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 6.0 V (rms) instead of the 120 V (rms) from the wall outlet. The number of turns in the primary is 405, and it delivers 500 mA (the secondary current) at an output voltage of 6.0 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

output voltage V '= 6 V
input voltage V = 120 V
The number of turns in the primary N = 405
secondary current i ' = 500 mA
a) number of turns in the secondary compared with the primary N ' = ?
we know N ' / N = V ' / V
= 1 / 20
i.e.,secondary truns are fewer
(b) the current in the primary i = ?
i ' / i = N / N '
i = 500mA *(20 )
= 10000 mA
(c) the number of turns in the secondary N ' = N / 20 = 405/20=20.25 = 21(aprox)

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