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# Electrical Current Practice Questions

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Updated on Sep 27, 2011

Review these concepts at: Electrical Current Study Guide

## Practice Questions

1. Consider the previous example. If the same number of electrons speed up and pass through the same cross-sectional area in a nanosecond (nano = 10–9), what happens to the electrical current? Show calculations.
2. What happens to the current if the particles moving through the conductor are positive ions with the same absolute value of the charge as electrons?
1. Two wires are made of the same material and both have a cross-sectional area A. One has a length L, and the other is three times longer. How do the resistances of the wires compare? Show calculations.
2. Two wires are made of the same material and both have a length L and circular cross-sectional areas. One has a diameter 2.5 times larger than the other. How do the resistances of the wires compare? Show calculations.
3. One 1.5-volt battery is connected to an aluminum (Al) wire and another to an iron (Fe) wire. The two wires have the same length but the Al has a cross-sectional area of the Fe wire. Calculate the ratio of the currents through the two wires.
1. The capacitance of a capacitor free of dielectric is 1.2 pF, and the capacitor is connected to a 9-volt battery. Find the charge on the capacitor's plates.
2. The space between the plates of the capacitor is filled with paper. Find the new capacitance as well as the new charge the plates can store if the battery voltage is kept the same.
1. Consider the diagram in Figure 14.9 of part of a complex circuit. Find the value of the missing current.
2. I1 = 2.25 mA I2 = 8.32 mA I3 = 5.53 mA

I'1 = 3.30 mA I'2= 0.58 mA I'4= 6.50 mA

3. In providing current for a few electrical devices, the battery and the resistors are connected as shown in Figure 14.10. Find the voltage of the battery so that the currents can be supplied as noted in the diagram. Find results to three significant figures.
4. In the previous practice problem, find the current passing through each of the four electrical conductors. Find results to three significant figures.
5. In the previous practice problem, find the voltage drop on each of the four conductors. Find results to three significant figures .
1. Show that for three resistors connected in series and then in parallel, the equation Rs > Rp stands true. The resistors are 20, 30, and 50 ohms.
2. In the circuit shown in Figure 14.13, find the equivalent resistance of the circuit if the resistors are R1 = R5 = 20 Ω, R2 = R4 = 30 Ω, and R3 =50Ω
3. .

4. In the previous practice problem, find the current I if the battery supplies maximum voltage of 12 V.
5. In practice problem 13, find the currents I1, I2, and I3.
6. In practice problem 13, find the voltage drop on each resistor.

1. Decreases to –1.6 · 10–2 A
2. Reverses but absolute magnitude will be the same
3. The longer one has a resistance three times longer.
4. The one with the larger diameter has a resistance of (2.5)2 = 6.25 times smaller.
5. IAl/IFe = RFe/RAl = 1/3
6. 10.8 pC
7. The capacitance increases by three and so does the charge: C = 3.6 pF and q = 32.4 pC.
8. 5.72 mA
9. A voltage of 645 mV has to be supplied.
10. Through resistances R1 and R2, the current is 1.69 mA; through R3 is 3.31 mA and through R4 is 5 mA.
11. V1 = 37.4 mV, V2 = 109 mV, V3 = 145 mV, V4 = 500mV
12. Rseries = 100Ω, Rparallel = 9.7Ω
13. 59.67Ω ~ 60Ω
14. I = 0.2A
15. I1 = 0.097 A, I2 = 0.064 A, I3 = 0.039 A
16. V1 = V2 = V3 = 2 V, V4 = 6 V, V5 = 4 V

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