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X p l o r e r G L X U s e r s ’ G u i d e
131
A c t i v i ty 8 : C a pa c i t o r D i s c h a r g e
Background
In the circuit pictured above, the rate at which the voltage, V, decreases is directly
proportional to the voltage. Mathematically, this can be written:
(eq. 1)
where dV/dt is the rate of voltage change, and
τ
is a constant greater than 0
known as the Capacitive Time Constant. The negative sign indicates that the
voltage decreases over time.
Equation 1 can be rewritten:
(eq. 2)
where V is the voltage at any given time, t; and V
0
is the voltage at t = 0.
In this experiment, you will create a circuit like the one in the diagram. The GLX
will measure and graph voltage over time as the capacitor discharges. From the
collected data, you will determine the capacitive time constant,
τ
, of your circuit.
Before You Begin
Start a new experiment on the GLX.
1.
Press
to go to the Home Screen.
2.
Use the arrow keys to highlight the Data Files icon and press
to open
the Data Files screen.
3.
Press
to open the Files menu and press
to select New File.
Equipment
Quantity
Xplorer GLX
1
Voltage Probe
1
Capacitor (between 0.015
and 1 F)
1
Resistor (between 100 and
1000
Ω
)
1
Battery and battery holder
(“AA,” “C,” “D,” or similar)
1
Alligator Clip Leads
4
1
Use separate electronic components or
the PASCO EM-8678 Charge/Discharge
board, which includes a capacitor, resis-
tors, and battery holder.
C
R
V
dV
dt
-------
τ
V
–
=
ln
V
V
0
------
τ
t
–
=
F4
1
pqrs
Summary of Contents for Xplorer GLX
Page 4: ......
Page 6: ......
Page 7: ...Part 1 Users Guide...
Page 8: ......
Page 18: ...12 O v e r v i e w o f t h e G L X...
Page 94: ...88 S e t t i n g s S c r e e n...
Page 98: ...92 P r i n t i n g...
Page 104: ...98 O p e r a t i n g T e m p e r a t u r e...
Page 112: ......
Page 116: ...110 C a l o r i m e t r y...
Page 132: ...126 V o l t a g e v e r s u s R e s i s t a n c e...
Page 136: ...130 I n d u c e d E l e c t r o m o t i v e F o r c e...
Page 146: ...140 B e a t F r e q u e n c y...
Page 150: ......
Page 152: ......