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Recent questions tagged class 12

Derive an expression for torque acting on a electric dipole in a uniform 2 Dimensional electricfield

asked May 30, 2017 by pady_1

1 answer

characteristic of Electric Lines of Force

asked May 30, 2017 by pady_1

1 answer

Comparison of Electrostatic and Gravitational Force

asked May 30, 2017 by pady_1

1 answer

Define Coulumb’s Law

asked May 29, 2017 by pady_1

1 answer

Define Coulumb’s Law

asked May 29, 2017 by pady_1

1 answer

Define Coulumb’s Law

asked May 29, 2017 by pady_1

1 answer

Define coulomb? Force experienced by option 1 coulomb charge placed at a distance of 1 m from a similar charge is

asked May 29, 2017 by pady_1

1 answer

A magnetic field in a certain region is given by $ B = B_0 cm (\omega t) \hat {k}$ and a coil of radius "a" with resistance R is placed in the x - y plane with its centre at the origin in the magnetic field, as shown in the fig. Find the magnitude and th direction of the current at (a, 0, 0) at $ t = \frac {\pi}{2\omega} \; and \; t = \frac {3 \pi}{2 \omega}$

asked Dec 30, 2016 by suganyadevi.p

1 answer

A rectangular loop of wire ABCD is kept close to an infinitely long wire carrying a current $ I (t) = I_0 (1 - \frac {t}{T}) for $ 0 \leq t \leq T$ and $ I (0) = 0$ for t > T, as shown in the fig. Find the total charge passing through a given point in the loop, in time T, The resistance of the loop is R.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Consider an infinitely long wire carrying a current I(t), with $ \frac {dI}{dt} = \lambda = constant$. Find the current produced in the rectangular loop of wire ABCD if its resistance is R, as shown in the fig.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A magnetic field B is confined to a region $r \leq a$ and points out the paper (the Z axis) $ r = 0$ being the centre of the circular region. A charged ring (charge = Q) of radius b $b>a$ and mass m lies in the xy plane with its centre at the origin. the ring is free to rotate and is at rest. The magnetic field is brought to zero in time $\bigtriangleup t$. Find the angular velocity $\omega$ of the ring after the field vanister.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Give the expression for average value of a.c voltage $V = V_0\; sin \omega t$ over time interval $ t = 0 \; to \; t = \frac {\pi}{\omega}$

asked Dec 30, 2016 by suganyadevi.p

1 answer

An electrical element x connected to an alternating voltage source has current through it leading the voltage by $\frac {\pi}{2}$ radius. Identify x and write an expression for its reactance.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Self induction of an air core inductor increases from 0.01 MH to 10 MH on introducing an iron core into it. What is the relative permeability of the core used?

asked Dec 30, 2016 by suganyadevi.p

1 answer

The dimension of $\frac {h}{e}$ is the same as that of magnetic flux $\phi$. Say true or false.

asked Dec 30, 2016 by suganyadevi.p

1 answer

The dimensions of electric and magnetic flux are same. Say true or false.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A coil of a metal wire is kept stationary in a non - uniform magnetic field. An emf is induced in the coil. Say true or false.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A magnetic field of 10T acts normal to a coil of 50 turns having $100 cm^2$ area. Find emf induced if the coil is removed from magnetic field in 0.1 sec.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A circular copper disc 10 cm in radius rotates at $20\pi$ rad/s about an axis through its centre and perpendicular to its disc. A uniform magnetic field of 0.2T acts perpendicular to the disc. Calculate the induced current if the resistance of the disc is $2\Omega$.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A circular copper disc 10 cm in radius rotates at $20\pi$ rad/s about an axis through its centre and perpendicular to its disc. A uniform magnetic field of 0.2T acts perpendicular to the disc. Calculate the potential difference developed between the axis of the disc and the rim.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A wheel with 50 metallic spokes each 0.5 m long is rotated with an angular speed of 12 radian /sec, in a plane normal to the earth's magnetic field. If the magnitude of the field is $ 0.5 \times 10^{-4}$ T, calculate the emf induced between the axle and the rim of the wheel.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A cylindrical bar magnet is kept along the axis of a circular coil and near it as shown in the fig. Will there be any induced e.m.f at the terminals of the coil, when the magnet is related about its own axis.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of $ 50 rad s^{-1}$ in a uniform horizontal magnetic field of magnitude $ 3 \times 10^{-2} T$. Calculate the average emf.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of 50 $rad s^{-1}$ in a uniform horizontal magnetic field of magnitude $ 3 \times 10^{-2} T$. Calculate the maximum emf induced in the coil.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Write a expression for mutual inductance of two coaxial solenoids.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Why are resistance coils usually double wound?

asked Dec 30, 2016 by suganyadevi.p

1 answer

The rate of charge of magnetic flux has same units as induced e.m.f. Say true or false.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Why does a metallic piece very hot when it is surrounded by a coil carrying high frequency alternating current??

asked Dec 30, 2016 by suganyadevi.p

1 answer

A magnetic field of flux density $1.0 wb m^{-2}$ acts normal to a 80 turn coil of 0.01 m^2 area. Find the e.m.f induced in it, if this coil is removed from the field in 0.1 second.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A conducting circular loop is placed in a uniform magnetic field B = 0.020 T with its plane perpendicular to the field. The radius of the loop starts shrinking at a constant rate of 1.0 mm/s. Find the induced e.m.f in the loop at an instant when the radius is 2cm?

