Physics
Physics
Problem
A laboratory power supply is programmed to deliver the following square-wave voltage across a fixed 20 Ω resistor: • 60 V for the first 5.0 s • 30 V for the next 10.0 s • 0 V for the final 5.0 s Assume transition times between levels are negligible and the resistance remains constant. (a) Create a quantitative table that lists, for each of the three time intervals, the current through the resistor and the instantaneous rate at which electrical energy is converted within the resistor. (b) Determine the total electrical energy converted into thermal energy during the entire 20 s program. (c) Calculate the average power delivered to the resistor over the 20 s interval. (d) Using your results, discuss whether operating the resistor under the given voltage program would raise its temperature more, less, or the same amount as operating it at a steady 40 V for 20 s. Support your claim with quantitative evidence.Intuitive explanation
The key here is recognizing that power dissipation depends on , so different voltage levels contribute unequally to total heat even if they last different times. Calculate the instantaneous power during each phase using , then multiply by duration to find energy dissipated in each interval. Adding these gives you the total thermal energy released—a direct application of how resistive heating accumulates over time.
Intuitive explanation
The key here is recognizing that power dissipation depends on , so different voltage levels contribute unequally to total heat even if they last different times. Calculate the instantaneous power during each phase using , then multiply by duration to find energy dissipated in each interval. Adding these gives you the total thermal energy released—a direct application of how resistive heating accumulates over time.