DC Circuits


The current flowing in a circuit containing four resistors connected in series is I = 1.0 A. The potential drops across the first, second and third resistors are, respectively: V = 5 V, V = 8 V and V = 7 V.
The equivalent resistance of the circuit is R = 30.
Find the total voltage supplied by the battery, and also current, voltage drop, and resistance of each resistor in the circuit.
Figure 1 Example Problem: Resistors in series


  1. How are resistors related when connected in series?
  2. What is true about potential drops of resistors when connected in series?
  3. You will need to use Ohm's Law.

Figure 2 Example Problem, with given data
First, let's label the diagram with the information given in the question.

There are several ways of solving this problem (see alternate solutions), but this tutorial will only go through one of these ways.

Because the resistors are connected in series, then the same current flows through each one. Using the Ohm's Law, we can find the resistances of the first, second and third resistors. Now, using the equivalent resistance, we can find the resistance in the fourth resistor. This is a series circuit, so the equivalent resistance is the sum of the individual resistances. The current flowing through the fourth resistor is also I=1.0A. Using Ohm's Law again, we find the voltage across this resistor. The total voltage supplied by the battery must equal to the total voltage drop across the circuit (this is known as Kirchhoff's Voltage Law). So, we must sum up the voltage drops across the resistors.
Explanation of Resistors in Series
Continue to: Resistors in Parallel
Self Test
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