P280 Lab Manual
Revised 3/11/2015
Physics 280
Lab Manual
Spring 2013
1
P280 Lab Manual
Revised 3/11/2015
2
Physics 280 Lab Manual Contents
Lab
Subject
Page
1
Electrostatics
3
2
Ohm’s Law
6
3A
The Voltmeter
9
3B
The Ammeter
11
3C
The Bridge Circuit
12
4
The Oscilloscope
14
5
Magnetic Fields
16
6
The Electric Motor
18
7
Electromagnets
20
8
Inductance
22
9
RC Circuits
24
10
RL Circuits
26
11
RLC Circuits
28
12
The Rectifier
30
Lab Protocol
32
P280 Lab Manual
Revised 3/11/2015
Lab 1: Electrostatics
3
Name: _________________________
1. Theory

Coulomb’s law is
Stamp
F k
Q1Q 2
r
2
k  9.00  10 9 N  m 2 / C 2
2. Charge Transfer
2.1
Set up a pith ball hanging from a string. Discharge the ball.
Rub a rubber rod with a piece of silk. Carefully touch the tip of the rod to the pith
ball. Keep other things (especially hands and clothing) well away from the area.
This process is called “charging.”
Bring the tip of the rod close to the ball without touching. What happens?
2.2
Charge the ball again. Rub the rod again and bring it close to the ball. Describe
what happens. How is it different from the previous case?
On the microscopic level, what happens when you rub the rod?
On the microscopic level, what happens when you touch the rod to the ball?
What two things do you conclude about electric charge?
Check with your instructor before continuing.
2.3
Charge the ball again. Rub a glass rod with some fur. Bring it close to the pith
ball without touching. Describe what happens. How is it different from part 2.1?
From this, what two things do you conclude about electric charge?
Check with your instructor before continuing.
3. Polarization
3.1
Set up a pith ball hanging from a string. Discharge the ball.
Rub a rubber rod with a piece of silk. Bring it close to the pith ball but without
touching. Describe what happens.
How can there be an effect if the pith ball is neutral?
P280 Lab Manual
Revised 3/11/2015
What is happening inside the pith ball?
Why is the pith ball attracted and not repelled?
3.2
Repeat the experiment with a glass rod. What does this tell us?
4. Shielding
4.1
Charge the pith ball and the rod. Can you shield the ball from the rod with a
piece of paper? With a sheet of aluminum? Explain.
4
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5. Coulomb’s Law
5.1
Draw a picture of the Coulomb’s law apparatus here:
5.2
Set your power supply to 3 kV. Find the d vs. . Graph  vs.1/d2.
d (cm)
Angle ()
5
6
8
10
12
15
20
Table 4.1 Angle vs. d
1/d2
P280 Lab Manual
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Lab 2A: Ohm’s Law
6
Name: _________________________
1. Theory

The definition of resistance is from Ohm’s Law: i  V / R
Stamp

The total voltage drop around a loop must equal the battery
or supply voltage: V1  V2  V3    VB

