Lab 3 Electron Beam Deflection by Electric Fields
Team members:
Ivan Williams, Justin Campbell, Drew Curto
Task 1
Use the Wolfram demonstration
Insert a graph here that shows the relationship between the acceleration and the initial x-velocity for
fixed deflecting voltage. What is the relationship? Does it make sense in terms of what went into
deriving the equation for deflection?
They are proportional, as initial velocity increases the acceleration must increase in order to
maintain constant deflection. This makes sense because to maintain a constant deflection the
change in velocity in the x direction over the change in velocity in the y direction must remain
constant. The above graph depicts the change in acceleration over the change in velocity in the
x. Since the change in acceleration is equal to the change in velocity in the y over the change in
time, where the change in time is inherently constant the change in acceleration over the
change in velocity in the x (the initial velocity) is also constant.
Study the cutout
Do the upper deflectors move the beam spot along the x axis
We found the ao for the upper and lower deflectors from the measurement, from this we
realized that the lower deflector has a higher ao and the upper deflection has a lower ao. Then
we found the aoy and aox from the inverse of the voltage vs the slope and found that aoy was
larger than aox. Since the lower deflector has a higher ao, it must deflect in the y direction and
thus the upper deflector moves along the x axis.
Calculated values for a0: Show the parameter values used to calculate the constants a0.
Circle the directions, X or Y.
Upper deflectors
Deflection Direction?
L=
d=
15 mm
12.59
mm
x
Lower deflectors
Deflection Direction? y
L=
d=
15 mm
8.25
-1-
mm
D=
110
mm
Calculated ao =
65.53
D=
135
mm
mm Calculated ao =
112.72
mm
Task 2
Data: Measure and plot the x and y deflections due to different values of the voltages V1 and
V2, using V2x = V2y.
1/V1 = .0045 V-1
V1 = 219 V
Slopes (mm/V)
V2 x = V2 y
(Volts)
x
y
(mm)
(mm)
+15
65
34
0
55
52
22
71
1.43
-1.23
1/V1 = .0033 V-1
V1 = 300 V
Slopes (mm/V)
V2 x = V2 y
(Volts)
x
y
(mm)
(mm)
+15
60
39
0
45
53
-15
27
65
1.2
-.866
1/V1 = .0038 V-1
V1 = 260 V
Slopes (mm/V)
V2 x = V2 y
(Volts)
x
y
(mm)
(mm)
+15
63
37
0
45
53
-15
25
69
a 0 x = 192 mm;
1.26
-1.06
a 0 y = 303 mm
Considering the actual geometry of the deflector plates, would you expect the measured value
to be equal to, larger than, or smaller than the calculated values? Explain! Did you observe this?
-2-
We expected the measured value to be larger because the deflector plates are flared and we
did in fact observe this.
-3-