A laboratory hot plate is designed so that its resistive heating coil can deliver 480W of thermal power when operated at its rated potential difference. Measurements show that the coil’s resistance is 75Ω at its operating temperature.
(a) Determine the potential difference that must be applied across the coil for it to deliver its rated power.
(b) In a different laboratory only a 240V supply is available. To operate the same coil safely at its rated power, a resistor is connected in series with the coil. Calculate the value of the series resistance required.
(c) For the configuration in part (b), calculate the total power drawn from the 240V supply.
(d) Explain qualitatively how adding the series resistor changes the efficiency of converting electrical energy into heat on the hot plate, referring to the distribution of power among circuit elements.