General
Physics
Lab
P209B
LAB5.
RC
circuits
NAME:
PARTNERS:
Data
Work
Sheet
In this lab, we examine the function of a capacitor in a RC circuit and determine the time
constant, τ.
Missions:
1.
Be
familiar
with
capacitors
and
a
RC
circuit.
2.
Constructing
a
RC
circuit
3.
Monitor
the
charging/
discharging
behavior
of
a
capacitor
with
time.
4.
Determine
the
half
time
(t
½)
of
the
discharging
curve
and
calculate
τ.
Equipments:
RLC
Board,
(R=100Ω,
Capacitor
100
µF)
Function
Generator
(FG)
as
a
power
source.
(4V,
20Hz,
Square
wave)
FG
Oscilloscope
Digital
multimeter,
patchcords
R=100.Ω
C=100.µF
_
Oscilloscope
Ch1
+
Part
I.
RC
circuit
and
Charging-Discharging
Curves
1. Set
up
a
RC
circuit
as
shown
in
above
diagram.
2. Set
the
values
for
the
FG
as
following;
Output
Load
Impedance:
HI
Wave
type:
Square
waves
Amplitude:
4V,
Frequency:
20Hz
(You
may
need
to
change
these
values
later.)
3. Monitor
the
voltage
across
the
capacitor
with
the
oscilloscope.
4. After
obtaining
a
clear
charging
and
discharging
pattern
on
the
oscilloscope,
push
(BTrigger)
to
analyze
the
patterns.
5. Sketch
a
single
charge
and
discharge
pattern.
1
General
Physics
Lab
P209B
LAB5.
RC
circuits
NAME:
PARTNERS:
Part
2.
Analyzing
a
Charging-Discharging
Curve:
Determine
the
half
time
(t½)
to
obtain
the
characteristic
time
constant,
τ.
1. Measure
the
maximum
voltage
(Vmax)
and
the
minimum
voltage
(Vmin)
of
the
curve
on
the
oscilloscope.
2. Calculate
the
difference
between
Vmax
and
Vmin,
(ΔV0).
3. Find
the
half
voltage
(V½
;
the
middle
between
Vmax
and
Vmin).
4. Using
the
values
above
(Vmax,
Vmin
and
V½
)
and
the
curve
on
the
oscilloscope,
determine
the
half
time
of
discharge,
t½.
5. Calculate
the
time
constant,
(τmeasured),
using
(τ
=
t½
÷
ln2)
R
C
Vmax
Vmin
ΔV0
V½
t½
τmeasured
τexpected
6. Calculate
the
expected
time
constant,
(τexpected),
using
(τ
=
RC)
7. Compare
the
expected
time
constant
with
the
measured
value.
Part
3.
Repeat
it
with
different
capacitor.
1. Change
the
capacitance
in
the
RC
circuit.
2. Calculate
the
expected
time
constant,
(τexpected),
using
(τ
=
RC)
and
the
new
capacitance
value.
3. Sketch
the
output
curve
on
the
oscilloscope
and
explain
the
curve.
4. Adjust
the
frequency
in
the
FG
to
obtain
a
clear
charging
and
discharging
pattern
on
the
oscilloscope.
(f=
__________Hz)
5. Repeat
1
through
5
in
part.2.
R
C
Vmax
Vmin
ΔV0
V½
t½
τmeasured
τexpected
6. Compare
the
τmeasured
with
the
time
constant
found
in
part
2.
Explain.
2