Done on the Bell
The server picks a substance, its mass, its starting temperature, how much heat it loses to the room and a timer, plus a target band for its temperature when the timer ends (always achievable), you set the heater power, and a real heating model judges the run. Landing the temperature in the band refunds your run.
About this simulation
What it shows
A puzzle on heating a substance: which substance it is, its mass, its starting temperature, how much heat it loses to the room and the length of the timer are given, along with a target band for its temperature when the timer ends. You choose the heater power, then run it.
The key idea
A bigger heater puts in more energy every second, so the substance is hotter when the timer ends, but only while it is warming up as a liquid. While it melts or boils its temperature stays flat, so the target band is always on the part of the curve where the temperature climbs.
Try this
Run it once at the starting power and see whether it ends cooler or hotter than the band, then raise or lower the Heater power slider until the temperature at the bell lands inside the band.