3. (a) If an ac power source produces a voltage delta V = Vo sin omega t and out

Question

3. (a) If an ac power source produces a voltage delta V = Vo sin omega t and outputs a current I= I 0 sin omega t, then the load attached to the power supply has an equivalent resistance defined by Req = V0/I0. Suppose that the actual load is a transformer with NP turns in the primary coil and Ns turns in the secondary coil. The secondary coil is attached to a resistor R. Calculate the equivalent resistance of this load in terms of R and NP/NS.

(b) If the power source generates an emf E = E0 sin omega t and has internal resistance Rint, calculate the current and voltage it outputs when attached to a load Req. What is the time averaged power P dissipated by the load? For given values of E0 and Rint, what value of Req maximizes the power P? (You can determine this by setting the derivative dP/dReq = 0.

(c) Suppose your power source is an audio amplifier with Rint = 4 omega, and you wish to drive current through an electromagnetic coil with resistance R = 0.1 omega . Design a transformer to use as in part (a), by choosing NP/NS so that the power dissipation (and therefore the current) in the load coil is as large as possible.

CIRCUIT ABOVE IN IMAGE.

Explanation / Answer

(a) ep/es = Np/Ns

( e-Rint)/iR = Np/Ns

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