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A.P. Physics B – Understanding Capacitance
Purpose: To investigate the relationships and properties of capacitors
Materials: Multimeter with Capacitance function, aluminum foil, textbook
Part I – Capacitance versus plate separation distance
Procedure:
1) Obtain two equal sized sheets of aluminum foil and a large textbook.
2) Place one of the sheets at page 200, for example, and the other at page 260 (this is
30 pages!).
3) Place the red probe on one sheet and the black on the other and close the book.
4) Push the select button on the multimeter until you see the units “nF”
5) Use the capacitance meter to measure and record the capacitance in nanoFarads.
6) Repeat the steps above, except change the # of pages each trial by 30 pages up to
150 pages.
7) Using Graphical analysis, plot capacitance (y) first as a function of number of
pages(x) and then as a function of inverse number of pages.
Pages
Pages-1
Capacitance
What is the relationship between Capacitance and plate separation?
Write a proportionality showing this relationship.
1.
2.
3.
4.
Part II – Capacitance versus Area of the Plates
Measure and record the Capacitance for your homemade capacitor with a page
separation of about 50 pages.
Carefully fold each aluminum foil plate in half. Measure and record the
capacitance.
Repeat each step below by folding the plates in half again 3 more times.
Using Graphical analysis, Plot Capacitance (y) versus Area(x)
Capacitance
Area
A
0.5Area
0.25Area
0.125Area
0.0625Area
What is the relationship between Capacitance and Area?
Write a proportionality showing this relationship.
When proportionalities are made into formulas what must you add?
The answer above is symbolized o and is called the vacuum permeability of free
space.
Show the complete constructed formula in the box provided
Part III – The affect of wiring capacitors in parallel and series
1. Obtain the RC Pasco circuit board. Make sure the source switch is on BATTERY.
And the main switch is on discharge.
2. The voltmeter needs to be set on the 20V setting and can be placed on the springs,
which are on the same block as the capacitor springs.
3. Take a loose wire and touch the end of the capacitor springs or wire ends. This
will reduce the charge on the capacitor to zero.
4. Place a second capacitor in the set of springs right after the mounted capacitor and
repeat the discharging technique.
5. Move the switch to charge. Measure and record the time it takes for the
capacitor(s) to charge from 0.0 V to approximately 0.70 V.
6. After the voltage has surpassed the 0.70 V mark, move the switch to discharge.
7. Measure and record the time it takes for the capacitor(s) to drain from 0.70 volts
to approximately 0.0 volts.
8. Repeat steps1-4, except place the capacitors parallel with each other. In other
words make sure that the second capacitor is attached to the SAME terminals as
the mounted capacitor.
Type of Circuit
Time (charging)
Time (discharging)
Series
Parallel
1. What effect does the total capacitance have if the capacitors are wired in series?
Explain and show.
2. What effect does the total capacitance have if the capacitors are wired in
parallel? Explain and show.