Question

Test 2

Determine the maximum power that can be generated from an 18-V emf using any combination of a 6.0-Ohms resistor and a 9.0-Ohms resistor.

Answer 1

The maximum power that transfers in the circuit

$$P_{max}=\frac{V^2}{R_{min}}.$$

The minimal resistance of circuit would be when two resistors are connected in parallel

$$R_{min}=\frac{R_1R_2}{R_1+R_2}=\frac{6\times 9}{6+9}=3.6\:\Omega.$$

Finally

$$P_{max}=\frac{18^2}{3.6}=5\:\rm W.$$