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Physics of a Light Bulb
Objective:
The objective of this lab was to investigate the physics of a light bulb involving
voltage, current, temperature, and to validate the StefanBoltzmann law. Under low
temperature, the light bulb obeys Ohm’s law(V=I*R). This means that voltage across the
light bulb, V is directly proportional to the current, I. Under ohmic condition, the voltage
versus current graph should form a line with a constant slope of R(resistance). However,
as the temperature increases, the light bulb will not obey Ohm’s law so that it is by nature
nonohmic at high temperature. This is due the increase of resistance R at high
temperature. On the other hand, the StefanBoltzmann law, P=A*T^4, shows that the
power output increases exponentially by a power of 4 with increasing temperature.
StefanBoltzmann’s law can be proved graphically in two ways. First, graphing the
power, P versus, temperature to the fourth, T^4, should create a straight line with a slope
that is close to A, the constant of proportionality. Second, graphing power, P, versus
temperature, T, should create a graph that shows exponential growth, and when the graph
is approximated to fit the mathematical model Y=A*X^B, the value for B should be close
to 4.
Procedure:
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This note was uploaded on 04/29/2008 for the course PHY 114 taught by Professor Tsen during the Fall '08 term at ASU.
 Fall '08
 tsen
 Current, Light

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