41.

One conducting U tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. if each tube moves towards the other at a constant speed V, then the emf induced in the circuit in terms of B,

• B

• -B

• zero

• zero

Two thin, long parallel wires separated by a distance  ‘d’ carry a current of ‘i’ A in the same direction. They will

• attract each other with a force of µ0i²/(2πd) 

• repel each other with a force of µ0i²/(2πd)

• attract each other with a force of µ0i²(2πd² )

• attract each other with a force of µ0i²(2πd² )

A charged ball B hangs from a silk thread S which makes an angle θ with a large charged conducting sheet P, as shown in the figure. The surface charge density σ of the sheet is proportional to

• cos θ

• cot θ

• sin θ

• sin θ

Two point charges + 8q and – 2q are located at x = 0 and x = L respectively. The location of a point on the x axis at which the net electric field due to these two point charges is zero is

• 2L

• L/4

• 8L

• 8L

Two thin wires rings each having a radius R are placed at a distance d apart with their axes coinciding. The charges on the two rings are +q and –q. The potential difference between the centres of the two rings is 

• 
• 

• zero

• zero

A parallel plate capacitor is made by stacking n equally spaced plates connected alternatively. If the capacitance between any two adjacent plates is C then the resultant capacitance is

• (n − 1)C

• (n + 1)C

• C

• C

Two concentric coils each of radius equal to 2π cm are placed at right angles to each other. 3 Ampere and 4 ampere are the currents flowing in each coil respectively. The magnetic induction in Weber/m² at the centre of the coils will be (µ0 = 4π × 10⁻⁷ Wb/A^-m)

• 12 × 10⁻⁵

• 10⁻⁵

• 5 × 10⁻⁵

• 5 × 10⁻⁵

A coil of inductance 300 mH and resistance 2Ω is connected to a source of voltage 2V. The current reaches half of its steady state value in

• 0.05 s

• 0.1 s

• 0.15 s

• 0.15 s

The self inductance of the motor of an electric fan is 10 H. In order to impart maximum power at 50 Hz, it should be connected to a capacitance of

• 4µF

• 8µF

• 1µF

• 1µF

An energy source will supply a constant current into the load of its internal resistance is

• equal to the resistance of the load.

• very large as compared to the load resistance.

• zero

• zero