Voltage across every resistor:

A 120 V battery is linked in series along with three resistors: 40Ω, 60Ω, and 100Ω in the Figure. Find out the voltage across every resistor.

Figure: Example 2 Series Circuit

Solution:

Step 1: Find total resistance.

R_T = R₁ + R₂ + R₃

R_T = 40 Ω+ 60 Ω+ 100 Ω

R_T = 200 ohms

Step 2: Find circuit current (I).

V_T = IR_T

Solving for I:

I=V_T/R_T

I= 120 volts/200Ω

I= 0.6 amps

Step 3: Find out the voltage across every component.

V₁  = IR₁

V₁  = (0.6 amps)(40 Ω)

V₁  = 24 volts

V₂  = IR₂

V₂  = (0.6 amps)(60 Ω )

V₂  = 36 volts

V₃  = IR₃

V₃  = (0.6 amps)(100 Ω )

V₃  = 60 volts

The voltages of V₁, V₂, and V₃ in Example 2 are called as "voltage drops" or "IR drops."  Their effect is to decrease the available voltage to be applied across the other circuit components.  A sum of the voltage drops in many series circuits is always equal to the applied voltage.  We could verify our answer in Example 2 through using equation (2-4).

V_T =V₁ +V₂ + V₃       

120 volts =  24 volts+ 36 volts+60 volts

120 volts =  120 volts