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 Multiple Choice QuestionsMultiple Choice Questions

21.

Two spherical conductors B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged, is brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion between B and C is

  • F4

  • 3 F4

  • F8

  • 3 F8


22.

A charge q is located at the centre of a cube. The electric flux through any face is

  • 4 πq6 4πεo

  • πq6 4πεo

  • q6 4πεo

  • 2πq6 4πεo


23.

Three equal charges, each having a magnitude of 2.0 x 10-6 C, are placed at the three corners of a right angled triangle of sides  3 cm,  4 cm  and  5 cm. The force (in magnitude) on the charge at the right angled corner is

  • 50 N

  • 26 N

  • 29 N

  • 45.9 N


24.

Two charges of + 10 μC and +20 μC are separated by a distance 2 cm. The net potential (electric) due to the pair at the middle point of the line joining the two changes, is

  • 27 MV

  • 18 MV

  • 20 MV

  • 23 MV


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25.

The charges on two spheres are + 7 µC and -5C respectively. They experience a force F. If each of them is given an additional charge of -2 µC, then the new force of attraction will

  • F

  • F2

  • F3

  • 2F


26.

A square loop ABCD, carrying a current I2, is placed near and coplanar with a long straight conductor XY carrying a current I1, as shown in figure. The net force on the loop will be

     

  • μ0 I1 I22 π

  • μ0 I1I2 L2 π

  • 2 μ0 I1I2 L3 π

  • 2μ0 I1 I23 π


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27.

Three identical charges are placed at the vertices of an equilateral triangle. The force experienced by each charge, ( if k = 1/4π ε0 ) is

  • 2k q2r2

  • k q22 r2

  • 3 k q2r2

  • k q22 r2


C.

3 k q2r2

              

The magnitude of the force is given by

     F = k q1 q2r2

Force on charge q at A:

( i ) Due to B 

          f = k q × qr2

Along BA

         f = k q2r2 

(ii) Due to C

         f = k q2r2

Along CA

        f = k q2r2

∴  Resultant force = F

        F2 = f2 + f2 + 2f × f × cos 60o 

        F2 = 2f22 f2 × 12

       F2 = 3 f2

⇒     F = 3 f

⇒    Resultant force = 3 kq2r2


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28.

The angle of dip at a certain place where the horizontal and vertical components of the earth's magnetic field are equal is

  • 30o

  • 75o

  • 60o

  • 45o


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29.

Assertion:  Lines of force are perpendicular to conductor surface.

Reason:  Generally electric field is perpendicular to equipotential surface.

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

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

  • If assertion is true but reason is false.

  • If both assertion and reason are false.


30.

The force per unit length between two straight conductors separated by a distance of 0.02 m is 2 x 10-3 N m-1. The current in one conductor is 10 A and that in the other conductor is

  • 20 A

  • 5 A

  • 2 A

  • 10 A


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