In this portion of the lab exercise, you will the cold resistance, R_0, a light

Question

In this portion of the lab exercise, you will the cold resistance, R_0, a light bulb filament using a DMM measure of shown in resistance mode, then you will connect the light bulb in a circuit as in the figure and measure the current I through the filament and the voltage V across the filament: I = _____ amps and V = _____ volts. Using Ohm's Law you can now compute the hot resistance, R_H, of the filament. Cold Resistance R_0 = _____ Hot Resistance R_H = _____ Ohm. Using the expression R_H = R_0 [1 + alpha (T_H - T_C)] you can compute the temperature of the filament, T_H. Note that alpha = 4.5 times 106-3/degree C Hot Temperature = _____ Repeat your measurements from part I using the lightbulb and a diode. Your voltage range will be different than for the resistor box. Generally, the best thing to do is start with a voltage that gives you a good "maximum" for each and then work backwards. For the diode, use 6 voltages in one direction and then reverse the polarity (switch red and black, the DMM should read negative voltages) to see what changes. Record your measurements in the tables on the next page.

Explanation / Answer

I am plugging the values in the expression provided by you which will allow you to calculate TH .

RH = V/I = 1.41/2.2= 0.641 ohms apprx

0.641= 1.4 [ 1+ 4.5 x 10^-3 (TH- Tc) ]

simpliyfing this expression further,

0.641/ 1.4 = 1+ 4.5 x 10^-3 (TH- Tc)

0.4577 = 1+ 4.5 x 10^-3 (TH- Tc)

0.4577 -1 = 4.5 x 10^-3 (TH- Tc)

-0.542 / 4.5 x 10^-3 = (TH- Tc)

-120.4906 = TH - TC

TH = Tc -120.4906

therefore, you can plug the value of TC and find TH

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