ASVAB (Armed Services Vocational Aptitude Battery)Electronics Information (EI)Easy
A technician is troubleshooting a simple DC circuit consisting of a 12-volt battery and a single resistor. An ammeter placed in series with the resistor measures a current of 3 amperes. What is the resistance of the resistor?
- A0.25 ohms
- B9 ohms
- C4 ohms
- D36 ohms
Show answer & explanationAnswer & explanation
Correct answer: C. 4 ohms
According to Ohm's Law (V = I * R), resistance (R) can be calculated by dividing voltage (V) by current (I). Given V = 12 volts and I = 3 amperes, R = 12V / 3A = 4 ohms.
Why the other options are wrong
- A. This would be 3V / 12A, which incorrectly swaps the values.
- B. This subtracts the values (12 - 3), which is not how resistance is calculated.
- D. This multiplies the values (12 * 3), which would be the power in watts, not resistance.
Ohm's Law
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points.
- V = I * R (Voltage = Current * Resistance)
- I = V / R (Current = Voltage / Resistance)
- R = V / I (Resistance = Voltage / Current)
Memory trick: Volts are like water pressure, Amps are the flow, Ohms are the pipe's resistance.