A magnet N-S is suspended from a spring and when it oscillates, t

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 Multiple Choice QuestionsMultiple Choice Questions

91.

Two long straight wires are set parallel to each other. Each carries a current in the same direction and the separation between them is 2 r. The intensity of the magnetic field mid-way between them is

                   

  • μ0ir

  • 4μ0ir

  • Zero

  • μ0i4r


92.

A galvanometer of resistance 20 Ω is to be converted into an ammeter of range 1 A. If a current of 1 mA produces full scale deflection, the shunt required for the purpose is

  • 0.01 Ω

  • 0.05 Ω

  • 0.02 Ω

  • 0.04 Ω


93.

A magnetic needle is kept in a non-uniform magnetic field. It experiences

  • force and torque

  • a force but not a torque

  • a torque but not a force

  • neither a force nor a torque


94.

A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is

  • 3B

  • 5B

  • 4B

  • 2B


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95.

To send 10% of the main current through a moving coil galvanometer of resistance 99 ohm, the shunt required is

  • 10 ohm

  • 9.9 ohm

  • 9 ohm

  • 11 ohm


96.

A charged particles moves along the line AB which lies in the same plane of a circular loop of conducting wire as shown in the figure. Then

            

  • no current will be induced in the loop

  • the current induced in the loop will change its direction as the charged particle passes by

  • the current induced will be anti-clockwise

  • the current induced will be clockwise


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97.

A magnet N-S is suspended from a spring and when it oscillates, the magnet moves in and out of the coil C. The coil is connected to a galvanometer G. Then, as the magnet oscillates

              

  • G shows no deflection

  • G shows deflection to the left and right but the amplitude steadily decreases.

  • G shows deflection to the left and right with constant amplitude.

  • G shows deflection on one side.


B.

G shows deflection to the left and right but the amplitude steadily decreases.

When the S-pole of a magnet is moved towards the coil, then by Lenz's law the face of coil, towards magnet becomes S-pole and the current flows clockwise to cancel change in the magnetic flux. So, to bring the magnet near to the coil, more work has to be done against the force of repulsion produced between them. So, the galvanometer shows deflection to the left. Now when the S-pole is moved away, a current flows in anti-clockwise direction to make the face of the coil towards magnet, a N-pole. Thus, will try to attract the magnet. So, the galvanometer shows the deflection to the right.

      

Since, flux varies hence, amplitude will not be constant and will decrease.


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98.

The maximum current that can be measured by a galvanometer of resistance 40 Ω, is 10 mA. It is converted into a voltmeter that can read upto 50 V. The resistance to be connected in series with the galvanometer (in ohms) is

  • 2010

  • 4050

  • 5040

  • 4960


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99.

A rectangular coil of 300 turns has an average area of 25 cm x 10 cm . The coil rotates with a speed of 50 cps in uniform magnetic field of strength 4 × 10-2 T about an axis perpendicular to the field. The peak value of the induced emf is (in volt)

  • 300 π

  • 3000 π

  • 3 π

  • 30 π


100.

A vertical circular coil ofradius 0.1 m and having 10 turns carries a steady current. When the plane of the coil is normal to the magnetic meridian, a neutral point is observed at the centre of the coil. If BH = 0314 × 10-4 T, the current in the coil is

  • 0.5 A

  • 0.25 A

  • 2 A

  • 1 A


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