Physics 130 Practical Test – 1:30
March 28, 2007
Name
Student #
Make a clear record of the results of your measurements. Show uncertainties of values as
specified. Write your answer in the spaces below the questions. (60 pts Total)
Optics
1. Determine the line spacing of the unknown diffraction grating with error. Record the
number written on your grating in the space below. The wavelength of the He-Ne laser is
632.8 nm. Make a record of the experiment as you would in your lab notebook using the
rest of this page and its back (if needed). (You don’t need to write a full report with
conclusion, just a full description of how you made this measurement and how you
determined the uncertainty.) (15 pts)
dsin   m m  0,1,2...
Diffraction Grating Number ___________

page 1
page 2
DC Circuits
Show uncertainties of all measured and calculated values in this section.
2.(a) Connect resistors Rblue and Ryellow in series. Connect the DC power supply across the
resistor pair. Draw a schematic circuit diagram showing the circuit and how to use the digital
multimeter (DMM) to measure the voltage across Rblue. (Resistors are covered with coloured
plastic and referred to by colour.) (3 pts)
(b) Adjust the power supply to approximately 1.00 V and use the DMM to separately measure
the voltage across Rblue and then the voltage across Ryellow . Record your results with errors
below. (3 pts)
(c) Use the measurements from (b) to calculate the total voltage with error across the
combination of Rblue and Ryellow. (Show all of your work.) (2 pts)
page 3
(d) Draw a schematic circuit diagram showing the circuit of part (a) and how you connect the
DMM to measure the current through Rblue. (3 pts)
(e) Using the DMM, measure the current passing through Rblue and record the value plus error
below. (2 pts) (REMEMBER FOR CURRENT MEASUREMENTS TO START WITH THE 10
AMP SETTING AND CHECK YOUR CURRENT LEVEL TO MAKE SURE IT IS NOT SO
LARGE THAT YOU WILL BLOW A FUSE.)
(f) From the above measurement, predict the current through Ryellow and record the value plus
error below. (2 pts)
(g) Draw a schematic circuit diagram showing how to directly measure the resistance of Rblue
using only the DMM. (3 pts)
(h) Measure the resistance of Rblue and record the value plus error below. (2 pts)
page 4
(i) Calculate the resistance with error of Ryellow from the previous data. Do not make any other
measurements. (Show all of your work.) (5 pts)
page 5
AC Measurement with an Oscilloscope
No error analysis is required for this section.
3. Set up the circuit shown with the function generator set to give a square
wave amplitude of a few volts. The capacitor is the green component with
the black stripe. Use the yellow resistor.
(a) Display the function generator output on one channel and the voltage
across the capacitor on the other channel of the oscilloscope. Adjust the
frequency and the oscilloscope controls so that you can measure the time
constant of the capacitor’s voltage decay. Record your operating frequency,
your voltage scale and your time scale in the space below. (3 pts)
(b) Draw your oscilloscope display of both channels on the grid below.
Your sketch must be labeled as a proper graph. When you are finished
with your sketch, hold up your hand to have it checked by the
instructor. To get full credit your sketch must match your display.
(5 pts)
Check _____________
(c) Using the DMM, measure the resistance of the yellow resistor. Record its value below. (2 pts)
page 6
(d) Determine and record the time constant of the capacitor discharge. Show explicitly how you
determined your value from the display on your oscilloscope. If you believe you display is
incorrect, show how you would have found the time constant if the display were correct to get
partial credit. (7.5 pts)
Hint: for a discharging capacitor:
VC  V0et /RC

(e) Determine the capacitance of the capacitor from your measured time constant. Again, even if
your display is wrong, show how you would find it to get partial credit. (2.5 pts)
page 7
Error Propagation Rules
0.7.1 Rule 1: A constant multiple
If
Y= k A
where k is a constant, then
Y = k A
0.7.2 Rule 2: Addition and Subtraction
If
Y=A±B±C
then
Y = (A)2 + (B)2+ (C)2 .
0.7.3 Rule 3: Multiplication and Division
If
Y = ABC, Y = ABC–1, Y = AB–1 C–1, or Y = A–1 B–1 C–1
then
2
2
2
Y
A 
   B 
   C 

 
 A   B   C 
Y
For multiplication and division we add the fractional (or percentage) errors.
0.7.4 Rule 4: Powers
If
Y = A, where  is arbitrary: integer, fraction, positive or negative
then
Y
A
=
||
Y
A
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