Problem 2

An ideal emf source

\mathcal E

in series with internal resistance

r

supplies a resistive load

R

; all components and wires remain at fixed temperature and the circuit is in steady state. (a) Find the current, source terminal voltage, and load power. (b) Find the value of

R

for maximum load power and that maximum. (c) At the maximum-power condition, compare power delivered by the source with power dissipated internally and state the load-power efficiency.

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V_{\rm term}=IR=\mathcal E-Ir=\frac{\mathcal E R}{R+r}

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The terminal voltage is the load drop and also the emf minus the internal drop. These equivalent forms check the circuit signs.