# Electronics for Absolute Beginners, Chapter 3

## Step 5: Series Circuit 5

We mentioned that in a series circuit, voltage drops are additive. A voltage drop is a voltage that is dropped across a resistor. When the resistor has a higher resistance, the voltage drop across that resistor is also higher. When the resistor has a smaller resistance, the voltage drop across that resistor is also smaller.

The voltage drop of across a resistor (VR) can be calculated by multiplying the resistor by the total voltage (VT) and dividing the result by the total resistance (RT).
VR = (R x VT) / RT

Exercise 4: A circuit with a total voltage of 12V and three resistors 5k Ω, 10k Ω, 1k Ω respectively. Find the voltage drop across the first resistor (VR1), the voltage drop across the second resistor (VR2), and the voltage drop across the third resistor (VR3).

RT = R1+R2+R3
RT = 5000 + 10000 + 1000
RT = 16000
RT = 16k Ω

VR1 = (R1 x VT) / RT
VR1 = (5000 x 12) / 16000
VR1 = 60000 / 16000
VR1 = 3.75V

VR2 = (R2 x VT) / RT
VR2 = (10000 x 12) / 16000
VR2 = 120000 / 16000
VR2 = 7.5V

VR3 = (R3 x VT) / RT
VR3 = (1000 x 12) / 16000
VR3 = 12000 / 16000
VR3 = .75 or 750mV

Most importantly, when we add all of the voltage drops together, we can find the total voltage VT.

VT = VR1+VR2+VR3
VT = 3.75 + 7.5 + .75
VT = 12V
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