# Homework Assignment

### Problems: 32.2, 12, 19, 22, 32, 53, 65

Q1, Why is the induced emf that appears in an inductor called a "counter" or "back" emf?

Q4, How can a long piece of wire be wound on a spool so that the wire has a negligible self-inductance?

Q5, A long, fine wire is wound as a solenoid with a self-inductance L. If it is connected across the terminals of a battery, how does the maximum current depend upon L?

Q6, For the series RL circuit shown here, can the back emf ever be greater than the battery emf?

Q7, Suppose the switch in the diagram above has been closed for along time and is suddenly opened. Does the current instantaneously drop to zero? Why does a spark appear at the switch contacts at the instant the switch is thrown open?

Q9, Discuss the similarities between the enrgy store in the electric field of a charged capacitor and the energy stored in the magnetic field of a current-carrying coil.

Q14, In the LC circuit shown in Figre 32.12, the charge on the capacitor is sometime zero, even though there is current in the circuit. How is this possible?

Q16, How can you tell whether an RLC circuit is overdamped or underdamped?

Q17, What is the significance of critical damping in an RLC circuit?

32.2, A spring has a radius of 4.00 cm and an inductance of 125 microHenries when extended to a length of 2.00 m. Find an approximate value for the total number of turns in the spring?

32.12, A solenoid inductor is 30.0 cm long and has a cross-sectional area of 4.00 cm2. When the current through the solenoid decreases at a rate of 0.625 A/s, the induced emf is 200 microVolts. Find the number of turns per unit length of the solenoid.

32.19, Calculate the resistance in an RL circuit in which L = 2.5 H and the current increases to 90% of its final value in 3.0 s.

32.22, An inductor that has an inductance of 15.0 H and a resistance of 30.0 ohms is connected across a 100-V battery. What is the rate of increase of the current

(a) at t = 0 and

(b) at t = 1.50 s?

32.32, Calculate the energy associated with the magnetic field of a 200-turn solenoid in which a current of 1.75 A produces a flux of 3.70 x 10 - 4 Wb in each turn.

32.53, A 1.00 microFarad capacitor is charged by a 40.0-V power supply. The fully charged capacitor is then discharged through a 10.0-mH inductor. Find the maximum current in the resulting oscillations.

32. 65 Consider an LC circuit in which L = 500 mH and C = 0.100 microFarads.

(a) What is the resonant frequency (o)?

(b) If a resistance of 1.00 k is introduced into this circuit, what is the frequency of the (damped) oscillations?

(c) What is the percent difference between the two frequencies?