9th grade · Science · Unit 11 of 28
Circuits & Ohm's Law
Current, voltage and resistance
What your child practices
Circuit components and their jobs, current, potential difference and resistance with their symbols and SI units, calculating with V = I × R, and how current, voltage and resistance behave in series and parallel circuits.
New York State Learning Standards learning standard: HS-PS3-6 · Ohm's law: how voltage, current and resistance are related in a circuit
How we explain it
Children can open this short lesson before they practice.
- Current (I) is measured in amperes, potential difference (V) in volts, resistance (R) in ohms.
- Ohm’s law: V = I × R.
- In series, current is the same everywhere. In parallel, each branch gets the full voltage.
Example: A current of 4 A flows through a resistance of 6 Ω. What is the voltage? V = I × R. 4 × 6 = 24. Answer: 24 V
Circuits & Ohm's Law in New York
In the New York State Learning Standards, this is unit 11 of 28 in 9th grade Science, after Energy & Magnetism and before Science & Society.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
A circuit has a current of 4 A through a resistance of 10 Ω. What is the potential difference across it, in volts?
answer boxV
40 V
Hint: V = I × R = 4 × 10 = 40 V.
Question 2
Two bulbs are connected in parallel across a 6 V battery. What is the potential difference across each bulb, in volts?
answer boxV
6 V
Hint: Each branch of a parallel circuit has the same potential difference as the source.
Question 3
Two bulbs are in series. The current through the first is 2 A. What is the current through the second, in amperes?
answer boxA
2 A
Hint: In a series circuit there is only one path, so the current is the same everywhere.
Question 4
A device has 25 V across it and a current of 5 A. What is its resistance, in ohms?
answer boxΩ
5 Ω
Hint: R = V ÷ I = 25 ÷ 5 = 5 Ω.
Question 5
How is a voltmeter connected in a circuit?
- between the battery and the switch only
- in parallel across the part being measured
- in series with the part being measured
- it is not connected
in parallel across the part being measured
Hint: A voltmeter compares the potential at two points.
Question 6
A circuit's voltage stays the same and the resistance is doubled. What happens to the current?
- It doubles
- It is cut in half
- It becomes zero
- It stays the same
It is cut in half
Hint: I = V ÷ R, so doubling R halves I.