Resistors in Series & Parallel Flashcards

All 6 cards in this deck

What is the formula for the total resistance of resistors in series?

e.g. a $3\,\Omega$ and a $5\,\Omega$ resistor in series

$R_{total} = R_1 + R_2$

e.g. $3 + 5 = 8\,\Omega$

Why does adding a second resistor in series increase the net resistance?

The charge has to pass through both resistors, so the oppositions to current add together.

Why does connecting a second resistor in parallel decrease the net resistance?

It gives the current an extra path, so the total current from the supply increases for the same potential difference.

What is the net resistance of two identical resistors connected in parallel?

Half the resistance of one of them.

e.g. two $10\,\Omega$ resistors in parallel give $5\,\Omega$.

True or false? Two $10\,\Omega$ resistors connected in parallel have a net resistance of $20\,\Omega$.

False. The net resistance of resistors in parallel is always less than the smallest single resistance — here $5\,\Omega$.

What are the steps to find the current and the potential difference across each resistor in a series circuit?

e.g. a $6\,\mathrm{V}$ supply with a $2\,\Omega$ and a $4\,\Omega$ resistor in series

1. Add the resistances: $2 + 4 = 6\,\Omega$
2. Current $I = V \div R = 6 \div 6 = 1\,\mathrm{A}$ (same everywhere)
3. $V = I \times R$ for each: $2\,\mathrm{V}$ and $4\,\mathrm{V}$