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Instructions: Before lab, read the required reading from the textbook and the laboratory in its
entirety. In your lab notebook, respond to the warm up questions and derive a specific prediction
for the outcome of the lab. During lab, compare your warm up responses and prediction in your
group. Then, work through the exploration, measurement, analysis, and conclusion sections in
sequence, keeping a record of your findings in your lab notebook. It is often useful to use Excel to
perform data analysis, rather than doing it by hand. A t the end of lab, disseminate any electronic
copies of your results to each member of your group.
Read : Tipler & Mosca Chapter 21 Section 216 and review Chapter 3 Sections 31 & 32. EQUIPMEN T
You h ave a C athod e Ray Tube (CRT), Cenco CRT
p ow er supply, banana cables, DMM and shield ed
b anana cables. The fluorescent screen has a one half centim eter grid w ith m illim eter hash m arks in
so t hat y ou can m easu re the position of t he beam
o n the screen. Read the section Cathode Ray Tube and A ccessories in the Equipment a ppend ix.
Read the append ices S ignificant Figures , A ccuracy, Precision and Uncertainty, a nd
Review of Graphs t o help you take d ata effectively.
If equipment i s missing or broken, submit a problem report by sending an email to
l abhelp@physics.umn.edu . Include the room number and brief description of the
p roblem. 19 GRAVITATIONAL FORCE ON THE ELECTRON – 1302Lab1Prob3 WARM UP
1. D raw a p icture of the CRT in the hor izontal position. Do not includ e the d eflection
plates show n in the append ix d iagram s since they w ill not be used in this lab. D raw
the electron's trajectory from the tim e it leaves the electron gun until it hits the screen.
Label each im portant kinem atics quantity in the problem . Using a free bod y d iagram ,
label all forces on the electron d uring this tim e. Choose a convenient coord inate
system and p ut it on your d raw ing. Does the vertical com ponent of the electron's
velocity change? Why or w hy not? Does the horizontal com ponent of its velocity
change? Why or w hy not?
2. C alculate the velocity of the electron just after it leaves the electron gun.
H int: The change in the electric potential energy of an electron m oving across a pair of
acceleration plates is the voltage d ifference betw een the tw o plates tim es the electron's
charge. What basic physics principle can you use to calculate the electron’s velocity as
it exits the electron gun? What assum ptions m ust you m ake to carry out this
calculation?
3. W hat physics principle(s) can you use to calculate how far the electron falls below a
straightline trajectory d ue to the force of gravity? What quantities m ust you know to
m ake the calculation? Perform this calculation to find a sym bolic and then a num erical
answ er.
4. D oes your solution m ake sense? You can check by estim ating the tim e of flight of the
electron based on its initial velocity and the distance betw een its starting point and the
screen. In that am ount of tim e, how far w ould a ball d rop in free fall? If the solution
d oes not m ake sense, check your w ork for logic or algebra m istakes.
5. Repeat 14 for a CRT pointed d irectly upw ard s, find ing first a sym bolic and then a
num erical answ er.
6. Finally, repeat 14 at an arbitrary inclination angle from the horizontal. State your
a nsw er sym bolically and then num erically (a num ber tim es a function of the
inclination angle, in this case).
IMPORTAN T hints: (1) Try using a reference fram e w here x is always along and y is
alw ays perpend icular to electron’s initial trajectory. (2) If your equations becom e
com plicated , m ake u seful approxim ations by consid ering how large any term that
contains the electron’s velocity is to other term s in a given equations. (3) Does your
arbitrary angle answ er com port w ith the strictly horizontal and strictly vertical cases? 20 GRAVITATIONAL FORCE ON THE ELECTRON – 1302Lab1Prob3 PRED ICTION
D eterm ine the physics task from the problem statem ent, and then in one or a few
sentences, equations, d raw ings, and / or graphs, m ake a clear and concise pred iction
that solves the task. (H int: H ow can you m ake a qualitative prediction w ith as m uch
d etail as possible?) EXPLORATION
WARN IN G: You w ill be w orking w ith equipm ent that generates large electric
v oltages. Im proper use can cau se painful bu rns. The p ow er m u st be turned o ff a nd
y ou m u st w ait a t least one m inute before any w ires are d isconnected from or
connected to the pow er supply. N ever touch the cond ucting m etal of any w ire .
Follow the d irections in the append ix for connecting the pow er supply to the CRT.
Check to see that the connections from the pow er supply to the high voltage and the
filam ent heater are correct, before y ou turn the pow er supply on. You should have a
difference o f ~250500 Volts of electric potential betw een the cathod e and anod e. After a
m om ent, you should see...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
 Spring '14

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