A variable resistor R is connected across an ideal 200V d.c. supply that is rated for a maximum output power of 100W. Owing to self-heating, the resistance of R can change by up to ±20% from its cold value.
a. (i) Calculate the cold (initial) resistance that will make the supply deliver exactly its rated maximum power of 100W.
b. (ii) Determine the minimum and maximum power that the supply may have to deliver when the resistance varies within the stated ±20% range.
c. (iii) Using your results, decide whether the supply’s power rating could be exceeded at any point during operation, and justify your answer.