Posted by physics..... on .
1500W thingy heats1.5kg water from 18C to 59C in 3.0minutes. How mcuh n-ergy was used by the thingy?
There are two ways to do this and they should agree, if all of the electrical power goes into heating the water. Let's see if they do.
Power consumed by the "thingy" is 1500 J/s * 3.0 min * 60 s/min = 270,000 J
Q = Change of water's internal energy
= m C *delta T
= 1500 g* (1.0 cal g/C)*41 C *4.18 J/cal= 257,070 J
The latter number is more reliable. The 1500 W rating of the heater may have not been quite been reached due to low voltage, or heat transferred to other regions