Download Current Electricity Problems

Current Electricity Problems
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1. A capacitor that is connected to a 45 V source contains 90 microCoulombs of charge. What is the
capacitor’s capacitance?
2. A 5.4 microFarad capacitor is charged with 3.4 milliCoulombs. What potential difference exists across
it?
3. A 62 picoFarad capacitor is charged when it has 50 microCoulombs of charge on it. What size voltage
source is it connected to it?
4. What is the charge in a 15 picoFarad capacitor when it is connected across a 75 V source?
5. A 10 microFarad capacitor is charged to 300 V. How much energy is stored?
6. A 50 picoFarad capacitor is connected to a 9 V battery, how much energy is stored in the capacitor?
Material
aluminum
copper
german silver
nickel silver
iron
Table 1: Resistivity (Temperature - 20°C)
Resistivity (x 10-6 Ω•cm)
2.824
1.724
33
49
10
Table 2: Properties of Wire (Temperature - 20°C)
American Wire Gauge (B & S) for any metal
Gauge Number
Diameter (mm)
Cross Sectional Area (mm2 )
18
1.024
0.8231
20
0.8118
0.5176
24
0.5106
0.2047
28
0.3211
0.08098
30
0.2546
0.05093
7.
What is the resistance of a copper wire 20 m long and 0.81 mm in diameter at 20°C?
8. At 20°C, 100 m of No. 18 gauge copper wire has a resistance of 2.059 Ω. What is the resistance of 500
m of this wire?
9. The diameter of the copper wire in Problem 8 is 1.024 mm. What is the resistance of 100 m of No. 30
gauge copper wire, which has a diameter of 0.2546 mm?
10. What is the resistance of 125 m of No. 20 gauge aluminum wire at 20°C?
11. No. 24 gauge German silver wire has a diameter of 0.511 mm at 20°C. How many centimeters are
needed t make a resistance spool of 100 Ω?
12. A resistance of 60 Ohms has a current of 0.4 A through it when it is connected to the terminals of a
battery. What is the voltage of the battery?
13. A 20 Ohm resistor is connected to a 30 V battery. What is the current in the resistor?
14. A 12 V battery is connected to a device and 24 mA of current flows through it. If the device obeys
Ohm’s law, how much current will flow when a 24 V battery is used?
15. A lamp draws a 66 mA current when connected to a 6 V battery. When a 9 V battery is used, the lamp
draws 75 mA. Does the lamp obey Ohm’s Law? Is it Ohmic or Non-Ohmic? How much power does
the lamp dissipate at 6 V? How much power does it dissipate at 9 V?
16. The current through a lamp connected across 120V is 0.4 A when the lamp is on. What is its resistance
when it is on? When the lamp is cold, its resistance is one fifth as large as when the lamp is hot. What
is its cold resistance? What is the current through the lamp as it is turned on if it is connected to a
potential difference of 120 V?
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17. What is the maximum current that should be allowed in a 5 W, 220 Ohm resistor?
18. The wire in a house circuit is rated at 15 A that has a resistance of 0.15 Ohms. What is the power
rating? How much heat does the wire give off in 10 minutes?
19. A current of 1.2 A flows through a 50 Ohm resistor for 5 minutes. How much heat was generated by the
resistor?
20. A 6 Ohm resistor is connected to a 15 V battery. What is the current in the circuit? How much thermal
energy is produced in 10 minutes?
21. A 110 V electric iron draws 3 A of current. How much heat is developed per hour?
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22. A transistor radio operated by means of a 9 V battery that supplies it with a 50 mA current. If the cost of
the battery is $0.90 and it lasts for 300 hours, what is the cost per kilowatt hour to operate the radio?
23. An electric heater is rated at 500 W. How much energy is delivered to the heater in half an hour? At
$0.08 per kilowatt hour, what does it cost to run the heater 6 hours per day for 30 days?
24. The evening we were trying to observe stars at Jesse Jones Park was not very good due to very high
humidity creating dew on the surface of the telescope. A dew heater can be constructed by connecting
six 25 ohm resistors in series in the shape of a ring to fit inside the rim of the telescope. If the ring of
resistors is connected to a 12VDC source what is the current flow and power generated?