AQA GCSE Series Circuit Calculations(Physics)

Equation for potential difference, current and resistance

Example 1

Calculating current in a series circuit

In the circuit above calculate the current,I  flowing in the circuit.

V = IR, 

So, I = V/R

I = 6/2 = 3A

Example 2

Calculating resistance in a series circuit

 In the circuit above calculate the resistance  of the resistor on the right.

First we need to find the total resistance of the whole circuit, using the potential difference across cell and reading on ammeter.

V = IR

R = V/I, R = 6/2 = 3 ohms

In a series circuit, total resistance is the sum of the individual resistors. So, if the total resistance is 3 ohms and the resistor on the left is 0.8 ohms, then the resistor on the right is 3-0.8 = 2.2 ohms.

Example 3

In the circuit above calculate V1 and R1

In a series circuit the potential difference is shared between the components. So 15V = 5V + V1. Therefore, V1 = 10V.

We can now work out the current flowing through the 50 ohm resistor, using V = IR

I = V/R, I = 10/50 = 0.2A

In a series circuit, current is the same at all points. This means that a 0.2A current will also flow through R1.

V = IR, so R1 = V/I

R1 = 5/0.2 = 25 ohms

Practice Questions

1.Calculate the resistance of the bulb in the circuit below

Calculating resistance in a series circuit

2. Calculate the current flowing through the circuit below with the two resistors.  

Calculating current in a series circuit

3. In the circuit below, calculate V1 and R1

Calculating resistance in a series circuit