A coil is suspended in a uniform magnetic field, with the plane of the coil parallel to the magnetic lines of force. When a current is passed through the coil it starts oscillating; it is very difficult to stop. But if an aluminium plate is placed near to the coil, it stops. This is due to

• development of air current when the plate is placed.

• induction of electrical charge on the plate

• shielding of magnetic lines of force as aluminium is a paramagnetic material.

• shielding of magnetic lines of force as aluminium is a paramagnetic material.

2.

A boat is moving due east in a region where the earth's magnetic field is 5.0 × 10^-5 NA^-1m^-1 due north and horizontal. The boat carries a vertical aerial 2m long. If the speed of the boat is 1.50 ms^-1, the magnitude of the induced emf in the wire of aerial is

• 0.75 mV

• 0.50 mV

• 0.15 mV

• 0.15 mV

An inductor of inductance L = 400 mH and resistors of resistances R1 = 2 Ω and R2 = 2 Ω is connected to a battery of emf 12 V as shown in the figure. The internal resistance of the battery is negligible. The switch S is closed at t = 0. The potential drop across L as a function of time is 

• 6^e–5t V

• 
• 
• 

Two identical conducting wires AOB and COD are placed at right angles to each other. The wire AOB carries an electric current I₁ and COD carries a current I₂. The magnetic field on a point lying at a distance ‘d’ from O, in a direction perpendicular to the plane of the wires AOB and COD, will be given by

The flux linked with a coil at any instant ‘t’ is given by
φ= 10t²- 50t +250
The induced emf at t = 3 s is

• 190 V

• −190 V

• -10 V

• -10 V

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

A coil having n turns and resistance 4R Ω. This combination is moved in time t seconds from a magnetic field W₁ weber to W₂ weber. The induced current in the circuit is

A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 radians per second. If the horizontal component of earth’s magnetic field is 0.3 × 10⁻⁴ T, then the e.m.f. developed between the two ends of the conductor is

• depends on the nature of the metal used

• depends on the intensity of the radiation

• depends both on the intensity of the radiation and the metal used

• depends both on the intensity of the radiation and the metal used