Question

A step-down transformer is used for recharging the batteries of portable devices. The turns ratio N2/N1 for a particular transformer used in a CD player is 3:37. When used with 120-V (rms) household service, the transformer draws an rms current of 125 mA. (a) Find the rms output voltage of the transformer. V (b) Find the power delivered to the CD player.

W

Answer 1

Given that, the turns ratio N2/N1 for a particular transformer used in a CD player is 3:37.

The input voltage of the transformer is, V1 =120 V rms

Current drawn by the transformer is, I1 = 125 mA = 0.125 A

It implies Power, P1= V1*I1 = 120*0.125 = 15 W

a) We know that, for the transformer,

  N1/N2 = V1/V2 = I2/I1 = P1/P2 ====>1

Let rms output voltage be V2 then from equation 1 we get,

V2 = V1(N2/N1)

= 120(3/37)

V2 = 9.7297 V rms

b) We know that, from te eqation 1 we get,

P2 = P1(N2/N1)

= 15(3/37)

P2 = 1.216 W