Homework 2, Natural ResponseEE 280: Fundamentals of Electric Circuits

College of Engineering, Forestry, & Natural Sciences

Northern Arizona University

Spring 2011

Due Date: Thursday, February 3

Problem 7.17: The 240 V, 2Ω source in the circuit in Fig. P7.17 is inadvertently short-circuited at its terminals

a, b. At the time the fault occurs, the circuit has been in operation for a long time.

+−

10Ω

2mH 6mH

15Ω

a

b

2Ω

240V

Figure P7.17

a) What is the initial value of the current iab in the short-circuit connection between terminals a, b?

b) What is the final value of the current ia,b?

c) How many microseconds after the short circuit has occured is the current in the short equal to 114 A?

EE280, Spring 2011, Homework 2 1

Problem 7.32: At the time the switch is closed in the circuit shown in Fig. P7.32, the capacitors are charged as

shown.

2µF 1µF

6µF

30V

5V v0v1

v2

+

++

-

-

-++

-

-250kΩ

a) Find v0(t) for t ≥ 0+.

b) What percentage of the total energy initially stored in the three capacitors is dissipated in the 250kΩ resistor?

c) Find v1(t) for t ≥ 0.

d) Find v2(t) for t ≥ 0.

e) Find the energy (in millijoules) trapped in the ideal capacitors.

EE280, Spring 2011, Homework 2 2