A magnetic field of 2x10⁻² T acts at right angles to a coil of area 100 cm² with 5O turns. The average emf induced in the coil is 0.1 V. When it is removed from the field in time t,  the value of t is

• 0.1 s

• 0.01 s

• 1 s

• 10 s

A battery of four cells in series,each having an emf of 1 .4 V and an internal resistance of 2 $\mathrm{\Omega }$ is to be used to charge a small 2 V accumulator of negligible internal resistance. What is the charging current?

• 0.1 A

• 0.2 A

• 0.3 A

• 0.45 A

If the energy of a 100 $\mathrm{\mu }$F capacitor charged to 6 kV could all be used to lift a 5O kg mass, what would be the greatest vertical height through which mass could be raised?

• 0.6 mm

• 3.6 m

• 1.2 mm

• 12 m

A pan containing a layer of uniform thickness of ice is placed on a circular turntable with its centre coinciding with the centre of the turntable. The turntable is now rotated at a constant angular velocity about a vertical axis passing through its centre and the driving torque is withdrawn. There is no friction between the table and the pivot. The pan rotates with the table. As the ice melts

• the angular velocity of the system decreases

• the angular velocity of the system increases

• the angular velocity of the system remains unchanged

• the moment of inertia of the system decreases

A sheet of aluminium foil of negligible thickness is introduced between the plates of a capacitor. The capacitance of the capacitor

• decreases

• remains unchanged

• becomes infinite

• increases

A metal wire of linear mass density of 9.8 g/m is stretched with a tension of 10 kg-wt between two rigid supports 1m apart. The wire passes at its middle point between the poles of a permanent magnet and it vibrates in resonance when carrying an alternating current of frequency η. The frequency η of the alternating source is 

• 50 Hz

• 100 Hz

• 200 Hz

• 25 Hz

If the electric fluxes entering and leaving an enclosed surface respectively are  Φ₁ and Φ_2, the electric charge inside the surface will be

• (Φ₂ − Φ₁) ε₀

• (Φ₁ + Φ₂) / ε₀

• (Φ₂ − Φ₁) / ε₀

• (Φ₁ + Φ₂) / ε₀

38.

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon

• the rates at which currents are changing in the two coils

• relative position and orientation of the two coils

• the materials of the wires of the coils

• the currents in the two coils

An ammeter reads upto 1 A. Its internal resistance is 0.81 Ω. To increase the range to 10 A, the value of the required shunt is

• 0.03 Ω

• 0.3 Ω

• 0.9 Ω

• 0.09 Ω

The thermo-emf of a themocouple is 25µV /°C at room temperature. A galvanometer of 40Ω resistance, capable of detecting current as low as 10^-5 A, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is

• 16°C

• 12°C

• 8°C

• 20°C