Practice Problems: A Review of Basic Circuit Analysis
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1. (easy) Explain, using the concepts discussed in the previous lecture, how the drift velocity of charges in a circuit is small in comparison to the speed of the signal that causes them to move.
2. (moderate) If 5x1016 electrons pass a point in a conductor every 2 ms, find the current in the conductor. (Recall that each electron has a charge of 1.6x10-19C)
3. (moderate) How much time must pass for an electron to travel 0.85 m in a copper conductor whose cross sectional area is 0.21 cm2 if the current in the wire is 300 A? Use the n value for copper as n = 8.47x1028 electrons/m3.
4. (easy) A piece of iron is shaped as a block with a length of 0.15 m, a width of 0.012 m and a depth of 0.012 m. If the the resistivity of iron is 9.7x10-8 Ωm, find the resistance of this object along its length? Does the resistance change if measured along its depth. If so, why?
5. (moderate) If a conducting wire (X) has a resistance of Rx, determine the resistance of a second wire (Y) if the resistivity is twice the resistivity of X, but is only half as long and has three times the diameter.
6. (easy) A resistor is connected to a 20 v emf. The current through the resistor is found to be 2A. What current would move through the resistor if it was connected to a 50 v source? Find the rate at which the energy is dissipated by the resistor with the 50 v source.
7. (easy) Explain why the sketch shown below is a good analogy for Ohm's Law.
8. (easy) Determine the current in a circuit that contains a 10 volt emf and 3 Ohmic resistors in series. Ohmic resistors are resistors that obey Ohm's Law. (Non-Ohmic do not obey Ohm's Law). The banded resistance on the resistors are as follows:
Resistor #1: Green|Yellow|Red|Gold
Resistor #2: Blue|Red|Brown|Gold
Resistor #3: Red|Red|Red|Silver
9. (moderate) Estimate the cost of cooking a turkey for 4 hours in an oven that operates at 20 A and 240 v. Assume the cost for 1.0 kwh is 8 cents.
10. (moderate) A heating element in a kitchen appliance uses a voltage of 120 volts. The device dissipates 10000 J of energy in 10 seconds. Find both the resistance of the heating element and the current that is established.
11. (moderate) A certain toaster has a heating element made of nichrome wire. When first connected to a 120 v emf the wire is at 20°C and the initial current is 1.8 A. When the toaster reaches its final operating temperature the current in the nichrome wire is 1.53 A. Determine the power consumed at the final temperature and the final temperature itself. Note: The resistivity changes with temperature according to this equation: ρ = ρo(1 + 0.0004(Tf - 20)).
(Also, assume that the size of the wire doesn't change due to thermal expansion)
12. (easy) A 3 volt battery is connected to two identical resistors (R = 10 Ω). First, determine the current from the battery if the resistors are connected in series and then find the current if the resistors are connected in parallel.
13. (moderate) Determine the power dissipated by each resistor in problem #12. What is the total power in each case?
14. (easy) Three identical resistors (R) are connected to a battery in a simple circuit. Of those listed below, which equivalent resistances can the circuit exhibit?
R/3, 3R/2, 5R/2, R/2
15. (moderate) A 10 volt battery, a 60 Ω resistor, a light bulb and a fuse (R = 0.02 Ω) are connected in series. The light bulb dissipates 100 watts when connected across a 20 v source. If the fuse is rated at 0.1 A, will the circuit operate?
16. (moderate) If the 60 Ω resistor in the previous question was replaced with a larger resistor, what would its minimum resistance be so that the circuit would operate? Find the minimum value for the total resistance when the current is 0.1 A.
17. (moderate) Analyze the circuit below in order to fill in the chart.
18. (moderate) A teacher challenges a group of students to create a circuit that costs $1.00 to operate over two days. The cost per kwh is $0.20 in the lab. The students must use 4 identical lightbulbs (not all in series) in the circuit and a 20 v battery.
a. Design a circuit that would allow the students to meet the challenge. You must report the resistance of the lightbulbs you choose to use.
b. If all the bulbs determined in part (a) were used in series, would the current from the battery increase or decrease and would the cost to operate the circuit over two days increase or decrease? Explain your answer.
19. (moderate) Find the voltage across and the current through 330Ω resistor and the middle 560Ω resistor in the circuit shown below. 
Please supplement these problems with those found in your companion text.