The magnetic field at a perpendicular distance of 2 cm from an infinite straight current carrying conductor is 2x10^-6 T. The current in the wire is

A positive charge is moving towards an observer. The direction of magnetic induction lines is 

If a copper wire carries a direct current, the magnetic field associated with the current will be

A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through \({ 60 }^{ ° }.\) The torque required to keep the needle in this position will be 

The work done in turning a magnet of magnetic moment M by an angle of \({ 90 }^{ ° }\) from the magnetic meridian is n times the corresponding work done to turn it through an angle of \({ 60 }^{ ° },\) where n is

How can you keep a constant current inside a conductor?

A 4 \(\Omega\) non-insulated resistance wire is bent in the middle by 180^o and both the halves are twisted with each other. What will be its new resistance?

Two wires of equal length one of copper and other of manganin have the same resistance. Which wire is thicker?

It is easier to start a car engine on a warm day than on a chilly day. Why?

What is the order of magnitude of the resistance of a (dry) human body?

Currents of the order of 0.1 A through the human body are fatal. What causes the death: heating of the body due to electric current or something else?

While making a standard resistance, the coil is made of manganin. The coil is double folded and is wound over a non-conducting frame. Why? 

Define the units of conductance and conductivity. Give their dimensional formulae.

Thermistors differ from ordinary resistors. Explain.

What are superconductors? Write their two applications.

Three identical resistors, each of resistance R, when connected in series with a d.c. source, dissipate power X. If the resistors are connected in parallel to the same d.c. source, how much power will be dissipated?

Use Kirchhoff,s rules to determine the value of the current I₁ flowing in the circuit shown in the figure.
           

In the given circuit, assuming point A to be at zero potential, use Kirchhoff,s rules to determine the potential at point B.

AB is a potentiometer wire as shown in figure. If the value of R is increased, in which direction will the balance point J shift?

Distinguish between emf (\(\varepsilon \)) and terminal voltage (V) of a cell having internal resistance 'r'. Draw a plot showing the variation of terminal voltage (V) vs the current (I) drawn from the cell. Using this plot, how does one determine the internal resistance of the cell?

Figure shows a potentiometer with a cell of 2.0V and internal resistance of 0.40\(\Omega\) maintaining a potential drop across the resistor wire AB. A standard cell which maintains a constant emf of 1.02V (for very moderate currents upto a few mA) gives a balance point at 67.3 cm length of the wire. To ensure very low currents drawn from the standard cell a very high resistance 600k\(\Omega\) is put in series with it Which is shorted cell is then replaced by a cell of unknown emf E and the balance point found similarly, turns out to be at 82.3 cm length of the wire.

(a) What is the value E?
(b) What purpose does the high resistance o 600k\(\Omega\) have?
(c) Is the balance point affected by this high resistance?
(d) Is the balance point affected by the internal resistance of 600k\(\Omega\) have?
(e) Would the method work in the above situation if the driver cell of the potentiometer had an emf of 1.0V instead of 2.V?
(f) Would the circuit work well for determining an etremely small emf say of the order of a few mV (such as the typical emf of a thermo-couple)? If not how will you modiy the circuit?

A dc supply of 120V  is connected to a large resistance X. A voltmeter of resistance 10k\(\Omega\)placed in series in the circuit reads 4V. What is the value of X? What so you think is the purpose in using a voltmeter instead of an ammeter to determine the large resistance X?

A heating element using nichrome connected to a 230 V supply draws an initial current of 3.2 A which settles after a few seconds to a steady value of 2.8 A. What is the steady temperature of the heating element if the room temperature is \({ 27.0 }^{ \circ }C\)? Temperature coefficient of resistance of nichrome averaged over the temperature range involved is \(1.70\times { 10 }^{ -4\circ }{ C }^{ -1 }\)?

What conclusion can you draw from the following observations on a resistor made of alloy manganin:

Two cells of voltages 10V and 2V and internal resistances \(10\Omega\ and\ 5\Omega \) respectively are connected in parallel with the positive end of 10V battery connected to negative pole of 2V battery. Find the effective voltage and effective resistance of the combination.

That night Vaikunth was preparing for his physics exam. Suddenly, the light in his room went off and he could not continue his studies. His cousin brother Vasu who had come to visit him was quick to react. Vasu using the torch (an android application) installed in his mobile phone found that the fuse had blown out. He checked the wiring and located a short circuit. He checked the wiring and located a short circuit. He rectified it and put a fuse wire. The light came to life again. Vaikunth had a sign of releif and continued his studies.
Read the above passage and answer the following question.
(i) What are the values projected by Vaikunth and Vasu?
(ii) Why did Vasu have to check the wiring?
(iii) What is an electric fuse? What characteristics you would prefer for a fuse wire?

The unknown resistance of a conductor can be determined by Wheatstone bridge. The standard form of Wheatstone bridge is shown in the figure. It can be shown when the bridge is balanced.

\(\frac { P }{ Q } =\frac { R }{ S } \quad or\quad S=\frac { Q }{ P } R\)
Knowing P,Q and R, unknown resistance S can be calculated.
Read the above passage and answer the following questions.
(i) Name any two applications of Wheatstone bridge.
(ii) What is the practical utility of the post office box in day to day life?

Kumaran wanted to pay electricity bill that day. He realized that the consumption shown by the meter was unbelievably low. He thought that the -meter must have been faulty. He wanted to check the meter. But unfortunately, he did not have any idea as to how to do this. There came his friend Subhash to help him. He told Kumaran to run only the electric heater rated 1kW in his house for some time keeping other appliances switched off. He also calculated the power consumed in kilowatt hour and compared the value with the meter.  Kumaran as happy and thanked Subhash for his timely help and the knowledge.
(1) What are the values displayed by the friends?
(2) Express kWh in joules. Find the resistance of the heater.

Rajesh has an old two wheeler. One day he wanted to start his two wheeler but he could not do so. He observed carefully and found that its battery was defective. Then he arranged 6 V dry cell battery but it was also unable to start two wheeler. Then his friend Mahesh came and suggested him that this battery will not work because its internal resistance is more and it cannot give a desired current of 30 A which is required for starting the two wheelers. As per his suggestion, Rajesh got fitted a lead acid battery of 6 V and his problem was solved.
(a) According to you, what values were displayed by Mahesh?
(b) The storage battery of a car has an emf 12 V. If the internal resistance of the battery is 0.4 Ω, what is the maximum current that can be drawn from the battery?

You are given a 8 \(\Omega\) resistor. What length of constant wire of resistance 120\(\Omega\) m^-1 should be joined in parallel with it to get a value of 6\(\Omega\)?

Two nichrome wires are connected in series with a battery. The length of nichrome wires are in the ratio of 1:2 whereas their resistance are in the ratio 2:1. Find the following 
(a) ratio of their diameters
(b) ratio of drift velocity of free electrons in them.

Storage battery of a car has an e.m.f of 12V. If the internal resistance of the battery is 0.4\(\Omega\) What is the maximum current that can be drawn from the battery?

A rectangular coil of area 5.0 x 10^-4 m² and 60 turns is pivoted about one of its vertical sides. The coil is in a radial horizontal field of 90 G (radial here means the field lines are in the plane of the coil for any rotation). What is the torsional constant of the hair springs connected to the coil, if a current of 2.0 mA produces an angular deflection of 18^o?

The current sensitivity of a moving coil galvanometer increases by 20% when its resistance is increased by a factor does the voltage sensitivity change ?