Currents are equal in series; voltages are equal in parallel.
2. Resistance
2.1
Connect your power supply to a light bulb. Connect your meters so you can
measure V and I at the same time. Draw a circuit diagram here:
2.2
Plot I as a function of V for several values up to the bulb’s maximum.
Table 2.1 I vs. V
V
I
How do you find R from this graph? Where is R highest? Lowest? Why?
2.3
Adjust the voltage until the current is at its practical maximum. Measure V and
calculate R. Repeat with the second bulb.
V = __________
I = __________
R1 __________ 
V = __________
I = __________
R2 __________ 
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3. Current and Voltage in series
3.1
Connect your power supply to two bulbs in series. Draw a circuit diagram:
Measure I at various points in the circuit. Label these points on your diagram.
Table 3.1 Currents in Series
Point
Current
(mA)
Explain your results.
3.2
Connect the black lead of the voltmeter to the black terminal of the power supply.
Measure V at the same points you measured I.
Table 3.2 Voltages in Series
Point
Voltage
(mA)
Explain your results.
3.3
Predict the series resistance: RSERIES = __________ 
Use V and I to measure the series resistance: RSERIES = __________ 
Find the % difference: __________
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4. Current and Voltage in parallel
4.1
Connect your power supply to two bulbs in parallel. Draw a circuit diagram:
Measure I at various points in the circuit. Label these points on your diagram.
Table 4.1 Currents in Parallel
Point
Current
(mA)
Point
Current
(mA)
Explain your results.
4.2
Measure V at the same points you measured I.
Table 4.2 Voltages in Parallel
Point
Voltage
(mA)
Point
Voltage
(mA)
Explain your results.
4.3
Predict the parallel resistance: RPARALLEL = __________ 
Measure the parallel resistance: RPARALLEL = __________ 
Find the % difference: __________
P280 Lab Manual
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Lab 3A: The Voltmeter
9
Name: _________________________
1. Theory
1.1
A voltmeter is hooked in parallel to the voltage being measured. An ideal
voltmeter has infinite resistance.
To analyze a real meter, we model it as a perfect voltmeter (R = ∞) in parallel
with an internal resistance r.
Call the power supply voltage VPS, the internal
resistance of the meter r, and the meter reading VM.
For the circuit shown, find VM in terms of VPS, R, and r:
R
Power
Supply
Write 1/VM as a function of R:
1.2
Set up the circuit shown. Set R = 50 k and VPS = 3V.
Increase R by increments of 50 k, up to 500 k. Graph 1/VM as a function of R.
Find r. Do this for all three meter ranges. You will need to increase VPS as you
change to higher ranges.
R
(k)
VM
(3 VFS)
VM
(15 FS)
VM
(30 VFS)
V
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Calculate Ohms per Volts Full Scale (VFS) for each range.
VFS
1.3
/VFS
r ()
Repeat 1.2 for a DMM. Use the 2V, 20V, and 200V ranges. Use R = 200 k to
900 k in increments of 100 k. Also, do this for an oscilloscope.
R
(k)
VM
(2 VFS)
VM
(20 VFS)
VM
(200 VFS)
Calculate Ohms per Volts Full Scale (VFS) for each range.
VFS
2
20
200
Scope
r (M)
VM
(Scope)
P280 Lab Manual
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Lab 3B: The Ammeter
1.
Ammeters
1.1
Theory
11
Name: _________________________
To analyze a real ammeter, we model it as a perfect ammeter (r = 0)
in series with an internal resistance r, as shown.
A
A
=
For circuit 1, we want to find IA in terms of VPS, R1, R2, and r. We will
assume that R1 is much bigger than R2 or r, so
𝐼𝑃𝑆 =
r
𝑉𝑃𝑆
⁄𝑅
1
R1
Since R2 and r are in parallel we can write:
𝐼2 𝑅2 = 𝐼𝐴 𝑟
Power
Supply
This lets us write 1/IA as a function of 1/R2:
1
𝑅1 𝑅1 𝑟 1
=
+
∙( )
𝐼𝐴 𝑉𝑃𝑆
𝑉0
𝑅2
1.2
R2
Circuit 1
Set up circuit 1. The correct settings for VPS and R1 vary as you change scales
and are shown in the table below.
Measure IA as R2 is lowered from 10 to 1. Graph 1/IA as a function of 1/R2.
Find r. Do this for .05 and 0.5 meter ranges.
1.3
AFS (A)
VPS (V)
R1 ()
.05
2.5
50
.5
0.5
2
r ()
Repeat for a DMM. Try three different ranges, using the VPS and R shown.
AFS (mA)
VPS (V)
R1 ()
200
0.5
5
20
5
250
2
10
5000
r ()
A
P280 Lab Manual
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Lab 3C: The Bridge Circuit
12
Name: _________________________
1.
The Galvanometer
1.1
A galvanometer is a very sensitive ammeter. It does not tell
you how much current is flowing, only in what direction.
1.2
R1
Find the potential at point A in terms of VPS, R1, and R2:
A
R2
Write the relationship between the four resistors in circuit 2 so
that points A and B are at the same potential.
Circuit 1
R1
Power
Supply
R3
A
R2
Circuit 2
B
R4
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4.3
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13
We will use circuit 3 to find an unknown resistance R4 by selecting values for the
other three resistors so that VA = VB. If this is the case, how much current flows
through the galvanometer?
If current flows to the right through the galvanometer in circuit 3, is R4 too big or
too small?
Determine your unknown R.
R1
Power
Supply
R3
G
R2
Circuit 3
R4
P280 Lab Manual
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Lab 4: The Oscilloscope
14
Name: _________________________
1. Setup
1.1
Set your oscilloscope with the help of your instructor.
Stamp
Connect a microphone or small speaker to the scope. See
what happens when you make noise. Try a tuning fork.
2. DC Power Supply
2.1
Hook your DC supply to channel 1. Set the trace to the middle of the screen.
Examine what happens when you turn (a) the V knob on the supply and (b) the
V/Div knob on the scope.
Set your trace to the top of the screen. Switch the leads from the PS and see
what happens.
3. AC Function Generator
3.1
Set your trace to the middle of the screen. Hook channel 1 to the function
generator (FG). Set the FG to 1 kHz and examine the trace.
See what happens when you change the following:
Frequency on the FG
Amplitude on the FG
S/Div on the scope
V/Div on the scope.
C = 0.5 F
4. RC Hi-pass filter
4.1
Set up the following circuit:
Display VIN and VR on your scope.
Make sure the black lead to the
scope connects to the black lead
from the FG.
Set the FG to 1 kHz.
Red
Black
R=
320 
P280 Lab Manual
4.1
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15
Find VFG and VR for different frequencies. Graph G(f) on a semilog plot.
Table 3.1 Gain of an RC Circuit
f (Hz)
VFG
VR
G
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
4.2
Measure the phase shift and graph (f) on a semilog plot.
Table 3.2 Phase Shift of a Capacitor
f (Hz)
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
t
T

