Explore topic-wise InterviewSolutions in .

False.

Correct: A glass rod rubbed with silk attract an ebonite rod rubbed with fur.

Correct option is D) All the above

1. Bulb is an electric device which converts electrical energy into light energy. 

2. There are different types at bulbs. 

They are 

1) incandescent bulb, 

2) Fluorescent bulb (Tube light), 

3) CFL (Compact Fluorescent Lamp), 

4) LED bulb, etc. 

3. Incandescent bulb works on the principle of heating effect of electricity. 

4. Incandescent bulb doesn’t save electrical energy. It consumes more electrical energy compared to CFL and LED lamps.

Correct option is A) L.E.D. Bulb

1. LED 

2. Incandescent 

3. LED 

4. Incandescent.

The electrical power of a single tube in kilowatt = \(\frac{40}{1000}\) = 0.040 kW

The electrical power of 5 tubes in kilowatt = 0.2kW

Total unit of power consumed = 0.2 × 20 = 4kWh = 4units 

The cost of electricity consumed = 4 × 0.50 = Rs. 2

The brightness of a bulb is representation of the power dissipated by the bulb.

The power is given by

P = \(\frac{V^2}{R}\)

So, the dimmer bulb has larger resistance.

The resistance of a heater coil is less than that of electric bulb filament. When heater is switched on in parallel, more current start flowing through the heater coil and current through the bulb filament decreases making it dim. After some time, when heater coil becomes hot its resistance increases. As a result,current through the heater coil decreases and the current through the bulb filament increases and thus dimness of the bulb decreases.

Volt meter is a device that helps to maintain a potential difference across a conductor.

Correct Answer is: (a) +2

The line integral gives the work done in bringing a unit positive charge, on which the force is Vector E, from ∞ to the centre of the ring. This is equal to the potential at the centre, taking the potential at ∞ to be zero. Its value is V k = Q/R = 9 x 109 x 1.11 x 10^-10 / 0.5 = 2 V.

Correct Answer is: (c) R/3

Using the expression of the previous question’s answer, for r = 0, potential at the centre = V_c = k 3Q/2R. 

We require a point where V = V_c/2 = k 3Q/4R.

This point cannot lie inside the sphere where V ≥ k Q/R.

Let the point lie outside the sphere, at a distance r from the centre. Then,

V = k Q/r = k 3Q/4R

or r = 4/3 R

Distance from the surface = r - R = R/3.

Correct Answer is: (c)

V = k Q/2R³(3R² - r²).

Correct Answer is: (b, d)

As A and C are earthed, they are connected to each other. Hence, ‘A + B’ and ‘B + C’ are two capacitors with the same potential difference. If B is closer to A than to C then the capacitance C_AB is > C_BC. The upper surface of B will have greater charge than the lower surface. As the force of attraction between the plates of a capacitor is proportional to Q ², there will be a net upward force on B. This can balance its weight.

Correct Answer is: (a, b & c)

Correct Answer is: (b, d)

As on touching the disc with the charged rod, divergence in the leaves decreases, this means the rod has opposite kind of charge than leaves i.e. rod has negative charge.

Correct Answer is: (c) either inside or outside the shell

Use Gauss’s theorem.

Correct Answer is: (b) r(n - 1) 

At the centre, the intensity is effectively due to one charge and the potential is due to (n - 1) charges.

Correct Answer is: (a) k Q/r² 

If charges were placed at all the corners, the field at the centre would be zero. Hence, the field at the centre due to any one charge is equal (and opposite) to the field due to all the other (n - 1) charges.

Correct Answer is: (d) F/8

F = k 2Q²/d², where d = separation.

Since charge is shared, the charge on each ball = 1/2 (2Q - Q) = Q/2.

The force now becomes F' = k (q/2)²/d² = 1/4. k Q²/d² = F/8.

Correct Answer is: (d) kπλ

The total charge on the half ring is πRλ. As all points on the ring are at a distance R from the centre, the potential at the centre is

V = k πRλ/R = kπλ.

Current flows more easily through a thick wire. Because if the wire is thick resistance is less. Therefore thick wire is required.

The resistance of the conductor depends:

1. on its length

2. on its area of cross section and

3. on the nature of its material.

This is a resistor which does not obey Ohm’s Laws. V -I graph for non-ohmic resistor is not a straight line.

Resistance do not depend on the voltage it depends on the material of the resistor whether the intermolecular force of attraction is strong or loose which decides the resistance.