The magnetic flux in a closed circuit of resistance 10 Ω varies with time t (in second) as $\mathrm{\pi }$ = (4t² − 5t + 1)Wb. The magnitude of induced current at t = 0.20 s is

• 0.12 A

• 0.38 A

• 0.34 A

• 0.12 A

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

• 4µF

• 8µF

• 1µF

• 2µF

Three solenoid coils of same dimensions, same number of turns and same number of layers of windings are taken. Coil 1 with inductance L₁ was wound using a wire of resistance 11 Ω /m, coil 2 with inductance L₂ was wound using the similar wire but the direction of winding was reversed in each layer, coil 3 with inductance L₃ was wound using a superconducting wire. The self inductance of the coils L₁ , L₂ and L₃ are

• L₁ = L₂ = L₃

• L₁ = L₂ , L₃ = 0

• L₁ = L₃ , L₂ = 0

• L₁ > L₂ > L₃

A current I= 5.0 A flows along a thin wire shaped as shown in given figure. The radius of the curved part of the wire is equal to R = 120 mm and the angle 2$\mathrm{\varphi }$ = 90°. Find the magnetic induction of the field at point O.

• 4.2 × 10^-4 T

• 8.8 × 10^-5 T

• 2.8 × 10^-4 T

• 4.2 × 10^-3 T

A small piece of metal wire is dragged across the gap between the poles of a magnet in 0.4 s. If change in magnetic flux in the wire is 8 x 10^-4 Wb, then emf induced in the wire is

• 8 × 10^-3 V

• 6 × 10^-3 V

• 4 × 10^-3 V

• 2 × 10^-3 V

The magnetic flux linked with a coil at any instant t is given by the equation : $\mathrm{\varphi }$ = 5t³ − 100t + 300. The magnitude of emf induced in the coil after 3 s is

• 10 V

• 20 V

• 35 V

• 70 V

In 0.1 s, the current in a coil increases from 1 A to 1.5 A. If inductance of coil is 60 mH, then induced current in external resistance of 3Ω will be

• 1 A

• 0.5 A

• 0.2 A

• 0.1 A

138.

If a coil of 40 turns and area 4.0 cm² is suddenly removed from a magnetic field, it is observed that a charge of 2.0 x 10^-4 C flows into the coil. If the resistance of the coil is 80 Ω, the magnetic flux density in Wb/m² is

• 0.5

• 1.0

• 1.5

• 2.0

The magnetic flux linked with the coil varies with time as  $\mathrm{\varphi }$ = 3 t² + 4 t + 9. The magnitude of the induced emf at 2 s is

• 9 V

• 16 V

• 3 V

• 4 V

A coil having an inductance of 0.5 H carries a current which is uniformly varying from 0 to 10 A in 2s. The emf (in volts) generated in the coil is

• 10

• 5

• 2.5

• 1.25