An engineer designed a transformer to convert 120 V (rms) to 6.0 V (rms). The number of turns in the primary is 540, and the secondary current is 610 mA at an output voltage of 6.0 V (rms).
-What is the current in the primary?
A)30.5 mA
B)4.50 mA
C)32.8 mA
D)136 mA

Question

An engineer designed a transformer to convert 120 V (rms) to 6.0 V (rms). The number of turns in the primary is 540, and the secondary current is 610 mA at an output voltage of 6.0 V (rms). 
-​What is the current in the primary?
A)​30.5 mA
B)​4.50 mA
C)​32.8 mA
D)​136 mA

Quizplus · Accepted Answer

The transformer's operation is based on the principle of mutual induction, where the voltage ratio between the primary and secondary sides is equal to the turns ratio. Also, the power input equals the power output (ignoring losses). Given the primary voltage (Vp) = 120 V, secondary voltage (Vs) = 6.0 V, number of turns in the primary (Np) = 540, and secondary current (Is) = 610 mA = 0.610 A, we can find the primary current (Ip) using the power equality: VpIp = VsIs. Rearranging for Ip gives Ip = (VsIs) / Vp. Substituting the given values: Ip = (6.0 V * 0.610 A) / 120 V = 3.66 / 120 = 0.0305 A = 30.5 mA.

An Engineer Designed a Transformer to Convert 120 V (Rms)