To answer the following questions, you will need to use equations and informatio

Question

To answer the following questions, you will need to use equations and information from the experiments in "The Specific Heat of Aluminum" and "The Latent Heat of Vaporization of Liquid Nitrogen". (Treat this like a textbook problem; use the rules of significant figures when rounding your final values.) (a) A wire wound aluminum conductor (R = 50.00 and m = 15.00 g) is initially at 20.0 °C, The conductor, thermally insulated from its environment, is connected to a 10.00 V power supply for 3.00 minutes. What will be the final temperature of the aluminum? Assume the resistance remains constant. In this temperature range, cal 0.215 cal/g-°C. (b)With its thermal insulation removed and disconnected from the power supply, the resistor from part (a) is placed in LN2. Calculate the amount of LN2 that evaporates while the resistor is cooling from room temperature to LN2 temperature. Assume room temperature is 20.0 °C. Do not use experimental values when doing this calculation. Use accepted values only (c) While the uninsulated resistor is in liquid nitrogen, i is supplied with 10.00 V for 3.00 minutes. How much additional LN2 will evaporate? Assume the resistance remains constant.

Explanation / Answer

a. given
R = 50 ohms
m = 15 g
Ti = 20 C
V = 10 V
t = 3*60 = 180 s
Tf = ?
c = 0.215 cal / gC
hence
c = 0.89956 J/ g C
hence

mc(Tf - Ti) = V^2*t/R
hence
Tf = 46.67971 C

b. Ti = 20 C
LN2 boiling point Tf = -195.8 C
latent heat of vapourisation of LN2 = L = 200,000 J/kg
hence
mass of LN2 evaporating = m
mL = 15*0.89956(20 - Tf)
m = 0.01455 kg = 14.5593 g

c. additional N2 evaporating = m'
m'L = V^2*t/R
m' = 0.0018 kg = 1.8 g

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