Electrical Questions and Answers

1. The force between two electrons separated by a distance r varies as

(i) r2
(ii) r
(iii) r-1
(iv) r-2

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2. Two charges are placed at a certain distance apart. A brass sheet is placed between them. The force between them will

(i) increase
(ii) decrease
(iii) remains unchanged
(iv) none of the above

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3. Which of the following appliance will be studied under electrostatics ?

(i) incandescent lamp
(ii) electric iron
(iii) lightning rod
(iv) electric motor

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4. The relative permittivity of air is

(i) 0
(ii) 1
(iii) 8.854 x 10-12
(iv) none of the above

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5. The relative permittivity of a material is 10. Its absolute permittivity will be

(i) 8.854 x 10-11 F/m
(ii) 9 x 108 F/m
(iii) 5 x 105 F/m
(iv) 9 x 105 F/m

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6. Another name for relative pennittivity is

(i) dielectric constant
(ii) dielectric strength
(iii) potential gradient
(iv) none of the above

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7. The relative permittivity of most materials lies between

(i) 20 and 100
(ii) 10 and 20
(iii) 100 and 200
(iv) 1 and 10

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8. When the relative permittivity of the medium is increased, the force between two charges placed at a given distance apart

(i) increases
(ii) decreases
(iii) remains the same
(iv) none of the above

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9. Two charges are placed at a distance apart. If a glass slab is placed between them, the force between the charges will

(i) be zero
(ii) increase
(iii) decrease
(iv) remain the same

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10. There are two charges of +1 µC and +5µC. The ratio of the forces acting on them will be

(i) 1 : 1
(ii) 1 : 5
(iii) 5 : 1
(iv) 1 : 25

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11. A soap bubble is given a negative charge. Its radius

(i) decreases
(ii) increases
(iii) remains unchanged
(iv) information is incomplete to say anything

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12. The ratio of force between two small spheres with constant charge in air and in a medium of relative permittivity K is

(i) K2 : 1
(ii) 1 : K
(iii) 1 : K2
(iv) K : 1

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13. An electric field can deflect

(i) x-rays
(ii) neutrons
(iii) α-particles
(iv) γ-rays

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14. Electric lines of force enter or leave a charged surface at an angle

(i) of 90°
(ii) of 30°
(iii) of 60°
(iv) depending upon surface conditions

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15. The relation between absolute permittivity of vacuum (εo), absolute permeability of vacuum (µo) and velocity of light (c) in vacuum is

(i) εoµo = c2
(ii) µoo = c
(iii) εoo = c
(iv) 1/(µoεo) = c2

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16. As one penetrates a uniformly charged sphere, the electric field strength E

(i) increases
(ii) decreases
(iii) is zero at all points
(iv) remains the same as at the surface

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17. If the relative permittivity of the medium increases, the electric intensity at a point due to a given charge

(i) decreases
(ii) increases
(iii) remains the same
(iv) none of the above

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18. Electric lines of force about a negative point charge are

(i) circular, anticlockwise
(ii) circular, clockwise
(iii) radial, inward
(iv) radial, outward

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19. An α-particle is accelerated through a potential difference of 104 V. The gain in kinetic energy of the α-particle is

(i) 2 x 10-4 eV
(ii) 2 x 104 J
(iii) 2 x 104 eV
(iv) none of above

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20. Two charged spheres of radii 10 cm and 15 cm are connected by a thin wire. No current will flow if they have

(i) the same charge
(ii) the same energy
(iii) the same field on their surface
(iv) the same potential

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21. Electric potential is a

(i) scalar quantity
(ii) a vector quantity
(iii) dimensionless
(iv) nothing can be said

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22. A charge Q1 exerts some force on a second charge Q2. A third charge Q3 is brought near. The force of Q1 exerted on Q2

(i) decreases
(ii) increases
(iii) remains unchanged
(iv) increases if Q3 is of the same sign as Q1 and decreases if Q3, is of opposite sign

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23. The potential at a point due to a charge is 9 V. If the distance is increased three times, the potential at that point will be

