Electromagnetism PYQ — Page 20

A coil in the shape of an equilateral triangle of side $l$ is suspended between the pole of a permanent magnet such that $B$ is in plane of the coil. If due to current $i$ in the triangle a torque $\tau$ acts on it, the side $l$ of the triangle is:

Two batteries, one of emf 18 volts and internal resistance $2 \Omega$ and the other of emf 12 volts and internal resistance $1 \Omega$, are connected as shown. The voltmeter $V$ will record a reading of: 

As a result of change in the magnetic flux linked to the closed loop as shown in the figure, an e.m.f. $V$ volt is induced in the loop. The work done (joules) in taking a charge $Q$ coulomb once along the loop is: 

If $\lambda_v, \lambda_x$ and $\lambda_m$ represent the wavelength of visible light, X-rays and microwaves respectively, then:

In a circuit $\mathrm{L}, \mathrm{C}$ and $\mathrm{R}$ are connected in series with an alternating voltage source of frequency $f$. The current leads the voltage by $45^{\circ}$. The value of $\mathrm{C}$ is:

An electron moves in a circular orbit with a uniform speed $v$. It produces a magnetic field $B$ at the centre of the circle. The radius of the circle is proportional to:

Two charge $q_1$ and $q_2$ are placed $30 \mathrm{~cm}$ apart, as shown in the figure. A third charge $q_3$ is moved along the are of a circle of radius $40 \mathrm{~cm}$ from $\mathrm{C}$ to $\mathrm{D}$. The change in the potential energy of the system is \(\frac{q_3 k}{4 \pi \in_0}\), where $k$ is: 

A network of four capacitors capacity equal $C_1=C, C_2=2 C, C_3=3 C$ and $C_4=$ $4 C$ are conducted to a battery as shown in the figure. The ratio of the change on $C_2$ and $C_4$ is: 

The electric resistance of a certain wire of iron is $R$. If its length and radius are both doubled, then:

A 6 volt battery is connected to the terminal of a three metre long wire of uniform thickness and resistance of 100 $\mathrm{ohm}$. The difference of potential between two points on the wire separated by a distance of $50 \mathrm{~cm}$ will be:

A coil of 40 henry inductance is connected in series with a resistance of $8 \mathrm{ohm}$ and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is:

Five equal resistance each of resistance $R$ are connected as shown in the figure. A battery of $V$ volts is connected between $\mathrm{A}$ and $\mathrm{B}$. The current flowing in AFCEF will be: 

Resistance $n$, each of $r$ ohm, when connected in parallel give an equivalent resistance $R \mathrm{~ohm}$. If these resistances were connected in series, the combination would have a resistance in ohms, equal to :

A battery is charged at a potential of 15 $\mathrm{V}$ for 8 hours when the current flowing is $10 \mathrm{~A}$. The battery on discharge supplies a current of $5 \mathrm{~A}$ for 15 hours. The mean terminal voltage during discharge is $14 \mathrm{~V}$. The "Watt-hour" efficiency of the battery is:

In India electricity is supplied for domestic use at $220 \mathrm{~V}$. It is supplied at $110 \mathrm{~V}$ in USA. If the resistance of a $60 \mathrm{~W}$ bulb for use in India is $R$, the resistance of a $60 \mathrm{~W}$ bulb for use in USA will be:

A bullet of mass $2 \mathrm{~g}$ is having of $2 \mu \mathrm{C}$. Through what potential difference must it be accelerated, starting from rest, to acquire a speed of of $10 \mathrm{~m} / \mathrm{s}$ ?

A galvanometer acting as a voltmeter will have:

When three identical bulbs of 60 watt, 200 volt rating are connected in series to a 200 volt supply, the power drawn by them will be:

The magnetic flux through a circuit of resistance $R$ changes by an amount $\Delta \phi$ in a time $\Delta t$. Then the total quantity of electric charge $Q$ that passes any point in the circuit during the time $\Delta \mathrm{t}$ is represented by:

A galvanometer of $50 \mathrm{ohm}$ resistance has 25 divisions. A current $4 \times 10^{-4}$ ampere gives a deflection of one division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of:

A electric dipole has the magnitude of its charge as $q$ and its dipole moment is $p$. It is placed in a uniform electric field $E$. If its dipole moment is along the direction of the field, the force on it and it and its potential energy are respectively:

A diamagnetic material in a magnetic field moves:

A bar magnet is oscillating in the Earth's magnetic field with a period $T$. What happens to its period and motion if its mass is quadrupled?

An electric kettle has two heating coils. When one of the coils is connected to a.c. source, the water in the kettle boils in 10 minute. When the other coil is used the water boils in 40 minute. If both the coils are connected in parallel, the time taken by the same quantity of water to boil will be: