Problem 2
A DC source of emf E and internal resistance r supplies a purely resistive load R in series; take E and r as constant and the leads ideal. The circuit reaches steady current, the terminal voltage is U, and useful power is delivered to the load. (a) Express current and load voltage in terms of R. (b) Find the load R for maximum power and that maximum. (c) Find efficiency there, defined as load power divided by the power supplied by the ideal emf. Use SI units throughout and treat components as ideal exactly as specified. State sign conventions when writing equations and retain units in final results.
problems.proof.stepOf
problems.proof.analysis
Insert the intermediate result into the relevant definition or equation to obtain the final expression. Checking signs and limits catches a wrong branch or omitted constraint.