# 2.2.2 Resistors in Series & Parallel

### Resistors in Series

• When two or more resistors are connected in series, the total resistance is equal to the sum of their individual resistances
• For two resistors of resistance R1 and R2, the total resistance can be calculated using: • Where R is the total resistance, in Ohms (Ω)
• Increasing the number of resistors increases the overall resistance, as the charge now has more resistors to pass through Resistors connected in series

#### Worked Example

The combined resistance R in the following series circuit is 60 Ω.

What is the resistance value of R2? A.     100 Ω               B.     30 Ω               C.     20 Ω               D.     40 Ω

Step 1: Write down the equation for the combined resistance in series

R = R1 + R2 + R3

Step 2: Substitute the values for total resistance R and the other resistors

60 Ω = 30 Ω + R2 + 10 Ω

Step 3: Rearrange for R2

R2 = 60 Ω – 30 Ω – 10 Ω = 20 Ω

### Resistors in Parallel

• When two or more resistors are connected in parallel, the combined resistance decreases
• In the below circuit, the combined resistance of the resistors R1 and R2 is less than if they were connected in series Resistors connected in parallel

• This happens because each resistor creates an extra path along which the charge can flow
• This allows more charge to flow overall
• This leads to a smaller overall resistance
• The advantages of this kind of circuit are:
• The components can be individually controlled, using their own switches
• If one component stops working the others will continue to function ### Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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