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Unformatted text preview: urrent is ½, ¼, ⅛ … of its initial value). EXPLORATION
WARNING: A charged capacitor can discharge quickly producing a painful spark. Do
not handle the capacitors by their electrical terminals or connected wires by their metal
ends. Always discharge a capacitor before you use it and when you are finished
Before you build the circuit, examine each element of it. How do you know if the
battery is "good"? Is the capacitor charged? Carefully connect the two terminals of the
capacitor to ensure it is uncharged. How can you determine the resistance of the
resistor? Is there a way to confirm it?
If you have completed Charging a Capacitor (PartA), review your exploration notes
from your lab journal.
Build circuit VIII. To measure the current in the circuit, connect a DMM in series.
If you have not done so, read how to use the DMM in the Equipment appendix. Pay
special attention to the connections and settings that are used to measure voltages and
currents, and why the DMM should be connected in the circuit differently for voltage
and current measurements. Do you know why we should connect them in these ways?
Note: Make sure the + terminal of the battery is connected to the + terminal of the
capacitor! These capacitors are only designed to charge one way. If you connect the
capacitors up the wrong way, the capacitance will change in an unpredictable manner. 103 CHARGING A CAPACITOR (PART B) – 1302Lab4Prob6 Check that the polarity of the capacitor’s connection is correct and begin your
experiment. Close the circuit and observe how long it takes for the current in the circuit
to halve. How does changing the capacitance of the capacitor or the resistance of the
resistor affect this time? Choose a combination of a resistor and a capacitor that allows
you to measure this time as accurately as possible. Observe how long it takes for the
current in the circuit to successively halve in value. Is this as you had predicted?
Complete your measurement plan. MEASUREMENT
Measure the time taken for the current in the circuit to successively halve in value.
Make at least two measurements for each setup for averaging. ANALYSIS
Using the measured value of the capacitance of the capacitor, the resistance of the
resistor and the voltage of the battery, calculate the times for successive halving of the
current in the circuit. These times are what theory predicts for your circuit. Compare
them to the measured times, at which the current decreases to ½, ¼, ⅛ … of its initial
How well did your prediction agree with your results? Explain any differences.
Using these times for successive halving of the current, can you determine how long it
would take for the current to fall to zero? Does this agree with your experimental
evidence? 104 PROBLEM #7: CHARGING A CAPACITOR (PART C)
You have read on the internet that you can use a large capacitor to increase the bass
volume in your car stereo. However, you know from physics that a charged capacitor
will only provide current for a short time before it needs to be recharged. You decide to
figure out how long it will take the capacitor to recharge as a function of the total
resistance of the recharging circuit. You know that one way to quantify this time is to
measure how long it takes for the charging current to fall to one half of its initial value.
You decide to model this situation using a circuit consisting of a battery, a capacitor
(initially uncharged), and a resistor, all in series.
Instructions: Before lab, read the laboratory in its entirety as well as the required reading in the
textbook. In your lab notebook, respond to the warm up questions and derive a specific prediction
for the outcome of the lab. During lab, compare your warm up responses and prediction in your
group. Then, work through the exploration, measurement, analysis, and conclusion sections in
sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to
perform data analysis, rather than doing it by hand.
Read: Tipler & Mosca, Section 25-6. EQUIPMENT
Build the circuit shown
capacitors, and batteries.
Use the accompanying
legend to help you build
the circuits. You will also
have a stopwatch and a
digital multimeter (DMM).
Read the section The Digital Multimeter (DMM) in the Equipment appendix.
Read the appendices Significant Figures, Review of Graphs and Accuracy, Precision
and Uncertainty to help you take data effectively.
If equipment is missing or broken, submit a problem report by sending an email to
[email protected] Include the room number and brief description of the
problem. 105 CHARGING A CAPACITOR (PART C) – 1302Lab4Prob7 WARM UP
1. If you have done Charging a Capacitor (PartA), you will already have the equation
that describes the way in which the current in the circuit changes with time and
depends upon the capacitance of the capacitor and the resistance of the resistor. You
should skip to Warm-up qu...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
- Spring '14