3.8 Parallel Circuits

Question 1

In parallel circuits, is the p.d. the same across all branches or different?

Answer 1

The same

Question 2

In parallel circuits, why is the work done per unit charge in a branch the same for all branches?

Answer 2

This is because each charge can only pass down one branch of the circuit, so it must transfer all the energy supplied to it by the source p.d. to whatever’s on that branch.

Question 3

In parallel circuits, the _____ current flowing round the circuit equals the _____ of all the currents flowing through the separate branches

Answer 3

total, total

Question 4

As you add more resistors in parallel circuits, does the resistance become greater or lower?

Answer 4

Lower

Question 5

Why does the resistance of parallel circuits become lower as you add more resistors?

Answer 5

• As more resistors are added, the charge flowing round the circuit has more than one branch to take. This means more charge flows round the circuit in a certain time - i.e. there’s a higher total current.
• The p.d. of the circuit is the same everywhere.
• The equation R = V / I shows that increasing the current through the circuit and keeping the p.d. fixed means that the net resistance of the circuit must decrease.

Question 6

In parallel circuits, if the resistance of one component changes, what happens to the current?

Answer 6

The current through only that branch will change, but the current through the other branches and the p.d. across them will remain the same.