An electric dipole of moment µ of 400 µC m

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 Multiple Choice QuestionsMultiple Choice Questions

21.

Two infinitely long parallel plates of equal areas 6 cm2 are separated by a distance of 1 cm. While one of the plates has a charge of + 10 nC and the other has − 10 nC. The magnitude of the electric field between the plates, if ε0 = 10-936π F/m is

  • 0.6 π kV/m

  • 6 π kV/m

  • 600 π kV/m

  • 60 π V/m


22.

The electric field strength in NC-1 that is required to just prevent a water drop carrying a charge 1.6 x10-19 C from falling under gravity is (g = 9.8 ms-2, mass of water drop = 0.0016 g)

  • 9.8 × 10-16

  • 9.8 × 1016

  • 9.8 × 10-13

  • 9.8 × 1013


23.

A cylinder of radius r and length l is placed in a uniform electric field of intensity E acting parallel to the axis of the cylinder. The total flux over curved surface area is

  • 2πrE

  • 2πlE

  • Zero

  • E2πrl


24.

Electric lines of force about a positive point charge are

  • radially outwards

  • circular clockwise

  • radially inwards

  • parallel straight lines


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25.

An electric dipole of moment µ of 400 µC m is placed in a transverse electric field (E) of 50 Vm-1 at an angle of 30° to E. Then, a torque of

  • 10-2 Nm acts along the direction E

  • 10-3 Nm acts along the direction µ

  • 10-2 Nm acts normal to both E and µ

  • 10-3 Nm acts along the direction E


C.

10-2 Nm acts normal to both E and µ

Given, P = 400 µC = 400 × 10-6 C

          E = 50 Vm-1

          θ = 30°

We know that, torque acting on an electric dipole,

          ζ = PEsin θ

where, P = dipole moment

              = 400 × 10-6 × 50 × sin 30°

              = 400 × 10-6 × 50 × 12

              = 200 × 50 × 10-6

              = 10-2 N-m

This torque will act normal to both E and µ.


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26.

The velocity acquired by a charged particle of mass m and charge Q accelerated from rest by a potential of V is

  • QVm

  • mQv

  • 2QVm

  • mQV


27.

An electron moving with a constant velocity v along X-axis enters a uniform electric field applied along Y-axis. Then, the electron moves

  • with uniform acceleration along Y-axis

  • without any acceleration along Y-axis

  • in a trajectory represented as y = ax2

  • in a trajectory represented as y = ax


28.

A plane square sheet of charge of side 0.5 m has uniform surface charge density. An electron at 1 cm from the centre of the sheet experiences a force of 1.6 x 10-12 N directed away from the sheet. The total charge on the plane square sheet is (ε0 = 8.854 × 10-12 C2 m-2 N-1)

  • 16.25 µC

  • − 22.15 µC

  • − 44.27 µC

  • 144.27 µC


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29.

The time period of revolution of a charge q1 and of mass m moving in a circular path of radius r due to Coulomb force of attraction with another charge q2 at its centre is

  • 16πε0mr3q1q2

  • 8π2ε0mr3q1q2

  • ε0mr316 q1q2

  • 16π3ε0mr3q1q2


30.

When a comb rubbed with dry hair attracts pieces of paper. This is because the

  • comb polarizes the piece of paper

  • comb induces a net dipole moment opposite to the direction of field

  • electric field due to the comb is uniform

  • comb induces a net dipole moment perpendicular to the direction of field


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