Question

The “power cube” transformer for a portable CD player has an output of 4.5 V and 500 mA (both rms) when plugged into a 120V/60Hz outlet. Part A If the primary coil has 1220 turns of wire, how many turns are on the secondary coil? I found the answer to part A: N=46 turns. Part B What is the peak current in the primary coil?

Answer #1

**Apply in a transforner**

**Ns/Np = Vs/Vp = Is/Ip**

**where NS ans Np are seconda dr and primary
tunrs**

**Vs and Vp are secondary and primary
volatges**

**Is and Ip are secondary and prianry
currents**

**also in ideal tansformer output P = input P**

**so VsIs = VpIp**

**part A: Np/Ns = Vp/Vs**

**Ns = Vs/Vp * Np**

**Ns = 4.5 * 1220/120**

**Ns = 46 turns**

**-----------------------------------------------**

**use Ip = Is * Ns/Np**

**Ip = 500 * 46/1220**

**Ip rms = 18.85 mA**

**Ip peak = 1.414 * 18.85 = 26.65 mA or 27 mA**

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