If you think that the wire used in the experiment is not resistance-less (i.e. They also need real, hands-on practice building circuits and using test equipment. This activity was created by Steven Gutierrez, Why don’t the calculated figures from the previous paragraph agree with the actual measurement? How much current is Resistors, while simple to study, do not exhibit the behavior of most electronic components. Your students should learn to make graphs as tools for their own understanding of data. This question is little more than drill for students learning how to express quantities in scientific and metric notations. The problem is determine the resistance R and the voltage source V sub s. So we have a current source, on the left-hand side of the circuit that also has a voltage associated with … You will learn much more by actually building and analyzing real circuits, letting your test equipment provide the “answers” instead of a book or another person. The resistance of the heating element is approximately, Concrete Technology and Design of Concrete Structures. The derivative of a linear function is a constant, and in each of these three cases that constant equals the resistor resistance in ohms. From this line, and also from the numerical figures, you should be able to discern a constant ratio between voltage and current. Plot the relationships between voltage and current for resistors of three different values (1 Ω, 2 Ω, and 3 Ω), all on the same graph: What pattern do you see represented by your three plots? The studies of electricity and electronics are rich in mathematical context, so exploit it whenever possible! Unlike a resistor, which offers a relatively fixed (unchanging) amount of resistance to the motion of electrons over a wide range of operating conditions, the electrical resistance of light bulbs typically change dramatically over their respective operating ranges. I = 45 mA, R = 3.0 kΩ; E = 140 V = 1.4 ×102 V, I = 10 kA, R = 0.5 mΩ; E = 5 V = 5 ×100 V, E = 45 V, R = 4.7 kΩ; I = 9.6 mA = 9.6 ×10−3 A, E = 13.8 kV, R = 8.1 kΩ; I = 1.7 A = 1.7 ×100 A, E = 500.0 μV, I = 36 nA; R = 14 kΩ = 1.4 ×104 Ω, E = 14 V, I = 110 A; R = 130 mΩ = 1.3 ×10−1 Ω, I = 0.001 A, R = 922 Ω; E = 900 mV = 9 ×10−1 V, I = 825 A, R = 15.0 mΩ; E = 12.4 V = 1.24 ×101 V, E = 1.2 kV, R = 30 MΩ; I = 40 μA = 4 ×10−5 A, E = 750 mV, R = 86 Ω; I = 8.7 mA = 8.7 ×10−3 A, E = 30.0 V, I = 0.0025 A; R = 12 kΩ = 1.2 ×104 Ω, E = 0.00071 V, I = 3389 A; R = 210 nΩ = 2.1 ×10−7 Ω, Published under the terms and conditions of the Creative Commons Attribution License. Ohm’s Law would suggest an infinite current (current = voltage divided by zero resistance). Resistance: measured in Ohms, is represented by R (or the Greek letter ω) Power: measured in watts, is represented by the letter W; Recommended: Basic Electrical Terms and Defintions. It has been my experience that students require much practice with circuit analysis to become proficient. Let the electrons themselves give you the answers to your own “practice problems”! Since V(Voltage) and Carefully measure those quantities, to verify the accuracy of your analysis. They can’t, but you can. If students have access to either a graphing calculator or computer software capable of drawing 2-dimensional graphs, encourage them to plot the functions using these technological resources. How much current would result, according to Ohm’s Law? If there are any substantial errors (greater than a few percent), carefully check your circuit’s construction against the diagram, then carefully re-calculate the values and re-measure. Apply Ohm’s Law to vertical columns in the table. Yet, the experiment described yields only a modest amount of current. Solve for the unknown quantity (E, I, or R) given the other two, and express your answer in both scientific and metric notations: I = 20 mA, R = 5 kΩ; E = 100 V = 1 ×102 V, I = 150 μA, R = 47 kΩ; E = 7.1 V = 7.1 ×100 V, E = 24 V, R = 3.3 MΩ; I = 7.3 μA = 7.3 ×10−6 A, E = 7.2 kV, R = 900 Ω; I = 8.0 A = 8.0 ×100 A, E = 1.02 mV, I = 40 μA; R = 26 Ω = 2.6 ×101 Ω, E = 3.5 GV, I = 0.76 kA; R = 4.6 MΩ = 4.6 ×106 Ω, I = 0.00035 A, R = 5350 Ω; E = 1.9 V = 1.9 ×100 V, I = 1,710,000 A, R = 0.002 Ω; E = 3.42 kV = 3.42 ×103 V, E = 477 V, R = 0.00500 Ω; I = 95.4 kA = 9.54 ×104 A, E = 0.02 V, R = 992,000 Ω; I = 20 nA = 2 ×10−8 A, E = 150,000 V, I = 233 A; R = 640 Ω = 6.4 ×102 Ω, E = 0.0000084 V, I = 0.011 A; R = 760 μΩ = 7.6 ×10−4 Ω. Comment. A CD player with a resistance of 40 ohms has a This is an example of a linear function: where the plot describing the data set traces a straight line on a graph. First, the voltage/current plot for an incandescent light bulb: Next, the voltage/current plot for a gas-discharge light bulb: Based on these two graphs, what can you say about the electrical resistance of each bulb type over its operating range? But most of us plan for our students to do something in the real world with the education we give them. To what minimum resistance value can the rheostat be set without blowing the fuse?