When does a source of current deliver maximum power?

Name some sources of direct current.

The diode used in the circuit shown in the adjacent figure has a constant voltage drop of 0.5V at all currents and a maximum power rating of 100mW.What should be the value of resistor R connected in series with the diode for obtaining maximum current?

Why does a motor take more current when we start it?

In electric cell the source of current is -

A series LCR circuit with L=0.12H, C = 480 nF, R= 23 Omega is connected to a 230 V variable frequency supply. What is the source frequency for which average power absorbed by the circuit is maximum. Obtain the value of this maximum power.