Circuits & Ohm's Law — Drills · Grade 12 Science
Chapter: Electricity, Magnetism & CircuitsWhat these drills covers
By the end of Circuits & Ohm's Law you should be able to:
- I can apply Ohm's law (V = IR) to find voltage, current, or resistance in a circuit.
- I can find the total resistance of resistors wired in series and in parallel.
- I can calculate electrical power with P = IV and relate it to energy used.
6 questions, numeric and multiple choice, each with a worked explanation.
Vocabulary used: Ohm's law, series circuit, parallel circuit, equivalent resistance, electrical power.
Problem 1
A 20 V battery is connected to a 5 Ω resistor. Find the current.
Answer and explanation
4 A
I = V ÷ R = 20 ÷ 5 = 4 A.
Problem 2
A current of 3 A flows through a 6 Ω resistor. Find the voltage across it.
Answer and explanation
18 V
V = IR = 3 × 6 = 18 V.
Problem 3
Resistors of 2 Ω, 3 Ω, and 7 Ω are connected in series. Find the total resistance.
Answer and explanation
12 Ω
In series, resistances add: 2 + 3 + 7 = 12 Ω.
Problem 4
Two 10 Ω resistors are connected in parallel. Find the equivalent resistance.
Answer and explanation
5 Ω
1/R = 1/10 + 1/10 = 2/10 = 1/5, so R = 5 Ω.
Problem 5
In a parallel circuit, if one branch is switched off, the other branches:
- keep working normally
- receive double the voltage
- reverse their current
- all stop working too
Answer and explanation
keep working normally
Each branch of a parallel circuit is independent, so switching one off leaves the others running normally at the same voltage.
Problem 6
A current of 3 A flows through a 4 Ω resistor. Find the power dissipated. (Use P = I²R.)
Answer and explanation
36 W
P = I²R = 3² × 4 = 9 × 4 = 36 W.