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A transformer inside the power supply fo...

A transformer inside the power supply for a portable CD player has 500 turns in the primary coil. It supplies an emf of amplitude 6.8 V when plugged into the usual sinusoidal household emf of amplitude 170 V. (a) How many turns does the secondary coil have? (b) If the current drawn by the CD player has amplitude 1.5 A, what is the amplitude of the current in the primary?

Text Solution

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a) The turns ratio is equal to the emf ratio
`E_2/E_1 = N_2/ N_1`
` rArr N_2 = N_ 1 E_2/E_1 = (6.8)/(170) xx 500 = 20` turns
(b) The current is inversly proportional to the emf
` I_1/I_2 = E_2/E_1 = N_2/N_1`
` rArr I_1 = E_2/E_1 I_2 = (6.8)/(170) xx 1.5 = 0.060 A`
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