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

1. positive
2. negative
3. zero
4. none of the above
EXPLANATION
There is no electric field inside a charged conductor. Therefore the answer is zero.

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

1. 4 μCm-2
2. 20 μCm-2
3. 8 μCm-2
4. 0
EXPLANATION
No answer description required for this question.

48) The electric potential at the surface of an atom nucleus of radius 9×10-15 m is

1. 40 V
2. 8×106 V
3. 9 V
4. 120 V
EXPLANATION
No answer description required for this question.

49) An α-particle is accelerated through a potential difference of 104 V. The gain in K.E of the α-particle is

1. 2×10-4 eV
2. 2×104 J
3. 2×10-4 eV
4. none of the above
EXPLANATION
K.E = Charge×P.D = 2×104 eV.

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

1. 2×10-3 C
2. 3×10-6 C
3. 2×10-4 C
4. 2×10-5 C
EXPLANATION
No answer description required for this question.

51) If a charge is moved against the coulomb force of an electric field, then

1. the strength of electric field is decreased
2. the energy of the system is decreased
3. work is done by the electric field
4. energy is used by some outside source
EXPLANATION
No answer description required for this question.

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

1. 2.3×10-3 ms-1
2. 2.3×107 ms-1
3. 4.6×104 ms-1
4. 0.23×1012 ms-1
EXPLANATION
The electric electrostatic fields are conservative in terms of energy.
The energy lost by the electron = V e = 1500×1.602 * 10⁻¹⁹  Joules
= 2.403×10-16 J

P.E =1/2 mv2 = 1/2 × 9.11×10⁻³¹ × v2

v=2.3×107 ms-1

53) A cloud is at potential of 8×106 V relative to the ground. A charge of 40 C is transferred in lightening stroke between the cloud and the ground. The energy dissipated is

1. 3.2×10-7 J
2. 6.4×108 J
3. 3.2×10-6 J
4. 3.2×108 J
EXPLANATION
Energy dissipated = Charge×P.D = 40×(8×106) = 3.2×108

54) Proton has a mass of 1840 times that of an electron. If a proton is accelerated from rest by a P.D of 1 V, its K.E is

1. 1840 eV
2. 1 MeV
3. 1 eV
4. none of the above
EXPLANATION
No answer description required for this question.

55) A uniform wire of length 5 m is carrying a steady current. The electric field inside  it is 0.2 N/C. The P.D across the ends of the wire is

1. 1 V
2. 0.5 V
3. 10 V
4. 0.1 V
EXPLANATION
No answer description required for this question.

56) A capacitor of 200 μF is charged to a potential of 100 V. The stored energy in watt seconds will be

1. 200
2. 100
3. 50
4. 0
EXPLANATION
No answer description required for this question.

57) A capacitance C is charged through a resistance R. The time constant of the charging circuit is

1. R/C
2. 1/RC
3. RC
4. C/R
EXPLANATION
No answer description required for this question.

58) A 3 μF capacitor is given charge of 2×10-3 coulombs. The potential difference between the plates in volts is

1. 30
2. 0.30
3. 0.003
4. 3000
EXPLANATION
No answer description required for this question.

59) A capacitor of 40 μf is charged to a potential difference of 500 V. The energy stored in the electric field between the plates of this conductor is

1. 4.5 J
2. 4 J
3. 5 J
4. 40 J
EXPLANATION
No answer description required for this question.

60) A capacitor of 100 μF is connected in series with a resistance of 1000 Ω. The time constant of the circuit is

1. 0.001 sec
2. 0.01 sec
3. 0.1 sec
4. 1 sec