31) The electric field intensity on the surface of a charged conductor is

1. zero
2. directed normally to the surface
3. directed tangentially to the surface
4. directed along 45° to the surface
EXPLANATION
No answer description required for this question.

32) A capacitor having a capacitance of 30 μf is connected across a 200 V dc source. The charging current will be least

1. initially
2. when capacitor is half charged
3. when capacitor is fully charged
4. when capacitor is almost 90% charged
EXPLANATION
No answer description required for this question.

33) Out of the material given below, which has the highest dielectric strength

1. glass
2. mica
3. oiled paper
4. air
EXPLANATION
No answer description required for this question.

34) Two equal and similar charges are placed a finite distance apart. A third equal and dissimilar charge is placed midway between them. The third charge will be

1. in stable equilibrium
2. in unstable equilibrium
3. neutralized
4. oscillating
EXPLANATION
If the third charge is moved slightly towards one of the charges, it would experience greater attraction due to that charge compared to the other one. Therefore, the third charge is in unstable equilibrium.

35) The positive terminal of a 12 V battery is earthed. The negative terminal will be at

1. 0 V
2. 12 V
3. -12 V
4. 24 V
EXPLANATION
If the positive terminal connect to earth than there will be no charge pass through it due to open circuit.

36) 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

1. 900 J
2. 400 J
3. 100 J
4. 300 J
EXPLANATION
K.E = Q×P.D = 0.3×1000 = 300 J

37) Two copper spheres A and B are of the same radii. Sphere A is hollow and Sphere B is solid. If both spheres are charged to the same potential

1. Both will hold the same charge
2. A will hold more charge as compared to B
3. B will hold more charge as compared to A
4. Both will not hold any charge
EXPLANATION
If they both have the same potential, they both have the same charge, since the charge resides on the surface of the items and the spheres are metal, hence the potential is constant within spheres.

38) For dielectrics, flux is proportional to

1. potential difference between electrodes
2. resistivity of medium
3. rate of change of potential difference
4. rate of change of current
EXPLANATION
We know that the formula for capacitance is C = Q / V, this becomes Q = C × V. Hence, this expression clearly says that the dielectric flux or charge ‘Q’ is directly proportional to potential difference ‘V’.

39) For a capacitance of 10 μf the potential difference is increased uniformly from 0 to 600 V in 2 seconds. The charging current must be

1. 1 mA
2. 3 mA
3. 5 mA
4. 10 mA
EXPLANATION
Charging Current = C (V/t)

I = 10×10-6(600/2)

I = 3×10-3A

40) The capacitance between two plates increases with

1. larger plate area and shorter distance between plates
2. shorter plate area and shorter distance between them
3. shorter plate area and higher applied voltage
4. larger plate area, longer distance between plates and higher applied voltage
EXPLANATION
No answer description required for this question.

41) The charge on a capacitor is 1.5×10-2 coulombs when the potential difference across its plates is 750 V. The elastance of the capacitor will be

1. 0.5 mega daraf
2. 1 mega daraf
3. 11.2 mega daraf
4. 22.7 mega daraf
EXPLANATION
Electrical elastance is the inverse of capacitance. So,

D =V/Q

D = 750/(1.5×10-2)

D = 0.5 mega daraf

42) The current in a single element circuit leads the voltage 65° at all time. The circuit element is

1. a resistor
2. an inductor
3. a capacitor
4. any of the above
EXPLANATION
No answer description required for this question.

43) A parallel plate capacitor connected to a battery stores twice as much charge with a given dielectric as it does with air as dielectric, the susceptibility of the dielectric is

1. 0
2. 1
3. 2
4. 3
EXPLANATION 44) A capacitor is charged and source is then disconnected. When the plates are now separated

1. charge changes
2. charge and potential difference both change
3. charge and potential difference remain constant
4. potential difference changes
EXPLANATION
If the capacitor is connected across a battery, the voltage will stay constant at the battery voltage. When the capacitor is charged and disconnected, the voltage will rise. Assume the capacitor holds charge Q, then

Q = CV, or V = Q/C

Separating the plates reduces C, so if Q remains constant V must increase proportionally.

45) A sphere of 1 meter radius can attain a maximum potential of

1. 1000 V
2. 2 kV
3. 30 kV
4. 3×106 V