A trtoansformer for an answering machines takes an AC voltageof 170v (maximum, o

Question

A trtoansformer for an answering machines takes an AC voltageof 170v (maximum, or peak-to-peak) as its input and provides 7.8 V(rms) as its output to the answering machine. a) What is the turns ratio between the primary and secondary? b). When not answering the machines uses a max. power of5.0W . What is the current (rms) drawn from the 170V line? A trtoansformer for an answering machines takes an AC voltageof 170v (maximum, or peak-to-peak) as its input and provides 7.8 V(rms) as its output to the answering machine. a) What is the turns ratio between the primary and secondary? b). When not answering the machines uses a max. power of5.0W . What is the current (rms) drawn from the 170V line?

Explanation / Answer

Convert 170v peak to peak to rms voltage: V(rms) = 170 / 2 = 120 v -- Number of turns is: N(p)/N(s) = V(p)/V(s) N(p)/N(s) = 120/7.8 N(p)/N(s) = 15.4 / 1   = 15 / 1 ---> forevery 15 turns in the primary, the secondary has 1 -- Assuminng an ideal transformer, the power in secondary = powerin primary For the current in the primary, and we are given power,so: P = V(rms)*I(rms) 5.0 = 120 * I(rms) I(rms) = 5.0/120 I(rms) = 0.0416 amps = 42 mA -- -- Hope this helps.

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