Physics 0212
DC Circuits 2
Informal Lab Report
Name:
Lab Partner:
TA:
Section 8.2 – The Time Constant of a RC Circuit
R = 5,000 Ω
C = 2,200 µF
What is the value of the RC time constant τ ?____________
Does your plot of the voltage for the charging and discharging capacitor have the shape you expected? (Does it
have the shape predicted by the equations?)
R = 50,000 Ω C = 2,200 µF
What is the value of the RC time constant τ ? ____________
Record the slope ____________ and intercept ____________ from the ln(V) versus Time plot.
What is the physical meaning of the slope and intercept?
What is the RC time constant as determined from your slope? ____________
How does this compare to the expected value of the RC time constant from above?
Assuming the value of the RC time constant determined from your slope is correct, use the value of the
resistance to calculate the capacitance _____________. How does this compare to the value listed on the
capacitor?
1
.
.
.
Charging Capacitor
i
ti
(1 − e
Vi
−ti RC
)
(
=
V0 Vi 1 − e −ti
RC
)
1
2
3
4
Mean V0
R = 50,000 Ω C = 1,000 µF
What is the value of the RC time constant τ ? ____________
Record the slope ____________ and intercept ____________ from the ln(V) versus Time plot.
What is the physical meaning of the slope and intercept?
What is the RC time constant as determined from your slope? ____________
How does this compare to the expected value of the RC time constant from above?
Assuming the value of the RC time constant determined from your slope is correct, use the value of the
resistance to calculate the capacitance _____________. How does this compare to the value listed on the
capacitor?
Charging Capacitor
i
ti
Vi
(1 − e
−ti RC
1
2
3
4
Mean V0
2
)
(
=
V0 Vi 1 − e −ti
RC
)
Section 8.3 – Solar Cell Measurements
Record the length (L) ____________ and width (W) ____________ of the solar cell.
Calculate the area ( A = LW ) of the solar cell ____________.
Record the internal resistance of the galvanometer ( Rm ) ____________.
Record the height (h) ____________ of the center of the filament above the solar cell.
RD
Current
(I)
x=
1
I
δx
Resistance
(=
R RD + Rm )
δR
Power
( P = I 2R )
5.0 mA
4.5 mA
4.0 mA
3.5 mA
3.0 mA
2.5 mA
2.0 mA
1.5 mA
1.0 mA
0.5 mA
Record the slope ____________ and intercept ____________ from the R versus x plot.
What is the physical meaning of the slope and intercept? (Look at Equation 8.8.)
Explain how you could show the maximum power occurs at R = Rc in Equation 8.10.
3
δP
Find the maximum power ( Pmax ) in the Power versus Rc plot ____________.
Record the resistance that corresponds to this maximum power ____________.
Calculate the maximum efficiency using Equation 8.11 ____________.
Section 8.4 The Electrocardiograph (ECG)
Record the voltage at the R wave peak ____________ and the voltage at the S wave minimum ____________.
Use Ohm’s law to find the current (I) in the body at the voltage of the R wave peak ____________. Would it be
possible to measure this current with a 1 mA Galvanometer?
Record the period of one heartbeat ( T = ∆t ) ____________.
Calculate the frequency of your heart in beats per minute ( f = 1 T ) ____________.
Muscle movements can generate electrical currents that overwhelm a voltmeter trying to measure the action
potential from your heart. To see this, move your arms around as you take data. Can you still see the QRS
complex? How does the maximum voltage compare to the R peak you saw previously? Describe what happens
if you stop moving your arms halfway through the data collection.
Describe what happens if you remove the black (reference) wire and then take data. Is it still possible to see the
QRS complex? Is there more noise (jitter) in the EKG?
4
Describe what happens if you remove the green wire in Figure 8.6 (with the black connected as shown).
Describe what happens if you switch the green and black wires in Figure 8.6.
Describe what happens if you connect the green and black wires to the same electrode.
Describe what happens to the P, Q, R, S and T waves if you switch the red and green wires in Figure 8.6.
5