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Lab 5: Field of a Bar Magnet
Name: _________________________
1. Mapping B
1.1
Lay a bar magnet on a piece of paper. Map out the B-field
with a compass.
Stamp
2. Finding the Strength of B
2.1.1 Move all magnets far away. Use your compass and
protractor to make reference lines going east-west and north-south.
Set the meter stick so it points east-west with the 10 cm mark at the intersection
of the reference lines.
Place your compass on top of the meter stick at the 10 cm mark.
Rotate the compass until the angle reads 0.
Place the magnet on top of the meter stick pointing east-west.
S
W
N
E
Move the magnet towards the compass, recording the distance and the compass
angle in the column labeled “polar.” Find B  (50)Tan( ) . The Earth’s field is 50
µT.
Polar
d (cm)
20
25
30
35
40
50
60
70
 ()
B (µT)
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Repeat the procedure, but with the meter stick pointing northsouth. The magnet should again be oriented east-west.
N
Equatorial
d (cm)
 ()
B (µT)
20
25
30
35
40
50
60
70
N
3.
Analysis
3.1
Graph B vs. d for both orientations. Do a power fit and find the exponent.
S
S
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Lab 6: The Electric Motor
Name: _________________________
1. Theory
1.1
A motor converts electricity into a spinning motion.
Stamp
2. The Homopolar Motor
2.1
Build a homopolar motor and see if you can figure out
what things are essential for a motor to work.
3. A Better Motor
3.1
Use a square object as a former to make a rotor with 3
loops of wire. The rotor should be symmetrical and wellbalanced.
3.2
Create two bearings out of paper clips.
Attach the bearings to the battery with a rubber band.
Clamp the battery into place horizontally and put a magnet on it.
Put the rotor onto the bearing.
3.3
On this diagram indicate the following with arrows:



