PHY 112 - Third Hourly Exam – Winter 2000 – Version B

1-3. A parallel plate capacitor consists of two plates, each measuring 50 cm X 40 cm, that are separated from one another by a distance of 0.1 cm. The space between the plates is filled with air and a 6 V battery is connected between the plates.

1. The capacitance is ______ F.

a) 1.77 x 10-9 b) 8.85 x 10-12 c) 1.77 X 10-6 d) 3.54 x 10-10 e) 4.43 x 10-17

2. A dielectric material with a dielectric constant of 3 is inserted between the plates of the capacitor with the 6 V battery still connected. A little later you notice that the

a) capacitance did not change.

b) electric field between the plates increased.

c) charge on either of the plates increased.

d) voltage between the plates decreased.

e) energy stored in the capacitor decreased.

3. When the 6 V battery is replaced with a 12 V battery, the capacitance becomes ______ times its former value. (This is a trick question.)

a) 4 b) 1/4 c) 2 d) 1 e) 1/2

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4. An ampere is the same as a

a) coulomb/sec b) N/coulomb c) ohm/m d) volt/sec e) volt/m

5. You wish to replace a 2.5 W piece of copper wire with a 5 W piece of copper wire. For the replacement you select a piece of copper wire with

a) twice the resistivity.

b) half the length and the same diameter.

c) the same diameter and twice the length.

d) twice the length and half the diameter.

e) the same length and half the diameter.

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6-9. A hair dryer is rated at 1000 W when plugged into a 120V-60Hz outlet.

6. The rms current when it is turned on is _____ A.

a) 12 b) 14.1 c) 8.3 d) 16.7 e) 5.9

7. The resistance of the hair dryer filament is _____ W .

a) 28.7 b) 14.4 c) 3.60 d) 5.00 e) 6.94

8. The maximum voltage applied to the hair dryer is _____ V.

a) 60 b) 170 c) 240 d) 84.9 e) 120

9. The peak power it dissipates is _____ W.

a) 707. b) 2000 c) 1414 d) 1000 e) 500

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 10. Friday is March 17 and many of us will be wearing green clothing and hats and drinking green beverages because Friday is _____ Day.

a) Spring b) St. Valentine's c) Einstein's d) Physics is Phun e) St. Patrick's

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11-14. A 6 volt battery with an internal resistance of 2 W is connected to a circuit as shown in Figure 2. The current in the 5 W resistance is 0.439 A and the current in the 10 W resistance is 0.293 A.

11. The current in the 20 W resistance is _____ A.

a) 0.098 b) 0.293 c) 0.586 d) 0.439 e) 0.146

12. The voltage across the 20 W resistance is _____ V.

a) 2.92 b) 0.98 c) 5.84 d) 4.39 e) 1.46

13. The equivalent resistance of the three resistance combination connected between points "a" and "b" is _____ W .

a) 30.5 b) 35.0 c) 5.15 d) 2.86 e) 11.7

14. The terminal potential difference across the battery, Va-Vb = _____ V.

a) 6.88 b) 5.12 c) 6.00 d) 2.64 e) 0.88

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15. When resistances are connected in series the _____ is always the same for each.

a) resistivity b) current c) voltage drop d) power dissipated e) resistance

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16. In Figure 1, the current in the 24 W resistance is

a) 1/8 A b) 3/4 A c) 1/2 A d) 0 A e) 1/4 A

17. In Figure 1, the current in the upper 12 W resistance is

a) 0 A b) 1 A c) 1/8 A d) 1/4 A e) 1/2 A

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18-19. An uncharged 50 x 10-6 F capacitor, a 5000 W resistance, and a 12 volt battery are connected in series to form a closed loop.

18. As soon as the loop is closed, the voltage across the capacitor is _____ V.

a) 0 b) 6 c) 12 d) 7.6 e) 4.4

19. The voltage across the capacitor 0.25 s after the loop is closed is _____ V.

a) 6 b) 12 c) 4.4 d) 0 e) 7.6

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20. Two 30 x 10-6 F capacitors are connected in series with one another and the combination is connected between the terminals of a 1.5 V battery. The charge on the capacitor plate closest to the positive terminal of the battery is _____ x 10-6 C.