When power is drawn from the secondary coil of the transformer, the dynamic resistance

• increases

• decreases

• remains unchanged

• changes erratically

The magnetic flux linked with a coil at any instant t is given by the equation $\mathrm{\varphi } = 5{\mathrm{t}}^3 - 100 \mathrm{t} + 300$. The magitude of emf induced in 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 1.5A. If inductance of coil is 60 mH, then induced current in external resistance of 32 will be

• 1 A

• 0.5 A

• 0.2 A

• 0.1 A

In 0.2 s, the current in a coil increases from 2.0 A to 3.0 A. If inductance of coil is 60 mH, then induced current in external resistance of 3 Ω will be

• 1A

• 0.5 A

• 0.2 A

• 0.1 A

A transformer having efficiency of 75 % is working on 220 V and 4.4 kW power supply. If the current in the secondary coil is 5 A. What will be the voltage across secondary coil and the current in primary coil?

• V_s = 220 V, i_p = 20A

• V_s = 660 V, i_p = 15 A

• V_s = 660 V, i_p = 20 A

• V_s = 220 V, i_p = 15 A

A cylinder of radius R and length L is placed in a uniform electric field E parallel to the cylinder axis. The total flux for the surface of the cylinder is given by

• 2πR² E

• π R²/E

• R / E

• Zero

In the given figure what will be the coefficient of mutual inductance

88.

The total charge induced in a conducting loop when it is moved in magnetic field depends on

• the rate of change of magnetic flux

• initial magnetic flux only

• the total change in magnetic flux

• final magnetic flux only

For MRI, a patient is slowly pushed in a time of 10 s within the coils of the magnet where magnetic field is B = 2.0 T. If the patient's trunk is 0.8 m in circumference, the induced emf around the patient's trunk is

• 10.18 x 10^-2 V

• 9.66 × 10² V

• 10.18 × 10^-3 V

• 1.51 × 10^-2 V

The self-inductance of a coil having 400 turns is 10 mH. The magnetic flux through the cross-section of the coil corresponding to current 2 mA is

• 2 × 10^-5 Wb

• 2 × 10^-3 Wb

• 3 × 10^-5 Wb

• 8 × 10^-3 Wb