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## Homework Statement

Make a Voltage vs. Time graph. We know the Resistance, Voltage values, and corresponding Current Values.

## Homework Equations

We have data points for the voltage, which ranges from 0-10 volts, and we have the corresponding current values.

V(t) = V(0)*e^-(t/rc)

## The Attempt at a Solution

I was looking at equations that might help me solve this problem.

I know that V(t) = V(0)*e^-(t/rc)

rc is the time constant. But isn't RC the Resistance x the Capacitance. We had three light bulbs connected in series, so there was no capacitance. And I already solved for the resistance.

I'm just confused. Help please.

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If you're confused with the setup, here is the whole unedited problem.

!!In the following: BECAUSE OF THE POTENTIAL FOR SHOCK OR DAMAGE TO THE

ELECTRONIC INSTRUMENTS, YOU MUST ASSEMBLE YOUR CIRCUIT WITH ALL

MULTIMETERS AND POWER SUPPLY TURNED OFF.

!! THE TA WILL INSPECT YOUR CIRCUIT, AND THE TA WILL THEN TURN ON THE

POWER SUPPLY AND MULTIMETERS.

B. Keeping in mind the important

caveats above, assemble your

components as indicated in the

figure. This arrangement

should allow you to measure

the current-voltage curve for

three light bulbs in series. You

should take data points starting

from about 10 Volts down to 0

Volts. Do not exceed 10 Volts

output from the power

supply. Since the voltage

readout on the power supply is very crude it is important to record the voltage as

measured by Multimeter #1 rather than using the power supply readout. Multimeter #2

is placed between the two light bulbs and will be set to measure current; you should use

the 200 mA maximum setting for current measurement. Record a total of 20 – 30 data

points, about 2 for each unit of voltage, and be sure to take at least four points in the

range 0.10 – 1.00 Volts.

Questions

1. Use Logger Pro or some other curve plotting program to plot the current-voltage

behavior for the three light bulbs. Note any nonlinearities in your plot. What is the

source of this nonlinearity? Is it really a breakdown of Ohm’s law?

2. Fit a smooth curve to your current-voltage data using the Logger Pro fitting function or

Matlab. From this data extract the slope of the current-voltage curve when voltage is

near zero. Compare this “differential” resistance with the result of your resistance

measurement from part A for the three light bulbs. Are the two values similar?

3. Include your plot of voltage versus time for the RC circuit.

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