The direction of the current in the rotor.
The direction the magnetic field from the button magnet is pointing.
The forces on the rotor and the direction it will spin.
With these diagrams, explain how the motor works through one revolution:
Battery
Battery
Battery
Magnet
Magnet
Magnet
P280 Lab Manual
3.2
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Scrape the insulation off of the top half of one end of
the rotor as shown.
19
Scrape off
insulation here.
What function does the half-removed insulation
serve?
6.2
What things are essential for any motor? List four things you could change to
increase the power or speed of your motor.
P280 Lab Manual
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Lab 7: Field of an Electromagnet
20
Name: _________________________
1.1
An electric current will create a magnetic field.
2.1
Hook up a DC power supply, a coil and a
switch.
Power
Supply
Use compasses to map out the coil’s B-field.
Switch
Coil
Draw a picture of the coil and its field.
2.2
Tape a piece of paper to the table. Use a compass and protractor to draw lines
going North-South and East-West.
Place the meter stick oriented East-West. The North-South line on the paper
should cross the meter stick at the 10 cm mark.
W
E
Place the compass at the 10 cm mark and rotate it so that 0° points north. Use a
small piece of tape to attach the compass to the meter stick.
Place the coil at the 60 cm mark at right angles to the compass needle. Have the
coil resting on small blocks so it is slightly above the meter stick.
Connect a decade resistor into the circuit and set RVAR to 1 k. Set your power
supply to 1 V.
Increase the current and measure the compass deflection. As you increase the
current the needle should increase its deflection from 0º to 90º. If it goes from 0º
to 270º flip either the orientation of the coil or swap the leads from the power
supply.
Assume the Earth’s field is BE = 50 T and use BCOIL = BE Tan() to find the
strength of the field. Graph B vs. I.
2.3
Now fix the supply voltage at 10 V. Measure B for various distances. To change
the distance, move the entire meter stick carefully along the east-west line.
Graph B vs. d and do a power fit.
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Lab 8: Inductance
22
Name: _________________________
1. Theory

Magnetic flux is defined as   NABCos( )
Stamp

A changing magnetic flux through a coil creates a voltage
according to Faraday’s Law: V   / t
2. Inductance
2.1
Hook a coil to an oscilloscope.
Use the magnet to make electricity.
Scope
What factors determine the voltage generated?
Coil
(a) _____________________________________________________________
(b) _____________________________________________________________
(c) _____________________________________________________________
Use the formulas above to estimate the B of your magnet:
B = _______________ T
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4. Mutual Inductance
4.1
Hook up the circuit shown. Include a switch in the circuit.
Power
Supply
Switch
Scope
Coil
Coil
What happens when you close the switch? When you open the switch?
________________________________________________________________
4.2
Hook up a function generator in place of the power supply. Remove the switch.
Try this for (a) different frequencies, (b) different coils, and (c) different
configurations (distance and coupling)
What factors make the signal larger or smaller?
________________________________________________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________
________________________________________________________________
What uses could this arrangement have?
(a) _____________________________________________________________
(b) _____________________________________________________________
P280 Lab Manual
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Lab 9: RC Circuits
24
Name: _________________________
C = .5 F
1. DC Response
1.1
Hook up the following circuit:
Red
Choose a square wave on your function
generator. Use this to find the time
constant of your circuit.
 = ________
R=
320 
Black
RC = ________
2. Impedance of a Capacitor
2.1
Find VFG and VR for different frequencies. Graph G(f) on a semilog plot.
Table 3.1 Gain of an RC Circuit
f (Hz)
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
VFG
VR
G
P280 Lab Manual
2.2
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25
Measure the phase shift and graph (f) on a semilog plot.
Table 3.2 Phase Shift of a Capacitor
f (Hz)
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
t
T

