Joule heating
Same current, same wire — so why does one part get hotter?
The heat produced when a current flows through a conductor is proportional to the square of the current, the resistance of the conductor and the time the current flows. Two resistance wires in series carry the same current, so the one with the larger resistance produces more heat each second, and the same amount of kerosene warms up faster.
Kerosene temperatures
Each line's slope is proportional to its resistance; horizontal axis: physical time.
Think about it
With two resistance wires in series, why does the kerosene in the flask with the larger resistance warm up faster?
In series the current is the same; by Q = I²Rt, the larger the resistance, the more heat produced in the same time. Both flasks hold the same mass of kerosene, so the one that absorbs more heat warms up faster. Set R₂ to 2 times R₁ and the slope of its temperature curve is exactly 2 times as steep.
Model assumptionsTwo flasks of kerosene, 0.1 kg each, starting at 20°C · all heat from the wires absorbed by the kerosene · clock sped up 10×
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.