THE
CATHODE RAY TUBE
A MODULE ON
ELECTRIC FIELDS AND fORCES
PRINCIPAL AUTHORS: Arnold Benton
American institute of Physics
Ludwig P. Lange
PROJECT DIRECTORS: Carl R. Stannard
Bruce E. Ma rsh
State University of New York
at Binghamton
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The purpose of this experiment is to give you a chance to see and learn ~or yourself some facts about electricity. Electric charges are a part of all ordinary ...
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THE
CATHODE RAY TUBE
A MODULE ON
ELECTRIC FIELDS AND fORCES
PRINCIPAL AUTHORS: Arnold Benton
American institute of Physics
Ludwig P. Lange
PROJECT DIRECTORS: Carl R. Stannard
Bruce E. Ma rsh
State University of New York
at Binghamton
Page
1
Electrostatic C.athode P,ay Tubereflection Beam of the
there are some things you should know and be able to do before
you begin. Try to answer the following questions. If you can
handle them all easily, you should be able to read the module
and do the experiments without difficulty. If you have trouble
with any of these questions, ask your instructor for help on
those items before you begin to study the module.
For the right triangle at the right:
(a) sin (^) e = (^3)
(b) cos e =
(c) tan e (^) = A man walks 4 miles east, then he walks 4 miles^4
point?
3. Write as a number between 1 and 10 mUltiplied by the
4. Carry out the indicated calculations:
3 x 1010 x 6 x 10-^27
9 x 10-^19
B. Vocabulary
- The following words are used in connection with forces on an object and the motion that may result. Can you define them? (a) force (f) velocity (b) attract (g) acceleration (c) repel (h) average (d) deflect (i) constant (e) mass (j) uniform
- The following words are used in connection with work done by a force and the changes in energy which may result. Can you define them? (a) work (e) conservation (b) energy (f) joule (c) kinetic energy (g) microjoule (d) potential energy
- The following words are used in connection with vectors. Can you define them? (a) vector (d) tangent (b) component (e) parallel (c) magnitude (f) perpendicular
- The following words are used in connection with elec- trical app[.ratus. Can you define them? (a) eleetri.city (f) oscilloscope (b) terminal (g) deflecting plates (e) electrode (h) banana plug (d) cathode (i) AC (e) battery (j) DC
The list of learning goals below should help your study of
the experiments, reading material, and problems included in
this module. If you are able to perform all of the tasks in
this list, you should have no trouble with the test that will
follow at the end of the module. You should be prepared to
1. Give the rules for attraction and repulsion of electric
2. Describe the transfer of electric charge from one body to
another and the effect of electric charge on metal surfaces.
3. Define electric field, electric intensity, potential differ-
ence or voltage.
4. State the names of the Standard International (5I) units for
all quantities that appear in the equations of this module.
- Use the law F = (KQlQ2)/r2 and the expression F = qE to
solve problems.
6. Discuss the properties of field lines and equipotential
surfaces and tell why they intersect at right angles._
7. Determine the path of a charged particle that enters a
electric field perpendicular to the field.
8. Calculate the final kinetic energy and velocity of a charged
particler given the initial velocity and the potential
difference through which it moves.
9. Measure, using the apparatus of laboratory expe:r-irnent3, the
deflection of an electron beam on the face of a CRT as a
function of the voltage on the deflecting plates.
protects the other parts and keeps them in a vacuum. The
electron gun does three things: It supplies electronsl, accel-
rapidly along closely spaced horizontal lines to cover the entire
screen. At the same time the brightness or intensity of the spot
shade of whi t:e, black or gray. The brightness or intensity
depends on the number of electrons striking the screen per
An electron is the smallest charged particle radius
less than 10-14^ meters, mass 9.11 x 10-31^ kg, and negative
charge 1.60 x 10-19^ coulombs.
BASE SCREEN
V"
ELECTRON GUN (^) DEFLECTING PLATES
DEFLECTING PLATES
Nurses can watch the electrical pulses produced by cardiac patients' hearts on the cathode ray tube monitors located in a central display panel.
A general purpose physiological monitor which displays eight traces on the large cathode ray tube. Three channels display electrocardiographchannels display heart traces, sounds, two two are for intercardiac pres- sure, and one is a channel for DP/DT.
Photographs courtesy of Wilson Memorial Hospital, Johnson City, New York
OBJECTIVES
- To study the effect of electric charge on a piece of metal.
- To study the effect of electric charge on the electron beam of a cathode ray tube.
Have you ever walked across a rug and gotten a shock when you touched another person? Have you ever run a comb through your hair and noticed that the comb will pick up small pieces of paper? Have you ever noticed nylon clothing cling and some- times crackle as you take it off? If your answer to any of these questions is yes, you have observed electric charges "doing their thing." The purpose of this experiment is to give you a chance to see and learn ~or yourself some facts about electricity. Electric charges are a part of all ordinary matter. There are two kinds of charge called positive and negative. The things we use, see, and touch in our daily lives have equal numbers of positive and negative charges in them. They are said to be "neutral" or uncharged. Sometimes, when things are rubbed together a separation of charge takes place. For example, when a plastic rod is rubbed with a wool cloth, the plastic rod ends up with more negative charge and the wool cloth with more posi ti.ve charge than before. They are nO'i said to be charged -- one negatively and the other positively. Charges within neutral objects can also be separated under some conditions. Thus it is possible for negative charges in an object to move
you how to operate it. If you use the CRT of the module,
start with the DC switch on STANDBY. Turn the AC power
to ON. Focus the beam by adjusting the Band C voltages
on the power supply. If the bright spot doesn't appear on
deflection permanent or pulse-like?
(d) Connect a 22~ volt battery to one pair of deflection
plates. Is the deflection permanent?
GRH ,/
..:ow~ SUPPLY
FIG.
FIG.
The signalsray tube in franthe Bre>c:mCthe radarCounty Airport scanner are controldisplayed tcMer. on this cathode
This picture of an older radar display tube, fonnerly used in the radar roc.rnof the BroomeCounty Airport, sha.vs the cathode ray tube and scree of the electronics. associated with a radar display systan. Photographs courtesy of Federal Aviation Administration and
small charged spheres. Coulomb found that the force depends' on (1) the amount of charge on each sphere, and (2) the distance between them. Keeping the distance between the charges the
are kept the same? Coulomb found that doubling the distance between the charges made the force one-quarter (1/4) of what it was. When the distance was made M times as large, the force became 1/M^2 of what it was. The way the force changes with the
be written in a formula. If F is the force, Q 1 and Q 2 the magnitudes of 'the charges, and r the distance between them, the
Ql and Q 2 are in coulombs, abbreviation -- C r is in meters, abbreviation -- m K = 9.0 x 109 N m^2 /c^2 (for charges ,in air or vacuum)