REVISION ASSIGNMENT PHYSICS (CLASS XII) UNIT 4 4-- ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT 1. Predict the polarity of the capacitor C connected to coil, which is situated between two bar magnets moving as shown in figure. 2. If the number of turns in the solenoid is doubled, keeping other factors constant, how does the self-inductance of the coil change? 3. A plot of magnetic flux (Ф) versus current (I) for two inductors A and B is as shown in the figure below. Which of the two has large value of self-inductance? 4. A bar magnet falls through a ring of wire having a cut, so as not to form a closed loop. Will the acceleration of magnet be equal to the acceleration due to gravity? State the reason. 5. Graduations on scale in ac ammeter and voltmeter are not equally distant, why? 6. A bar magnet m is dropped so that it falls vertically through the coil C. The graph obtained for voltage produced across the coil versus time is showing in figure (b). 7. A radio can tune over the frequency range of a portion of medium wave (MW) broadcast band (800 kHz to 1200 kHz). If its LC circuit has an effective inductance of 200µH, what must be the range of variable capacitor? 8. A small piece of metal wire is dragged across the gap between the pole piece of a magnet in 0.5 s. The magnetic flux between the pole pieces is known to be 8 x 10-4 Wb. Estimate the induced emf in the wire. 9. A resistor of 200Ω and a capacitor of 15.0 µ F are connected in series to a 220 V, 50Hz ac source. Calculate the current in the circuit and the rms voltage across the resistor and the capacitor. Is the algebraic sum of these voltages more than the source voltage? If yes, resolve the paradox. 10. Current in a circuit falls steadily from 5.0 A to 0.0 A in 100ms. If an average emf of 200 V is induced, calculate the self inductance of the circuit.