(i) 27 V
(ii) 3 V
(iii) 12 V
(iv) 18 V

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24. A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. The potential at the centre of the sphere is

(i) 10 V
(ii) 0 V
(iii) same as at point 5 cm away from the surface
(iv) same as at point 25 cm away from the surface

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25. If a unit charge is taken from one point to another over an equipotential surface, then

(i) work is done on the charge
(ii) work is done by the charge
(iii) work on the charge is constant
(iv) no work is done

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26. The electric field intensity on the surface of a charged conductor is

(i) zero
(ii) directed normally to the surface
(iii) directed tangentially to the surface
(iv) directed along 45° to the surface

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27. The force between two charges separated by a distance d in air is 10 N. When the charges are placed same distance apart in a medium of dielectric constant εr the force between them is 2 N. What is the value of εr

(i) 0.5
(ii) 20
(iii) 5
(iv) none of above

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28. Two small spheres, each carrying a charge Q, placed d metres apart repel each other with a force F. If one of the spheres is taken around the other one in a circular path of radius r, the work done will be

(i) zero
(ii) F x 2πr
(iii)F x r
(iv) F/2π

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29. The electric potential across part AB of a circuit is 2 V; point A being at higher potential. If a charge 2 C moves from A to B, then energy released is

(i) 2 Joules
(ii) 12 Joules
(iii) 8 Joules
(iv) 4 Joules

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30. Out of the materials given below, which has the highest dielectric strength ?

(i) glass
(ii) mica
(iii) oiled paper
(iv) air

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31. Two equal and similar charges are placed a finite distance apart. A third equal and dissimilar charge is placed mid-way between them. The third charge will be

(i) in stable equilibrium
(ii) in unstable equilibrium
(iii) neutralised
 (iv) oscillating

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32. The positive temllnal of a 12 V battery is earthed. The negative terminal will be at

(i) zero potential
(ii) +12 V
(iii) -12 V
(iv) +24 V

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33. A tiny particle carrying a charge of 0.3 C is accelerated through a potential difference of 1000 V. The kinetic energy acquired by the particle is

(i) 900 J
(ii) 400 J
(iii) 100 J
(iv) 300 J

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34. Two charges +3 µC and -12 µC are separated by a distance of 0.4 m. Where should a third charge of +3 µC be placed from +3 µC so that it experiences zero force?

(i) 0.4m
(ii) 0.2m
(iii) 0.3m
(iv) 0.1m

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35. For a dipole electric field varies as

(i) r-2
(ii) r-3
(iii) r-1
(iv)  r-4

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36. If a charge is moved against the coulomb force of an electric field, then,

(i) the strength of electric field is decreased
(ii) the energy of the system is decreased
(iii) work is done by the electric field
(iv) energy is used by some outside source

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37. When a charge is brought from infinity along the perpendicular bisector of a dipole, the work done is

(i) positive
(ii) negative
(iii) zero
(iv) none of above

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38. A hollow insulated conducting sphere is given a positive charge of 10 µC. What will be the electric field at the centre of sphere if its radius is 2 m ?

(i) 4 µC m-2
(ii) 20 µC m-2
(iii) 8 µC m-2
(iv) zero

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39. The electric potential at the surface of an atom nucleus (Z = 50) of radius 9.0 x 10-15 m is

(i) 40V
(ii) 8 x 106 V
(iii) 9 V
(iv) 120 V

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40. The insulation property of air breaks down at E= 3 x 106 V/m. The maximum charge that can be given to a sphere of diameter 5 m is approximately

(i) 2 x 10-3 C
(ii) 3 x 10-6 C
(iii) 2 x 10-4 C
(iv) 3 x 10-5 C

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41. Electrons are caused to fall through a potential difference of 1500 V. If they were initially at rest, their final speed is

(i) 2.3 x 103 ms-1
(ii) 2.3 x 107 ms-1
(iii) 4.6 x 104 ms-1
(iv) 0.23 x 1012 ms-1

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42. The ratio of force between two small conducting spheres charged to constant potentials in air and a medium of dielectric constant 2 is

(i) 1 : 2
(ii) 2 : 1
(iii)1 : 4
(iv) 4 : 1

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