Physics 102 Homework #10Due Noon, Tuesday, April 6, 2010

. . . .

Reading:This week: KJF §21.8-21.9, 22, 23.1, 23.3*, 23.6

* In §23.3, we will cover the “series resistors” subsectionthis week and the “parallel resistors” section next week.

Next week: KJF §23, all parts not already covered, except skip §23.7. . . .

Problems: Four problems will be selected at random from among those problems indicatedwith asterisks for grading. You need not to submit solutions to the non-asterisk problems.

Beware: The text problems are a mixture of conceptual questions and problems fromchapters 21, 22, and 23. Be sure to do the correct problems!

1. Two capacitors are constructed from 4 cm×4 cm plates separated by 0.1 mm.Capacitor A has empty space (air) between the plates; capacitor B has a materialwith dielectric constant κ=5. The capacitors are each given potential difference 10V.(a) What is the capacitance of each capacitor?(b) What is the charge on each capacitor? Which has more charge?(c) What is the energy stored in each capacitor? Which stores more energy?

(Answers at end of the assignment.)

2. KJF Problem 21.65.

3. * KJF Problems 21.82 through 21.86.

4. KJF Problem 22.1.

5. * KJF 22.38. (Note: you do not need to know the details of the electrolysis. Thekey point is that every zinc atom added to the sheet requires a charge of 2e to flowthrough the system. You can find the mass of a zinc atom in appendix C of yourtextbook or on any periodic table.)

6. KJF Problem 22.21.

7. KJF Problem 22.45.

8. * KJF Problems 22.40, 22.41, and 22.42. (Note: The potassium atoms, K+, are singlyionized, so they have charge +e.)

9. * KJF Conceptual Question 22.9.

10. (a,b) KJF Problem 23.8.(c) How much current flows around the circuit?

(Answer at end of the assignment.)

11. KJF Problem 23.21. (Reminder: “emf of the battery” means the battery voltage.)

12. * KJF Conceptual Question 23.20.

Continued on the next page....

13. KJF Problem 22.35. (Note: chapter 22, not chapter 23.)

14. KJF Problem 23.25.

15. * Your professor roams the world seeking out homework problems for you. He foundthe hair dryer pictured below in Bangkok two summers ago.(a) What is the resistance of the hair dryer?(b) Are the numbers printed on the hair dryer label consistent with one another? If

so, show that they are consistent. If not, say what is inconsistent.(c) If you were to plug this hair dryer into a 120 V outlet in the United States, how

much power would it consume?Notes: (i) It doesn’t matter that the hair dryer is meant to be plugged into an ACpower source. The formulas we are using work equally well for AC or DC powersources. (ii) Use common sense in interpreting the precision of the numbers given onthe label and the numbers you calculate.

Answers to selected problems:(1) (a)CA =1.4×10−10 F, CB =7.1×10−10 F.

(b)QA =1.4×10−9 C, QB =7.1×10−9 C, capacitor B.(c)EA =7.1×10−9 J, EB =3.5×10−8 J, capacitor B.

(10) (a) 10 Ω resistor: 5 V20 Ω resistor: 10V

(b) Voltage

5V

10V

15V

Position

(c) 0.5 A.