91.

A coil of inductance 8 μH is connected to a capacitor of capacitance 0.02 μF To what wavelength is this circuit tuned?

• 7.54 × 10³ m

• 4.12 × 10² m

• 15.90 × 10³ m

• 7.54 × 10² m

Assertion:  An emf E is induced in a closed loop when magnetic flux is varied. The induced electric field E is not a conservative field.

Reason:  The line integral $\oint \overline{\mathrm{E}} · \overline{\mathrm{dl}}$  around the closed loop is non-zero.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

The most suitable metal for making electromagnets and transformer cores is

• steel

• iron

• copper

• aluminium

Which of the following is the best method to reduce eddy currents?

• Laminating core

• Using thick wires

• Reducing hysteresis loss

• None of these

Two solenoids of equal number of turns having their length and the radii in the same ratio 1:2. The ratio of their self-inductance will be

• 1:2

• 2:1

• 1:1

• 1:4

An engine has an efficiency of 1/6. When the temperature of sink is reduced by 62^oC, its efficiency is doubled. The temperature of source will be

• 37^o C

• 62^o C

• 99^o C

• 124^o C

Mutual inductance M between two concentric coils of radii 1 m and 2 m is

• $\frac{{\mathrm{\mu }}_0 \mathrm{\pi }}{2}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{\pi }}{4}$

• $\frac{{\mathrm{\mu }}_{0 }\mathrm{\pi }}{8}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{\pi }}{10}$

Lenz law is consistent with conservation of

• Energy

• Mass

• Charge

• Momentum

A circular coil with a cross-sectional area of  4 cm²  has 10  turns. It is placed at the center of a long solenoid that has 15 turns/cm and a cross-sectional area of IO cm2, as shown in the figure. The axis of the coil conicides with the axis of the solenoid. What is their mutual inductance?

• 7.54 μH

• 8.54 μH

• 9.54 μH

• 10.54 μH

The core of any transformer is laminated so as to

• reduce the energy loss due to eddy currents

• make it light weight

• make it robust &  strong

• D.C ammeter will get damaged