What a learner can do afterwards
- Works a multi-stage problem that both warms and melts a sample
- Reads a temperature-time graph and names the flat sections as changes of state
- Uses a heater's power and running time as the energy supplied, and comments on losses to the surroundings
1 · Read
Warming follows Q equals m c delta T. Mass times specific heat times temperature change. Water needs 4200 J for each kilogram per degree, so 0.5 kg warmed by 10 degrees takes 0.5 times 4200 times 10, which is 21000 J.
Melting or boiling follows Q equals m L, with no temperature change at all. The energy loosens molecules instead of heating them. So 0.2 kg of ice melting at 0 degrees takes 0.2 times 334000, which is 66800 J.
A 50 W heater running 120 s supplies power times time, which is 6000 J. Some heat always leaks to the room, so the sample warms less than power times time predicts. Big exam questions chain stages: warm the ice, melt it, then warm the water, in order.
Read a temperature-time graph by shape. Slopes mean warming, while flat sections mean a change of state is running. The thermometer freezes until melting or boiling finishes, then the line climbs again.
Warm with m c delta T, change state with m L, feed heaters with power times time, and read flats as changes of state.
2 · Watch
Take it off screen
Where it sits
Learn first
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.