Thermal energy generated by the electrical resistance of a 5-mm-diameter and 4-m-long bare cable is dissipated to the surroundin
g air at 20°C. The voltage drop and the electric current across the cable in steady operation are measured to be 60 V and 1.5 A, respectively. Disregarding radiation, estimate the surface temperature of the cable. Evaluate air properties at a film temperature of 60°C and 1 atm pressure. Is this a good assumption?
1 answer:
Answer:
surface temperature = 128.74⁰c
Explanation:
Given data
diameter of cable = 5 mm = 0.005 m
length of cable = 4 m
T∞ ( surrounding temperature ) = 20⁰c
voltage drop across cable ( dv )= 60 V
current across cable = 1.5 A
attached to this answer is the comprehensive analysis and solution to the problem.
The assumption made is not a good one since the calculated Ts ( surface temperature ) is very much different from the assumed Ts
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Answer:
Final length= 746.175 mm
Explanation:
Given that Length of aluminium at 223 C is 750 mm.As we know that when temperature of material increases or decreases then dimensions of material also increases or decreases respectively with temperature.
Here temperature of aluminium decreases so the final length of aluminium decreases .
As we know that
Now by putting the values
ΔL=3.82 mm
So final length =750-3.82 mm
Final length= 746.175 mm
Answer:
Part 1: It would be a straight line, current will be directly proportional to the voltage.
Part 2: The current would taper off and will have negligible increase after the voltage reaches a certain value. Graph attached.
Explanation:
For the first part, voltage and current have a linear relationship as dictated by the Ohm's law.
V=I*R
where V is the voltage, I is the current, and R is the resistance. As the Voltage increase, current is bound to increase too, given that the resistance remains constant.
In the second part, resistance is not constant. As an element heats up, it consumes more current because the free sea of electrons inside are moving more rapidly, disrupting the flow of charge. So, as the voltage increase, the current does increase, but so does the resistance. Leaving less room for the current to increase. This rise in temperature is shown in the graph attached, as current tapers.
