In her bathroom, Mindy has an overhead heater that consists of a coiled wire mad
ID: 2139226 • Letter: I
Question
In her bathroom, Mindy has an overhead heater that consists of a coiled wire made of nichrome that gets hot when turned on. The wire has a length of 2.1 m when it is uncoiled. The heating element is attached to the normal 120-V wiring and when the wire is glowing red hot it has a temperature of about 374
In her bathroom, Mindy has an overhead heater that consists of a coiled wire made of nichrome that gets hot when turned on. The wire has a length of 2.1 m when it is uncoiled. The heating element is attached to the normal 120-V wiring and when the wire is glowing red hot it has a temperature of about 374 degree C and dissipates 2215 W of power. Nichrome has a resistivity of 1.08 10-6 m at 20 degree C and a temperature coefficient of resistivity of 0.00040 degree C ?1. What is the resistance of the heater when it is turned on? What current does the wire carry? If the wire has a circular cross section, what is its diameter? Ignore the small changes in the wire's diameter and length due to changes in temperature. When the heater is first turned on, it has not yet heated up, so it is operating at 20 degree C. What is the current through the wire when it is first turned on?Explanation / Answer
C. Rcold = Rhot*(1-k?T) ? where ?T = 383 C => Rcold = 5.58
R = ?L/A = ?L/(?d^2/4) ==> d = sqrt(4?L/(?Rcold)) m = 7.196 *10^-4 m = 0.0007196