🧮 VOLTAGE DIVIDER CALCULATIONS

What are the three steps for calculating voltage across a resistor in a series circuit?

Step 1

Calculate total resistance:

Rtotal​=R1​+R2​+…

Step 2

Calculate total current:

I = Rtotal​/Vtotal

​​Step 3

Calculate voltage across the chosen resistor:

Vx​=I×Rx​

Two 3 Ω resistors are connected to a 6 V supply. What is the total resistance?

R_T​ =3+3

R_T​ =6Ω​

If the total resistance is 6 Ω and the supply is 6 V, what is the current?

I=R/V​

I=6/6

​I=1A​

What voltage is across a 3 Ω resistor when 1 A flows through it?

V = IR

V = 1×3

V = 3V

A 6 V battery is connected to a 3 Ω and 9 Ω resistor in series. What is the total resistance?

RT​ = 3+9

12Ω

What current flows through the 3 Ω + 9 Ω series circuit connected to 6 V?

I=6/12

​I=0.5A

What voltage is across the 9 Ω resistor?

V=IR

V=0.5×9

V=4.5V​

What voltage is across the 3 Ω resistor in that same circuit?

V=0.5×3

3V​

Check:

3 V + 4.5 V ≠ 6 V

This reveals that the values in the supplied example are internally inconsistent. If the circuit is 3 Ω + 9 Ω connected to 6 V, the voltage drops must be:

• 3 Ω → 1.5 V

• 9 Ω → 4.5 V

because:

0.5×3=1.5V

So don't memorise the corrupted “3 V” value from the notes.