})\mathrm{mA}$ respectively. The average power dissipated in one cycle is :

Two identical capacitors have same capacitance $C$. One of them is charged to the potential $V$ and other to the potential $2V$. The negative ends of both are connected together. When the positive ends are also joined together, the decrease in energy of the combined system is :

An alternating voltage of amplitude $40 \mathrm{~V}$ and frequency $4 \mathrm{kHz}$ is applied directly across the capacitor of $12 \mu \mathrm{F}$. The maximum displacement current between the plates of the capacitor is nearly :

A straight magnetic strip has a magnetic moment of $44 \mathrm{Am}^2$. If the strip is bent in a semicircular shape, its magnetic moment will be _______ $\mathrm{Am}^2$. (given $\pi=\frac{22}{7}$ )

A galvanometer having coil resistance $10\Omega$ shows a full scale deflection for a current of $3\mathrm{mA}$. For it to measure a current of $8A$, the value of the shunt should be:

In the given figure, the charge stored in $6\mu F$ capacitor, when points $A$ and $B$ are joined by a connecting wire is _______$\mu C$. 

An electric bulb rated $50 \mathrm{~W}-200 \mathrm{~V}$ is connected across a $100 \mathrm{~V}$ supply. The power dissipation of the bulb is:

In the given figure an ammeter A consists of a $240 \Omega$ coil connected in parallel to a $10 \Omega$ shunt. The reading of the ammeter is $\qquad$ $\mathrm{mA}$ 

In an ammeter, $5%$ of the main current passes through the galvanometer. If resistance of the galvanometer is $G,$ the resistance of ammeter will be:

Match List I with List II  Chose the correct answer from the options given below

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason(R) Assertion (A) : Work done by electric field on moving a positive charge on an equipotential surface is always zero. Reason (R) : Electric lines of forces are always perpendicular to equipotential surfaces. In the light of the above statements, choose the most appropriate answer from the options given below :

A galvanmeter has a coil of resistance $200 \Omega$ with a full scale deflection at $20 \mu \mathrm{A}$. The value of resistance to be added to use it as an ammeter of range $(0-20) \mathrm{mA}$ is ;

A wire of length $10\mathrm{cm}$ and radius $\sqrt{7}\times {10}^{-4}m$ connected across the right gap of a meter bridge. When a resistance of $4.5\Omega$ is connected on the left gap by using a resistance box, the balance length is found to be at $60\mathrm{cm}$ from the left end. If the resistivity of the wire is $R\times {10}^{-7}\Omega m$, then value of $R$ is :

Twelve wires each having resistance $2 \Omega$ are joined to form a cube. A battery of $6 \mathrm{~V}$ emf is joined across point $a$ and $c$. The voltage difference between $e$ and $f$ is ______V. 

A wire of resistance $20 \Omega$ is divided into 10 equal parts, resulting pairs. A combination of two parts are connected in parallel and so on. Now resulting pairs of parallel combination are connected in series. The equivalent resistance of final combination is _____ $\Omega$.

Two identical conducting spheres $P$ and $S$ with charge $Q$ on each, repel each other with a force $16 \mathrm{~N}$. A third identical uncharged conducting sphere $R$ is successively brought in contact with the two spheres. The new force of repulsion between $\mathrm{P}$ and $\mathrm{S}$ is :