CSLB C-10 Electrical ContractorElectrical Theory and CalculationsEasy
An electrician is troubleshooting a control circuit that has a 24V supply. If a relay coil in the circuit draws 50 mA of current, what is the resistance of the relay coil?
- A480 ohms
- B4.8 ohms
- C48 ohms
- D4800 ohms
Show answer & explanationAnswer & explanation
Correct answer: A. 480 ohms
Using Ohm's Law (R = V/I), first convert the current from milliamperes to amperes, then divide the voltage by the current to find the resistance.
Why the other options are wrong
- B. This is a calculation error, possibly not converting mA to A correctly.
- C. This is a calculation error, likely off by a factor of 10.
- D. This is a calculation error, likely off by a factor of 10.
Ohm's Law (Resistance Calculation)
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Resistance (R) is calculated by dividing voltage (V) by current (I).
- Formula: R = V / I.
- Units: Resistance in Ohms (Ω), Voltage in Volts (V), Current in Amperes (A).
- Always ensure current is in Amperes before calculation.
Memory trick: V over I times R, V over I times R, V over I times R. That's Ohm's Law for me!