A wire PQR is bent as shown in figure and is placed in a region o

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 Multiple Choice QuestionsMultiple Choice Questions

101.

A current flows in a conductor from east to west. The direction of the magnetic field at a point above the conductor is

  • towards east

  • towards west

  • towards north

  • towards south


102.

A tangent galvanometer has a reduction factor of 1 A and it is placed with the plane of its coil perpendicular to the magnetic meridian. The deflection produced when a current of 1 A is passed through it is

  • 60°

  • 45°

  • 30°

  • None of these


103.

An electric field of 1500 V/m and a magnetic field of 0.40 weber/metre2 act on a moving electron. The minimum uniform speed along a straight line the electron could have is

  • 1.6 × 1015 m/s

  • 6 × 10-16 m/s

  • 3.75 × 103 m/s

  • 3.75 × 102 m/s


104.

In an ammeter 10% of main current is passing through the galvanometer. If the resistance of the galvanometer is G, then the shunt resistance, in ohms is

  • 9G

  • G9

  • 90G

  • G90


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105.

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

  • 2r

  • 4r

  • r/4

  • r/2


106.

A galvanometer coil has a resistance of 15 Ω and gives full scale deflection for a current of 4 mA. To convertit to an ammeter of range 0 to 6 A

  • 10 m Ω resistance is to be connected in parallel to the galvanometer

  • 10 m Ω resistance is to be connected in series with the galvanometer

  • 0.1 Ω resistance is to be connected in parallel to the galvanometer

  • 0.1 Ω resistance is to be connected in series with the galvanometer


107.

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)

  • 2

  • 1.5

  • 0.55

  • 0.65


108.

A solenoid 1.5 m long and 0.4 cm in diameter possesses 10 turns per cm length. A current of 5 A falls through it. The magnetic field at the axis inside the solenoid is

  • 2π × 10-3 T

  • 2π × 10-5 T

  • 4π × 10-2 T

  • 4π × 10-3 T


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109.

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

          

  • BIl, 0

  • 2 BIl, 0

  • 0, BIl

  • 0,0


C.

0, BIl

The Lorentz force acting on the current carrying conductor in the magnetic field is

           F = IBl sin θ

Since, wire PQ is parallel to the direction of magnetic field, then θ = 0,

∴    FPQ = IBl sin 0° = 0

Also, wire QR is perpendicular to the direction of magnetic field, then θ = 90°.

∴    FQR = IBl sin 90° = IBl


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110.

A circular coil carrying a certain current produces a magnetic field B0 at its centre. The coil is now rewound so as to have 3 turns and the same current is passed through it. The new magnetic field at the centre is

  • B09

  • 9B0

  • B03

  • 3B0


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