Practice paper · Mid-term

Electrostatic force between two small spheres at separation 'r' is 'F'. Now both spheres come in contact and again placed at separation 'r' then electrostatic force between them is 16F/15. Then ratio of charges is: -

1. A3 /4
2. B1 /2
3. C3/ 5
4. D7/ 2.

A capacitor of capacitance C = 900 pF is charged by 100 V battery, when it gets fully charged then it is disconnected from the battery and connected to another uncharged capacitor of capacitance C = 900 pF. The ratio of electrostatic energy stored by the system before and after disconnection of the battery is:

1. A1:1
2. B1:2
3. C2:1
4. D1:3

Two wires X and Y are made of same material. The wire Y has twice the diameter and half the length as that of wire X. If the resistance of the wire X is R, then resistance of the wire Y will be:

1. AR/3
2. BR/2
3. C2R/5
4. DR/8

Two electric bulbs of the same power, but with different marked voltages are connected in series across a power line. Their brightness will be: -

1. Adirectly proportional to their marked voltages
2. Binversely proportional to their marked voltages
3. Cdirectly proportional to the squares of their marked voltages
4. Dinversely proportional to the squares of their marked voltages

A particle with charge q moving with velocity v⃗ = v₀ î enters a region with magnetic field B⃗ = B₁ ĵ + B₂ k̂. The magnitude of force experienced by the particle is:

1. Aqv₀ (B₁ + B₂)
2. Bq√v₀ (B₁ + B₂)
3. Cqv₀ √(B₁² + B₂²)
4. Dq√v₀ (B₁² + B₂²)

A long straight wire is held vertically and carries a steady current in upward direction. The shape of magnetic field lines produced by the current-carrying wire are:

1. Ahorizontal straight lines directed radially out from the wire.
2. Bstraight lines parallel to the current-carrying wire.
3. Cconcentric horizonal circles around the wire.
4. Dcoaxial helixes around the wire.

A bar magnet is initially at right angles to a uniform magnetic field. The magnet is rotated till the torque acting on it becomes one-half of its initial value. The angle through which the bar magnet is rotated is:

1. A300
2. B450
3. C600
4. D750

The self-inductance L of a solenoid of length λ and area of cross-section A, with a fixed number of turns N increases as:

1. Aλ and A increase.
2. Bλ decreases and A increases.
3. Cλ increases and A decreases.
4. Dboth λ and A decrease.