MCAT® ExamChemical and Physical Foundations of Biological SystemsEasy
A medical device uses a circuit consisting of a 12 V battery and two resistors connected in series: R1 = 4 Ω and R2 = 8 Ω. What is the total current flowing through the circuit?
- A1.0 A
- B2.0 A
- C0.5 A
- D1.5 A
Show answer & explanationAnswer & explanation
Correct answer: A. 1.0 A
For resistors in series, the total resistance (R_total) is the sum of individual resistances: R_total = R1 + R2 = 4 Ω + 8 Ω = 12 Ω. According to Ohm's Law (V = IR), the total current (I) is V / R_total = 12 V / 12 Ω = 1.0 A.
Why the other options are wrong
- B. Incorrect. This would be if total resistance were 6 Ω (e.g., if only R2 was considered or resistors were in parallel and sum of reciprocals was taken in error).
- C. Incorrect. This would be if total resistance were 24 Ω (e.g., if resistors were in parallel and an error in calculation occurred).
- D. Incorrect. This would be if total resistance were 8 Ω.
Ohm's Law & Series Resistors
Ohm's Law states that V=IR. For resistors connected in series, the total resistance is the sum of individual resistances.
- Ohm's Law: Voltage (V) = Current (I) × Resistance (R).
- Series Resistance: R_total = R1 + R2 + ...
- Current is the same through all components in a series circuit.
Memory trick: In Series, current is Single, Resistance Sums.