Example 18.1: Four Resistors in Series
Problem: Four resistors are arranged as shown in Figure 18.5a, where R1 = 1.0 Ģ, R2 = 2.0 Ģ, R3 = 2.5 Ģ, and R4 = 3.5 Ģ. Find (a) the equivalent resistance of the circuit and (b) the current in the circuit if the emf of the battery is 6.0 V.
Strategy: Because the resistors are connected in series, summing their resistances gives the equivalent resistance. Ohm's law can be used to find the current.
Solution:
(a) Find the equivalent resistance of the circuit.
Apply Equation 18.4, summing the resistances:
Req = R1 + R2 + R3 + R4 = 1.0 Ģ + 2.0 Ģ + 2.5 Ģ + 3.5 Ģ
(b) Find the current in the circuit.
Apply Ohm's law to the equivalent resistor in Figure 18.5b, solving for the current:
I = ĪV/Req = V/Req