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Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

The Basic Idea

Charge that flows in a circuit encounters a change in electric potential (or electric pressure) whenever it passes through a resistor such as a bulb or a battery. There is a gain in electric potential within the battery and a loss of electric potential within the resistors (e.g., the bulbs). The loss in electric potential - sometimes referred to as a voltage drop (∆V) - can be calculated from knowledge of the current (I) and the resistance (R). The product I•R is equal to the voltage drop. Knowing the battery voltage and the current and resistance for the bulbs, one can calculate the voltage drops and thus the electric potential for each location in a circuit.
 

The I and R values are given. Use them to determine the electric potential (in volts) at the four indicated positions. If desired, begin by using the ROYGB palette to color code the wires.


 

How to Think About This Situation

The battery has a voltage rating of 24 V. This is the difference in electric potential between the positive and the negative terminal. Since the negative terminal is typically assigned a potential of 0 V, the positive terminal of this battery is 24 V higher in potential. Any wire attached to these terminals shares the same electric potential value as the terminal it is attached to. This allows you to determine the electric potential at locations A and F.  


Charge encounters a voltage drop (or loss of electric potential) as it passes through a bulb. For instance, charge passes through the first bulb as it passes from location A to B. The actual voltage drop value can be calculated as I•R. The I is listed in amps (A) and the R is listed in ohms (Ω),  Multiplying these two values provides knowlege of the amount of voltage drop (∆V). Subtracting this ∆V value from the electric potential value a location A allows you to determine the electric potential value of the wires that location B is one.

There is a second bulb along the top of the diagram. The electric potential of the wire leading into the bulb has been calculated (assuming you followed the directions in the preceeding paragraph). You can determine the electric potential value just after the bulb (which includes location C) by calculating the I•R voltage drop for this bulb. Subtracting this ∆V from the value of electric potential at location B will lead to the value at location C.

Very similar calculations can be performed to determine the electric potential values at locations D and E. A combination of multiplication (I•R) to determine the voltage drop and subtraction to determine the electric potential value just after the bulb will lead to values for locations D and E.

You can easily do a final check of your calculations. A fifth set of I an R values are given for the last bulb located between locations D and F (or E and F). Thus, you can calculate a fifth ∆V value. This ∆V should be equal to the difference in electric potential values between locations D and F (and E and F).

About Color-Coding
This Know Your Potential Concept Builder relies upon the conceptual tool of color-coding wires according to their relative electric potential. While the Volt On It! portion of the Concept Builder does not evaluate your assigned colors for the wires, we recommend that you do the color coding. Color coding the wires enhances your understanding of electric potential and voltage drops.
 


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