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

• 1 mV

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

• 
• 
• 
• 

B.

(W₁ and W₂ are not the magnetic fields, but the values of flux associated with one turn of coil)

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.

• electromagnetic induction in the aluminium plate giving rise to electromagnetic damping.

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

• 0.3 s

B.

0.1 s

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

• is the same for all metals and independent of the intensity of the radiation.