An electrical lamp filament dissipates 20 W when the current through it is 0.10 A. What is (a) the potential difference across the lamp and (b) its resistance at that current? Within what range will...

An electrical lamp filament dissipates 20 W when the current through it is 0.10 A. What is (a) the potential difference across the lamp and (b) its resistance at that current?

Within what range will the resistances lie for resistors specified as being (a) 20 R, 5 % tolerance, (b) 68 Q, 10 % tolerance, (c) 47 Q, 20 % tolerance?