The magnetic moment of a current (I) carrying circular coil of ra

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261.

The magnetic moment of a current (I) carrying circular coil of radius (r) and number of turns (n) varies as

  • 1r2

  • 1r

  • r

  • r2


D.

r2

The magnetic  moment of a curren·t carrying conductor is

      i · nπr2 = niA

i.e Magnetic moment ∝  r2


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262.

The cyclotron frequency of an electron  gyrating in a magnetic field of  1 T approximately

  • 28 MHz

  • 280 MHz

  • 2.8 GHz

  • 28 GHz


263.

An electric dipole placed in a non-uniform electric field experiences

  • both a torque and a net force

  • only a force but no torque

  • only a torque but no net force

  • no torque and no net force


264.

Three charges are placed at the vertices of an equilateral triangle of side a as shown in the given figure. The force experienced by the charge placed at the vertex A in a direction normal to BC is

  • Q2 / 4πε0a2

  • - Q2 (4πε0a2<)

  • zero

  • Q2 / 2πε0a2


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265.

The earth's magnetic field at a  given point is 0.5 × 10-5 Wb/m2. This field is to be annulled by magnetic induction at the centre of a circular conducting loop of radius 5.0 cm. The current required to be flown in the loop nearly

  • 0.2 A

  • 0.4 A

  • 4 A

  • 40 A


266.

The difference in lengths of a mean solar day and a sideral day is about 

  • 1 min

  • 4 min

  • 15 min

  • 56 min


267.

The coefficient of mutual inductance, when magnetic flux changes by 2 x 10-2 Wb and current changes by 0.01 A is

  • 2 H

  • 4 H

  • 3 H

  • 8 H


268.

Assertion:  We cannot think of a magnetic field configuration with three poles. 

Reason:  A bar magnet does exert a torque on itself due to its own field.

  • If both the assertion and reason are true and reason is a correct explanation of the assertion.

  • If both assertion and reason are true but assertion is not a correct explanation of the assertion.

  • If the assertion is true but the reason is false.

  • If both assertion and reason are false


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269.

At a place earth's magnetic field, 5 × 105 Wb/m2 is acting perpendicular to a coil of radius R = 5 cm. If  μο / 4π = 107 , then how much current is induced in circular loop?

  • 0.2 A

  • 0 A

  • 4 A

  • 40 A


270.

A wire length l carries a steady current. It is bent first to form a circular plane loop of one turn. The magnetic field at the centre of the loop is B. The same length is now bent more sharply give a to double loop of smaller radius. The  magnetic field at the centre caused by the same is

  • B

  • B/4

  • 4B

  • B/2


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