asked Dec 30, 2016 by suganyadevi.p

1 answer

A conducting wire of 100 turns is wound over 1cm near the centre of a solenoid of 100 cm length and 2 cm radius having 1000 turns. Calculate the coefficient of mutual inductance of the two solenoids.

asked Dec 30, 2016 by suganyadevi.p

1 answer

SI unit of magnetic flux is

asked Dec 30, 2016 by suganyadevi.p

1 answer

A wire of length 2m moves with a speed of 5 m/s perpendicular to a magnetic field of induction $0.1 wb/m^2$. The emf induced in the wire is

asked Dec 30, 2016 by suganyadevi.p

1 answer

Amount of change induced in a circuit of resistance R is given by

asked Dec 30, 2016 by suganyadevi.p

1 answer

A solenoid coil has 50 turns per cm along its length and a cross sectional area of $4cm^2$, 200 turns of another wire are wound round the first solenoid co-axially. The two coils are electrically insulated from each other. Calculate the mutual inductance between the two coils.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Two coils have mutual inductance of 1.5 henry. If current in primary circuit is raised to 5 ampere in one millisecond after closing the circuit, what is the e.m.f induced in the secondary??

asked Dec 30, 2016 by suganyadevi.p

1 answer

An e.m.f of 250 microvolt in induced in a coil when current in it changes from 10A to 6A in 0.4 second. What is the self inductance of the coil?

asked Dec 30, 2016 by suganyadevi.p

1 answer

As soon as current is switched on a high voltage line, the bird sitting on it flies away. Why??

asked Dec 30, 2016 by suganyadevi.p

1 answer

The magnetic flex through a coil perpendicular to its plane and directed into paper is varying according to the relation $\phi = (5t^2 + 10t + 5)$ milliwebers. Calculate the e.m.f induced in the loop.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A 2m long solenoid with diameter 4 cm and 2000 turns has a secondary of 1000 turns wound closely near it mid point. Calculate the mutual inductance between the two coils.

asked Dec 30, 2016 by suganyadevi.p

1 answer

An aircraft with a wingspan of 40m flies with a speed of 1080 $km hr^{-1}$ in the eastward direction at a constant altitude in the northern hemisphere where the vertical component of earth's magnetic field is $1.75 \times 10^{-5} T$. Find the emf that develops between the tips of the wings.

asked Dec 30, 2016 by suganyadevi.p

1 answer

A 12v battery connected to a $6 \Omega$, 10H coil through a switch drives a constant current in the circuit. Th switch is suddenly opened. Assuming that it took 1 millisecond to open the switch. Calculate the average e.m.f induced across the coil.

asked Dec 30, 2016 by suganyadevi.p

1 answer

Use Lenz's law to determine the direction of induced current in the situation described by figure.

A circular loop being deformed in a narrow straight wire.

asked Dec 29, 2016 by priyanka.c

1 answer

A magnetic field B = $B_{\circ} sin(\omega t)\hat{k}$ covers a large region where a wire AB slides smoothly over two parallel conductors separated by a distance d, as shown in the fig. The wires are in the x - y plane. The wire AB (of length d) has resistance R and the parallel wires have negligible resistance. If AB is moving velocity $\upsilon$, what is the current in the circuit?

asked Dec 29, 2016 by suganyadevi.p

1 answer

There are two coils A and B separated by some distance. If a current of 2A flows through A, a magnetic flex of $10^{-2}$ wb passes through B (no current through B). If no current passes through A and a current of 1A passes through B, what is the flex through A?

asked Dec 29, 2016 by suganyadevi.p

1 answer

A (current vs time) graph of the current passing through a solenoid is shown in the fig. For which time is the back electromotive force (u) a maximum? If the back emf at t = 3s is e, find the emf at t = 15s

asked Dec 29, 2016 by suganyadevi.p

1 answer

A current vs time graph of the current passing through a solenoid is shown in the fig. For which time in the back electromotive force (u) a maximum? If the back emf at t=3s is e, find the back emf at t = 7s. OA, AB and BC are straight line segments.

asked Dec 29, 2016 by suganyadevi.p

1 answer

Predict the direction of induced current in the situation described above.

asked Dec 29, 2016 by priyanka.c

1 answer

Find the current in the wine PQ for the configuration as shown in the fig. Wire PQ has negligible resistance. B, the magnetic field is coming out of the paper. $\theta$ is a fixed angle made by PQ travelling smoothly over two conducting parallel wires separated by a distance d.

asked Dec 29, 2016 by suganyadevi.p

1 answer

Consider a closed loop C in a magnetic field as shown in the fig. The flex passing through the loop is defined by choosing a surface whose edge coincides with the loop and using the formula $\phi = B_1 . dA_1 + B_2 . dA_2 + ...........$ Now if we choose two different surfaces $S_1$ and $S_2$ having C as their edge, would we get the same answer for flex. Justify.

asked Dec 29, 2016 by suganyadevi.p

1 answer

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