When two capacitors charged to different potentials are connected by a conducting wire, what is not true?

A circular current loop of magnetic moment M is in arbitrary orientation in an external magnetic field. \(\overset { \rightarrow }{ B } \) The work does to rotate the loop by \(30°\) about an axis perpendicular to its plane is

Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?

In an electromagnetic wave, electric and magnetic fields are 200 V/m and 0.365 A/m. The maximum rate of energy flow is 

How much work is done in moving a 500\(\mu C\) charge between two points on an equipotential surface?

In a metre bridge, the length of the wire is 100 cm. At what position will the balance point be obtained if the two resistances are in the ratio 1 : 3?

State the principle of moving coil galvanometer.

Can we control direct current without much loss of energy? Can a choke coil do so?

A charge q is placed at the centre of the line joining two equal charges Q.Show that the system of the three charges will be in equilibrium if q=-Q/4.

What is the effect of temperature on relaxation time in a metal?

A current of one ampere is passed through a straight wire of length 2.0 metre. Find the magnetic field at a point in air at a distance 3 metre from one end of wire but lying on the axis of the wire.

An alternating voltage of frequency f is applied across a series LCR circuit. Let f_r be the resonance frequency for the circuit. Will the current in the circuit lag, lead or remain in phase with the applied voltage when (i) f > f_r (ii) f < f_r ? Explain your answer in each case.

Considering the case of a parallel plate capacitor being charged, show how one is required to generalize Ampere's circuital law to include the term due to displacement current.

When 1 x 10¹² electrons are transferred from one conductor to another, a potential difference of 10 V appears between the conductors. Find the capacitance of the two conductors.

What is the advantages of using thick metallic strips to join wires in a potentiometer?

Define the term magnetic permeability of a magnetic material. Write any two characteristics of a magnetic substance if it is to be used to make a permanent magnet. Give an example of such a material.

A loop, made of straight edges has six corners at A (0, 0, 0), B (L, 0, 0), C (L, L, 0), D(0, L, 0), E (0, L, L) and F (0, 0, L). A magnetic field \(B={ B }_{ 0 }\left( \hat { i } +\hat { k } \right) T\) is present in the region. The flux passing through the loop ABCDEFA (in that order) is.
(a) \({ B }_{ 0 }{ L }^{ 2 }Wb\)
(b) \(2{ B }_{ 0 }{ L }^{ 2 }Wb\)
(c) \(\sqrt { 2 } { B }_{ 0 }{ L }^{ 2 }Wb\)
(d) \(4{ B }_{ 0 }{ L }^{ 2 }Wb.\)

(a) Define electric flux. Write its S.I. unit.
(b) Using Gauss's law, prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance from it.
(c) How is the field directed if
(i) the sheet is positively charged,
(ii) negatively charged?

Based on the previous knowledge learnt in the class, two students of class XII (A and B) were asked to conduct an experiment in the laboratory using a meter bridge one made of Nichrome and the other one made of Copper, of same length and same diameter, of constant potential difference. The student A could not give explanation for not achieving the result whereas student B, could get the result and was also able to explain.
(a) What made student B to perform successfully?
(b) Give the formula to calculate the rate of heat production.

Define magnetic dipole and dipole moment.What are its units?

(i) Define mutual inductance and write its SI units.
(ii) Derive an expression for the mutual inducyance of two long coaxial solenoids of same lengt wound one over the other.
(iii) In an experiment, two coils C₁ and C₂ are placed close to each other. Find out the expression for the emf induced in the coil C₁ due to a change in the current through the coil C₂.

Draw a labelled diagram of a step-down transformer. State the principle of its working.
Express the turn ratio in terms of voltages.
Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer.
How much current is drawn by the primary of a transformer Connected to 220 V supply when it delivers power to a 110 V-550 W refrigerator?

At what temperature a hot body will emit an e.m. wave of wavelength \(1\mu m\) ?

It is required to construct a \(10\mu F\) capacitor which can be connected across a 200 V battery. Capacitors of capacitance \(10\mu F\) are available but they can with stand only 50V. Design a combination which can yield the desired result.

With switch S open the network of resistors shown here drawn a current I from the battery. How many times will this current become on closing the switch S?

A resistance of 1980 \(\Omega \) is connected in series with a voltmeter, after which the scale division becomes 100 times larger. Find the resistance of voltmeter.

A 60 V-10 W electric lamp is to be run on 100 V-60Hz mains. Calculate the inductance of the choke coil to achieve the same result, calculate its value.

A resistor of 200 ohm and a capacitor of 15.0 \(\mu\) F are connected in series to a 220V, 50Hz a.c. source.
(a) Calculate the current in the circuit
(b) Calculate the r.m.s. voltage across the resistor and the capacitor. Is the algebraic sum of these voltages more than the source voltage? If yes, resolve the paradox.

How would you establish an instantaneous displacement current of 2.0 A in the space between the two parallel plates of \(1\mu F\) capacitor?

A plane electromagnetic wave of frequency 25 MHz travels in free space along the x-direction. At a particular point in space and time, \( { E } =6.3 \hat { j } \)V/m. What is B at this point?