Magnetic Effect...

Directions: The following question has four choices out of which only one is correct.

A bar magnet of length 3 cm has points A and B along its axis at distances of 24 cm and 48 cm, respectively, on the opposite sides.



Ratio of the magnitudes of the magnetic fields at these points will be

The effective length of a magnet is 31.4 cm and its pole strength is 0.5 A-m. What will be the magnetic moment if it is bent in the form of a semicircle?

A magnet of magnetic moment 20 CGS units is freely suspended in a uniform magnetic field of intensity 0.3 CGS units. The amount of work done in deflecting it by an angle of 30° (in CGS units) is

A steel wire of length 'l' has a magnetic moment M. It is bent into a semicircular arc. The new magnetic moment is

At a point on the axial line of a bar magnet of dipole moment M, the magnetic potential is V. What is the magnetic potential due to a bar magnet of dipole moment M/4 at the same point?

Directions: For the statements of Assertion and Reason, mark the correct answer.

(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If both assertion and reason are false.

Assertion: A disc-shaped magnet levitates above a superconducting material that has been cooled by liquid nitrogen.
Reason: Superconductors repel a magnet.

A loosely wound helix made of stiff wire is mounted vertically with the lower end just touching a dish of mercury. When a current from the battery is started in the coil through the mercury, then

A proton and an alpha particle enter a uniform magnetic field with the same velocity. The period of revolution of the alpha particle will be

When an electron moves in a magnetic field in a direction perpendicular to the field, then its path will be

An electron of mass m and charge q is travelling with a speed v along a circular path of radius r at a right angle to a uniform magnetic field of intensity B. If the speed of the electron is doubled and the intensity of magnetic field is halved, the resulting path would have a radius

The magnetic field due to a straight conductor of uniform cross-section of radius 'a' and carrying a steady current is represented by

A wire PQR is bent as shown in the figure and is placed in a region of a uniform magnetic field B. The length of PQ = length of QR = L. A current l ampere flows through the wire as shown. The magnitude of the force on PQ and QR respectively will be

A straight wire of mass 200 g and length 1.5 m carries a current of 2 A. It is suspended in mid-air by a uniform horizontal magnetic field B. The magnitude of B (in tesla) is (assume g = 9.8 ms^-2)

A vertical straight conductor carries a current vertically upwards. A point P lies to the east of it, at a small distance and another point Q lies to the west of it, at the same distance. The magnetic field at P is

A proton, a deuteron and an alpha particle, each having the same KE are moving in circular trajectories in a constant magnetic field. If the radii trajectories of these particles are r_p, r_d and r_a respectively, then