FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsMedium
A technician needs to determine the resistance of a resistive heating element in a 24-volt DC windshield anti-ice circuit. An ammeter in series with the element reads 8 amps when full system voltage is applied. What is the resistance of the element?
- A3 ohms
- B192 ohms
- C6 ohms
- D1.5 ohms
Show answer & explanationAnswer & explanation
Correct answer: A. 3 ohms
Ohm's Law states R = E / I. Dividing 24 volts by 8 amps gives 3 ohms.
Why the other options are wrong
- B. This is the product (E × I = watts), not resistance.
- C. This would result from doubling the current or halving the voltage incorrectly.
- D. Incorrect division, not the correct quotient of 24/8.
Ohm's Law
The relationship between voltage, current, and resistance in a DC circuit, expressed as E = I × R.
- E = voltage in volts
- I = current in amps
- R = resistance in ohms
- Rearranged forms: R = E/I, I = E/R
Memory trick: Picture a triangle: cover R, and E over I remains, like covering a slice of pie.