PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
PHS 104A Ohm’s Law Practice
Problems
2026–2027 | 110 Questions & Worked Solutions
Formula & Lab Reference
Ohm’s law: V = IR; I = V/R; R = V/I. Voltage V in volts, current I in amperes, resistance R in ohms.
Power: P = VI = I²R = V²/R, measured in watts.
Energy: E = Pt; joules when t is in seconds; 1 kWh = 3.6 × 10⁶ J.
Series: R_eq = ΣR; current is common; voltage drops add.
Parallel: 1/R_eq = Σ(1/R); voltage is common; branch currents add.
Kirchhoff: At a junction, current entering equals current leaving; around a closed loop, algebraic voltage
changes sum to zero.
Meters: Ideal ammeters connect in series; ideal voltmeters connect in parallel.
Lab practice: De-energize before rewiring, verify meter range and lead ports, record uncertainty and
units, and never place an ammeter directly across a voltage source.
Independent physics laboratory practice • Page 1
,PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
Ohm’s Law: Current
Question 1. A resistor of 5 Ω has 1 V across it. What current flows?
A. 200 A
B. 0.2 A
C. 5 A
D. 5 A
Correct Answer: B. 0.2 A
Worked Solution: I = V/R = 1 V / 5 Ω = 0.2 A.
Why the Other Options Are Incorrect: A — Confuses milliamperes with amperes. C — Multiplies
voltage by resistance rather than dividing. D — Inverts the voltage-to-resistance ratio.
Question 2. A resistor of 10 Ω has 3 V across it. What current flows?
A. 3.333 A
B. 300 A
C. 0.3 A
D. 30 A
Correct Answer: C. 0.3 A
Worked Solution: I = V/R = 3 V / 10 Ω = 0.3 A.
Why the Other Options Are Incorrect: A — Inverts the voltage-to-resistance ratio. B — Confuses
milliamperes with amperes. D — Multiplies voltage by resistance rather than dividing.
Question 3. A resistor of 15 Ω has 6 V across it. What current flows?
Independent physics laboratory practice • Page 2
,PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
A. 90 A
B. 2.5 A
C. 400 A
D. 0.4 A
Correct Answer: D. 0.4 A
Worked Solution: I = V/R = 6 V / 15 Ω = 0.4 A.
Why the Other Options Are Incorrect: A — Multiplies voltage by resistance rather than dividing. B —
Inverts the voltage-to-resistance ratio. C — Confuses milliamperes with amperes.
Question 4. A resistor of 20 Ω has 10 V across it. What current flows?
A. 0.5 A
B. 200 A
C. 2 A
D. 500 A
Correct Answer: A. 0.5 A
Worked Solution: I = V/R = 10 V / 20 Ω = 0.5 A.
Why the Other Options Are Incorrect: B — Multiplies voltage by resistance rather than dividing. C —
Inverts the voltage-to-resistance ratio. D — Confuses milliamperes with amperes.
Question 5. A resistor of 25 Ω has 15 V across it. What current flows?
A. 600 A
B. 0.6 A
C. 375 A
D. 1.667 A
Correct Answer: B. 0.6 A
Worked Solution: I = V/R = 15 V / 25 Ω = 0.6 A.
Why the Other Options Are Incorrect: A — Confuses milliamperes with amperes. C — Multiplies
voltage by resistance rather than dividing. D — Inverts the voltage-to-resistance ratio.
Question 6. A resistor of 30 Ω has 6 V across it. What current flows?
Independent physics laboratory practice • Page 3
, PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
A. 5 A
B. 200 A
C. 0.2 A
D. 180 A
Correct Answer: C. 0.2 A
Worked Solution: I = V/R = 6 V / 30 Ω = 0.2 A.
Why the Other Options Are Incorrect: A — Inverts the voltage-to-resistance ratio. B — Confuses
milliamperes with amperes. D — Multiplies voltage by resistance rather than dividing.
Question 7. A resistor of 35 Ω has 10.5 V across it. What current flows?
A. 367.5 A
B. 3.333 A
C. 300 A
D. 0.3 A
Correct Answer: D. 0.3 A
Worked Solution: I = V/R = 10.5 V / 35 Ω = 0.3 A.
Why the Other Options Are Incorrect: A — Multiplies voltage by resistance rather than dividing. B —
Inverts the voltage-to-resistance ratio. C — Confuses milliamperes with amperes.
Question 8. A resistor of 40 Ω has 16 V across it. What current flows?
A. 0.4 A
B. 640 A
C. 2.5 A
D. 400 A
Correct Answer: A. 0.4 A
Worked Solution: I = V/R = 16 V / 40 Ω = 0.4 A.
Why the Other Options Are Incorrect: B — Multiplies voltage by resistance rather than dividing. C —
Inverts the voltage-to-resistance ratio. D — Confuses milliamperes with amperes.
Question 9. A resistor of 45 Ω has 22.5 V across it. What current flows?
