Question

1- A charged capacitor and an inductor are connected at time t=0. After three and a quarter periods of the resulting oscillations, which of the following quantities reaches its maximum? A. EMF on the inductor B. Magnetic energy C. magnetic flux through the inductor D. None of the above

2- A 1 H superconducting inductor in an oscillating LC circuit with angular frequency 1000 s-1 holds a maximum voltage on a capacitor 1000 V. The maximum current through the inductor is: A. 1 A A. 0.04 F B. 120 V C. Zero D. None of the above

3-A 1000 turns solenoid, 1 m long and 1 cm in diameter, carries a current of 500 A. The magnetic flux through a cross-section of the solenoid is : A. 50 μWb B. 1 Wb C. 471 T D. 29 H E. None of the above

4- The inductance of a closely packed coil of 400 turns per meter is 8.0 mH. Calculate the magnetic moment of the coil when the current is 5.0 mA. 0.08 Am2 0.1 Wb 0.1 N/m None of the above

Answer 1

Solution

1) B. Magnetic energy and C. Magnetic flux through inductor.

See the figure describing current and charge on the capacitor in the LC circuit.,

T is the period of oscillation. We can see that the current peaks at T/4 (quarter of time period). Thus magnetic energy and magnetic flux which depends on the current through the solenoid will also peak at quarter the time period point.

2) A. 1A (see attached for calculation)

3) A. 50uWb

4) A. 0.08 Am^2