Everything Science Grade 10

17.5 CHAPTER 17. ELECTRIC CIRCUITS

Example 13: Parallel resistors III

QUESTION

We add a third parallel resistor to the first parallel worked example configuration

(setup). The additional resistor has a resistance of3 Ω.

15 Ω 3 Ω 7 Ω

What is the total resistance in the circuit?

SOLUTION

Step 1:Analyse the question

We are told that the resistors in the circuit are in parallel circuit and that

we need to calculate the total resistance. The value of the additional

resistor has been given in the correct units,Ω.

Step 2:Apply the relevant principles

We can swap the resistors around without changing the circuit:

15 Ω 7 Ω 3 Ω

We have already calculated the total resistance of the two resistors in

the dashed box to be 4 ,77 Ω. We can replace these two resistors with a

single resistor of 4 ,77 Ωto get:

4 ,77 Ω 3 Ω

308 Physics: Electricity and Magnetism