Independent physics laboratory practice • Page 4
PHS 104A Ohm’s Law Practice
Problems
2026–2027 | 110 Questions & Worked Solutions
Formula & Lab Reference
Ohm’s law: V = IR; I = V/R; R = V/I. Voltage V in volts, current I in amperes, resistance R in ohms.
Power: P = VI = I²R = V²/R, measured in watts.
Energy: E = Pt; joules when t is in seconds; 1 kWh = 3.6 × 10⁶ J.
Series: R_eq = ΣR; current is common; voltage drops add.
Parallel: 1/R_eq = Σ(1/R); voltage is common; branch currents add.
Kirchhoff: At a junction, current entering equals current leaving; around a closed loop, algebraic voltage
changes sum to zero.
Meters: Ideal ammeters connect in series; ideal voltmeters connect in parallel.
Lab practice: De-energize before rewiring, verify meter range and lead ports, record uncertainty and
units, and never place an ammeter directly across a voltage source.
Independent physics laboratory practice • Page 1
,PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
Ohm’s Law: Current
Question 1. A resistor of 5 Ω has 1 V across it. What current flows?
A. 200 A
B. 0.2 A
C. 5 A
D. 5 A
Correct Answer: B. 0.2 A
Worked Solution: I = V/R = 1 V / 5 Ω = 0.2 A.
Why the Other Options Are Incorrect: A — Confuses milliamperes with amperes. C — Multiplies
voltage by resistance rather than dividing. D — Inverts the voltage-to-resistance ratio.
Question 2. A resistor of 10 Ω has 3 V across it. What current flows?
A. 3.333 A
B. 300 A
C. 0.3 A
D. 30 A
Correct Answer: C. 0.3 A
Worked Solution: I = V/R = 3 V / 10 Ω = 0.3 A.
Why the Other Options Are Incorrect: A — Inverts the voltage-to-resistance ratio. B — Confuses
milliamperes with amperes. D — Multiplies voltage by resistance rather than dividing.
Question 3. A resistor of 15 Ω has 6 V across it. What current flows?
Independent physics laboratory practice • Page 2
,PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
A. 90 A
B. 2.5 A
C. 400 A
D. 0.4 A
Correct Answer: D. 0.4 A
Worked Solution: I = V/R = 6 V / 15 Ω = 0.4 A.
Why the Other Options Are Incorrect: A — Multiplies voltage by resistance rather than dividing. B —
Inverts the voltage-to-resistance ratio. C — Confuses milliamperes with amperes.
Question 4. A resistor of 20 Ω has 10 V across it. What current flows?
A. 0.5 A
B. 200 A
C. 2 A
D. 500 A
Correct Answer: A. 0.5 A
Worked Solution: I = V/R = 10 V / 20 Ω = 0.5 A.
Why the Other Options Are Incorrect: B — Multiplies voltage by resistance rather than dividing. C —
Inverts the voltage-to-resistance ratio. D — Confuses milliamperes with amperes.
Question 5. A resistor of 25 Ω has 15 V across it. What current flows?
A. 600 A
B. 0.6 A
C. 375 A
D. 1.667 A
Correct Answer: B. 0.6 A
Worked Solution: I = V/R = 15 V / 25 Ω = 0.6 A.
Why the Other Options Are Incorrect: A — Confuses milliamperes with amperes. C — Multiplies
voltage by resistance rather than dividing. D — Inverts the voltage-to-resistance ratio.
Question 6. A resistor of 30 Ω has 6 V across it. What current flows?
Independent physics laboratory practice • Page 3
, PHS 104A | OHM’S LAW PRACTICE & WORKED SOLUTIONS | 2026–2027
A. 5 A
B. 200 A
C. 0.2 A
D. 180 A
Correct Answer: C. 0.2 A
Worked Solution: I = V/R = 6 V / 30 Ω = 0.2 A.
Why the Other Options Are Incorrect: A — Inverts the voltage-to-resistance ratio. B — Confuses
milliamperes with amperes. D — Multiplies voltage by resistance rather than dividing.
Question 7. A resistor of 35 Ω has 10.5 V across it. What current flows?
A. 367.5 A
B. 3.333 A
C. 300 A
D. 0.3 A
Correct Answer: D. 0.3 A
Worked Solution: I = V/R = 10.5 V / 35 Ω = 0.3 A.
Why the Other Options Are Incorrect: A — Multiplies voltage by resistance rather than dividing. B —
Inverts the voltage-to-resistance ratio. C — Confuses milliamperes with amperes.
Question 8. A resistor of 40 Ω has 16 V across it. What current flows?
A. 0.4 A
B. 640 A
C. 2.5 A
D. 400 A
Correct Answer: A. 0.4 A
Worked Solution: I = V/R = 16 V / 40 Ω = 0.4 A.
Why the Other Options Are Incorrect: B — Multiplies voltage by resistance rather than dividing. C —
Inverts the voltage-to-resistance ratio. D — Confuses milliamperes with amperes.
Question 9. A resistor of 45 Ω has 22.5 V across it. What current flows?
Independent physics laboratory practice • Page 4
