ANSWERS QUIZ 18

Quiz 18   Conceptual Questions (CQ): 7, 8, 9 Problems: 1, 2, 7, 8, 10, 13, 14, 16, 21, 26, 27, 30, 35, 38, 39, 41

ANSWERS TO CONCEPTUAL QUESTIONS:

7. We assume  the voltage in both cases is the same. Then if the resistance grows, the power delivered to the heater will get smaller according to P = V2 / R . If  power decreases, the heating process does slow down.  8. Resistance is given by R = (resistivity)*L/A. Thus, to minimize R,  you should have a small length L with  large cross-sectional area A. Likewise, to maximize R, you should have a large length L with small cross-sectional area A.  (a) For the smallest resistance, connect the wires to  faces with dimensions  "2a by 3a",  maximizing the area (6a2) and minimizing the length (a).  (b) For the largest resistance, connect the wires to faces with dimensions  "a by 2a",  minimizing  area (2a2) and maximizing  length (3a).  9. The statement "P = V2 / R indicates a decrease in power as resistance increases" infers  constant voltage. Statement "P =  I2*R indicates an increase in power as resistance increases" infers  constant current.  Only one of these is true in a given circumstance:  If  resistance changes with constant voltage,  current  also changes;  if  resistance changes with  constant current,  voltage  also changes.

EVEN PROBLEMS ANSWERS:  2, 8, 10, 14,16, 26, 30, 38

2. 1.2X105 C

8. 2.1x1021 electrons/min

10. (a) 5.5 (A)   (b)  7.6 (A)

14. ratio = 1.2

16. Rshort = 2.0 ohms and Rlong = 8.0 ohms.

26. 17 ohms

30. (a) 0.96 (A)  (b) 120 ohms

38. 16 (W)