A transformer is to be used to provide power for a computer disk drive that need

Question

A transformer is to be used to provide power for a computer disk drive that needs 5.6 V (rms) instead of the 120 V (rms) from the wall outlet. The number of turns in the primary is 386, and it delivers 500 mA (the secondary current) at an output voltage of 5.6 V (rms).

(a) Should the transformer have more turns in the secondary compared to the primary, or fewer turns?

There should be more turns in the secondary.There should be fewer turns in the secondary.    

(b) Find the current in the primary.
mA

(c) Find the number of turns in the secondary.
turns

Explanation / Answer

There should be fewer turns in the secondary

-----------------------------------------------------

V1 * I1 = V2 * I2

I1 = V2 * I2 / V1

= 500 * 10-3 / (5.6 / 120)

= 23.33 mA

--------------------------------------------

number of turns in the secondary =  386 x (5.6/120)

= 18 turns

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