Page 363 - Schaum's Outline of Theory and Problems of Applied Physics

348 ELECTROMAGNETIC INDUCTION [CHAP. 28

28.18. A potential difference of 100 V is applied to a 50-mH, 40- inductor. (a) What is the initial rate at which the current
increases? (b) What is the rate at which the current is increasing when I = 1A?(c) What is the final current?

28.19. A potential difference of 50 V is applied across a 12-mH, 8- inductor. (a) What is the initial rate at which the
current increases? (b) What is the current when the rate of change of current is 2000 A/s? (c) What is the final
current?

28.20. What is the time constant of a 50-mH, 3- inductor?
28.21. A 60-mH, 5- inductor is connected to a 12-V battery whose internal resistance is 1 .(a) Find the time constant
of the circuit. (b) Find the final current in the circuit. (c) Find the current 0.005, 0.01, and 0.05 s after the connection
is made.

28.22. Find the current in the above inductor 0.005, 0.01, and 0.05 s after it has been short-circuited, after having been
connected to the battery for a long time.

28.23. A 0.1-H, 4- inductor is connected in series with a 0.2-H, 6- inductor, and the combination is placed across a
24-V battery whose internal resistance is 2 .(a) Find the time constant of the circuit. (b) Find the final current in
the circuit. (c) Find the current at 0.01 and 0.1 s after the connection is made.
28.24. Find the current in the inductors of Prob. 28.23 at 0.01 and 0.1 s after the battery has been short-circuited, after the
inductors have been connected to it for a long time.

Answers to Multiple-Choice Questions

28.1. (a), (c), (d) 28.8. (a)
28.2. (a) 28.9. (c)

28.3. (b) 28.10. (b)

28.4. (a), (b), (d) 28.11. (a)

28.5. (c) 28.12. (d)

28.6. (b) 28.13. (a)
28.7. (b) 28.14. (c)

Answers to Supplementary Problems

28.1. When the connection is made, there will be a momentary current in the secondary winding as the current in the
primary builds to its final value. Afterward, since the primary current will be constant and hence its magnetic field
will not change, there will be no current in the secondary.
28.2. The changing magnetic field produced by an alternating current in the primary winding

28.3. From their definitions L = V t/I and R = V/I. Hence L/R = (V t/I)/(V/I) = t.

28.4. 100 m/s