P280 Lab Manual
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Lab 10: RL Circuits
26
Name: _________________________
1.
DC Response
1.1
Hook up the following circuit:
L
Red
Choose a square wave on your function generator.
Use this to find the time constant of your circuit.
 = ________
R
Black
L/R = ________
2. Gain of an RL Circuit
2.1
Select an inductor. Calculate R = 2f0L, where f0 = 1 kHz. Find VFG and VR for
different frequencies. Graph G(f) and the phase shift (f) on a semilog plot.
Table 3.1 Z of an Inductor
f (Hz)
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
VFG
VR
G
Scope
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3.2
Table 3.2 Phase Shift of an Inductor
f (Hz)
100
178
320
560
1k
1.78k
3.2k
5.6k
10k
t
T

P280 Lab Manual
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Lab 11: RLC Circuits
28
Name: _________________________
1. Theory

The gain is G = VR/ VFG.
Stamp

The phase shift is  = (t/T)*360. If VR leads VFG,  is
positive.
2. Tank Circuit
2.1
Hook up this circuit. Connect your scope across R. Set C and R according to
your inductance value and the table below.
L
L (mH)
R ()
C (µF)
43
100
0.60
360
900
0.07
470
1200
0.05
30
75
0.84
C
Red
f (kHz)
VFG
VR
G
R
Black
t

0.10
0.18
0.32
0.56
1.0
1.8
3.2
5.6
10
Peak =
2.2
Graph G(f) on a semilog plot. Explain the shape of this graph. Graph (f) on a
semilog plot.
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3. Tank Circuit
3.1
Hook up this circuit. Connect your scope across R. Set C and R according to
your inductance value and the table below.
f (kHz)
VFG
L (mH)
R ()
C (µF)
43
100
0.60
360
900
0.07
470
1200
0.05
30
75
0.84
VR
G
t
0.10
0.18
0.32
0.56
1.0
1.8
3.2
5.6
10
Peak =
3.2
Graph G(f) on a semilog plot. Graph (f) on a semilog plot

P280 Lab Manual
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Lab 12: The Rectifier
30
Name: _________________________
1. Theory
1.1
Build the following circuits, Display the output of the function
generator (FG) on channel 1 and the voltage across the
resistor (VOUT) on channel 2. Draw the output.
Stamp
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Appendix 1: Lab Protocol
At the beginning of each lab I will lay out cards with each student’s name and place the
cards on the tables. You will have a different lab group each week.
It is very important to be on time. At the beginning of each lab roll will taken.
Lab reports are due the following week at the beginning of your lab session.
If you miss a lab call and see if you can attend another lab session. This will be done
only if you have a good reason, such as a serious illness, for missing lab. If the lab
cannot be made up an alternate assignment will be given. If you don’t have a good
reason the lab will be scored as a zero.
The Lab Report
A report should have the following, all stapled together:
1.
2.
3.
4.
5.
The original lab handout with my stamp on it.
Any additional sheets on which you wrote down data.
Any graphs you make in lab.
Answers to all the questions in the lab.
A TYPED conclusion.
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Grading
Each lab is graded from 0 to 100. Grading will be based on the following:









The lab is stamped. (100 points)
You were ready for the lab and participated actively in the lab. (15 points)
All the necessary data was taken. The data is clear and neat. (20 points)
All data has units. (5 points)
The number of digits is correct (not too many or too few). (5 points)
Graphs: (10 points)
o The axes are labeled and units are shown.
o The graph has a title at the top.
o The data points are NOT connected.
o An appropriate fit line is there if required.
The error analysis is reasonable. (10 points)
All questions are answered completely, clearly, and neatly. (20 points)
The report: (30 points)
o The report is not too short or too long (about one page is typical).
o The phenomenon being studied is described and a theory is given.
o The procedure is BRIEFLY described.
o The theory is compared with the actual results. This will usually include a
BRIEF discussion of uncertainties.
o A conclusion is drawn about theory. To what accuracy is it true? How
much confidence can you place in it based on your data? Is the theory true
only within certain limits or under some circumstances?
Point values are given to show how many points might be deducted for incorrect
procedure or missing items.
33