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Jared Young Experiment 3: Lab Report
Physics 152
10/20/11
1. State the equation for Ohms law. What do the variables V , I,
and Rstand for, and what are the units of each? Of the units
listed, which one
is equivalent to coulomb/second? (1 point)
2. From part B2 (unloaded circuit): Produce a graph of output
voltageVout as a function of the sliding contact position x,
measured from thebottom end of the slide wire resistor. Verify that
the data points fall on a
straight line rather than a curve (dont actually compute the
slope). Did
the current change while you varied the sliding contact position
x?
(Hint: Your current meter was switched off during this part, but
this
question can be answered using Ohms law and your graph.) (2
points)
3. From part C2 (unknown resistor): Produce a graph of voltage V
as afunction of current I. Compute the slope (ignoring
uncertainties in
voltage and current), which will give the resistance R (in ohms)
of the
unknown resistor. In the lab, you should also have deduced R
(and its
uncertainty R) from the color-coding on the side of the resistor
itself
(recall in-lab question 1). Does your value for R fall within
the
manufacturers expectations? (1.5 points)
4. From part D2 (identical series/parallel resistors): Using the
color code,write the value of R R of each identical resistor used
in this part of
the experiment (recall in-lab question 1). From this, compute
the totalresistance Rtot and its uncertainty R for the two cases:
(i) resistors in
series, and (ii) resistors in parallel. You will need to use the
following
two equations for computing total resistance: (2 points)Rseries
= R1+ R2
5. From part D2 (identical series/parallel resistors): Produce a
graph ofvoltage V as a function of cur- rent I for the two cases:
(i) resistors in
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series, and (ii) resistors in parallel. Include error bars on
each data point,
where V and I are the uncertainties in voltage and
currentmeasurements. Compute the slope and its uncertainty for each
graph.
(If you dont use graphing software, then show how you found
the
slope.) Compare your measured values of Rtot for the series and
parallelcases to those calculated in the previous question. That
is, compute the
percent difference for each case. (2.5 points)
6. An Ohmic device is one that obeys Ohms Law. According to your
data,are carbon resistors Ohmic devices? Support your answer
withreferences to your graphs and/or equations. (1 point)
7. From part E2 (light bulb): Produce a graph of voltage V as a
function ofcurrent I. Do all data points fall on a straight line?
Given your data, isthe resistance of a light bulb constant? Is a
light bulb an Ohmic device?
(1 point)
8. When a typical circuit is switched on, the net displacement
of electronsalong a wire is about 1 mm per second. If electrons
have such a low net
speed, why do lights and devices appear to work instantaneously
when
switched on? (1 point)
