Series Circuits

The current flows through each bulb/resistor is the same
I = I1 = I2

The potential difference across each resistor depends directly on its resistance. The potential difference supplied by the dry cells is shared by all the resistors.
V = V1 + V2

where V is the potential difference across the battery

If Ohm’s law is applied separately to each resistor, we get :
V = V1 + V2
IR = IR1 + IR2

If each term in the equation is divided by I, we get the effective resistance
R = R1 + R2

Worked example :

There are two resistors in the circuit shown. Resistor R1 has a resistance of 1Ω. If a 3V voltage causes a current of 0.5A to flow through the circuit, calculate the resistance of R2.

solution :
V = IR
3=0.5(1+R2)
R2 = 5Ω