CSLB C-10 Electrical ContractorElectrical Theory and CalculationsEasy
A transformer has a primary winding with 200 turns and a secondary winding with 50 turns. If the primary voltage is 480V, what is the secondary voltage?
- A60V
- B960V
- C240V
- D120V
Show answer & explanationAnswer & explanation
Correct answer: D. 120V
The voltage ratio of a transformer is directly proportional to its turns ratio. Vp/Vs = Np/Ns. By rearranging and substituting the values, Vs can be found.
Why the other options are wrong
- A. This is a calculation error, possibly inverting the turns ratio.
- B. This is an error, indicating a step-up rather than step-down transformer.
- C. This is a calculation error, possibly assuming a 2:1 ratio.
Transformer Voltage Ratio
The ratio of the primary voltage to the secondary voltage in a transformer is equal to the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.
- Formula: Vp/Vs = Np/Ns.
- Ideal transformers assume no losses.
- Used for stepping up or stepping down voltage.
Memory trick: Volts and Turns go together, but Current is backwards!