An electric heater is used to boil small amounts of water and consists of a 5 coil that is immersed directly in the water. It operates from a 120 V socket. How much time is required for this heater to raise the temperature of 0.50 kg of water from 11°C to the normal boiling point?
Resistance Question?
I'm assuming by 5 coil you mean a 5 ohm coil.
We need to find the power, which is in units of watts.
P = IV
Using V = IR, I = 120/5 = 24 A
P = 24*120 = 2880 W = 2880 J/s
Now let's figure out how much energy is required to heat the water. Q = mC*deltaT where C = specific heat
C = 4.1813 J/gK
Q = 500*4.18*89 = 186010 J
So the time it takes = Q/P = 64.6 s
Wow! That's awfully fast. I suspect your resistance wasn't actually 5 ohms .. or your prof didn't think about the timing properly.
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