Series & Parallel Circuits
There are two ways of joining electrical components, in series and in parallel. Some circuits include both series and parallel parts.
- There is the same current through each component
- The total potential difference of the power supply is shared between the components
- The total resistance of two components is the sum of the resistance of each component. Rtotal = R1 + R2
- The total current through the whole circuit is the sum of the currents through the separate components
- The potential difference across each component is the same
- The total resistance of two resistors is less than the resistance of the smallest individual resistor.
The more resistors in series you have, the greater the overall resistance.
Adding resistors in parallel decreases the total resistance because there are more paths for the current to flow through.
Question: Look at Figure 2. Explain how the potential difference across the resistor and the lamp will change when the switch is closed. (4 marks)
the potential difference across the resistor becomes 0V
because there is a short circuit across the resistor
the potential difference across the lamp increases
because the current increases
Solving problems for circuits which include resistors in series using the concept of equivalent resistance:
Question: Compare the currents I1, I2 and I3 in Figure 2
I1 = I2 + I3
I2 = I3
I1 = 2I2
I1 = 2I3
Question: What is the combined resistance of each pair of resistors in Figure 3?
P: 10 + 10 = 20 Ohms
Q: Less than 10 Ohms
R: 5 + 5 = 10 Ohms
S: Less than 5 Ohms