When resistors are connected in parallel, the total current splits up and divides equally among the branches, while the voltage remains the same across each branch. The equivalent resistance of resistors in parallel can be calculated using the formula: 1/Requiv = 1/R1 + 1/R2 + 1/R3. In this example, the resistors 16Ω, 24Ω and 48Ω are connected in parallel to a 240V supply. Using the parallel resistance formula, the equivalent resistance is calculated to be 8Ω. Then using Ohm's Law, the total current is calculated to be 30A.

1. Resistors
Connected in parallel

2. When a number of resistors are
connected as below they are connected in
PARALLEL.
R1
R2
Battery

3. In PARALLEL connections, the total
current splits up and divides itself
amongst the different branches of the
circuit.
The pressure that pushes the
electrons along (voltage) will be the same
in each branch of the circuit. So any branch of a
parallel circuit can be disconnected without
affecting the other branches.

4. These rules apply to parallel
circuits.
• Total current (I) is the sum of the current
through each of the branches.
I = I1 + I2 + I3 + etc……..

5. The same potential difference will appear
across each branch of the circuit.
V = V1 = V2 = V3 etc….

6. When working out resistors in parallel it is
easier to group the resistors together
into one large resistor (Rt).
1 1 + 1 + 1
Rt = R1 + R2 + R3

7. A 16Ω, 24Ω and a 48Ω resistor are connected in parallel
across a 240V supply.
Work out the total current.
240V
16Ω
24Ω
48Ω

8. Method 1
Find the equivalent resistance (Rt) of all the branches and
use I = V
R
1 = 1 + 1 + 1
Rt 16 24 48
1 = = 3+2+1
Rt 48
48
1
48
2
48
3
++

9. If 1 = 6
Rt 48 then
Rt = 48
1 6 so
Rt = 8 Ω

10. Using Ohm’s Law
I = V
R
I = 240
8
I = 30A

11. Method 2
I1 = V
R1
I1 = 240
16
I1 = 15A

12. I2 = V
R2
I2 = 240
24
I2 = 10A

13. I3 = V
R3
I3 = 240
48
I3 = 5A

14. So
It = I1+ I2 + I3
It = 15+10+5
It = 30A