What is the resistance of a 6.4 m length of nichrome wire that has a radius of 0
ID: 1326960 • Letter: W
Question
What is the resistance of a 6.4 m length of nichrome wire that has a radius of 0.321 mm? How much current does it carry when connected to a 120 V source?
R =
I=
The heating element of a coffeemaker operates at 120 V and carries a current of 6.50 A. Assuming the water absorbs all of the energy converted by the resistor, calculate how long it takes to heat 0.620 kg of water from room temperature (23.0°C) to the boiling point.
Can someone help me with these problems? i have an exam tomorrow and cant figure them out. please explain into detail
Explanation / Answer
R= rnichrome*(L/A) = (10^-6ohm.m )*[6.4/((3.14*(0.321*10^-3)^2)]= 19.8 W
I=V/R = 120V/19.8 W = 6.06 A
By Joule’s law
H=I2Rt
Where H= Heat=Q
Q for mass of water m= 0.620kg required to raise temperature from 23oC to 100oC= mcT …c= specific heat
Thus,
mcT= I2Rt
t= (mcT)/(I2R)= (mcT)/(IV) = (0.620*4.187*10^3*77)/(6.5*120))= 256.3 s = 4.3 min
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