Download Experiment 3.3 Thomson Experiment Aim To use a computer

Experiment 3.3 Thomson Experiment
Aim To use a computer simulation to analyse Thomson’s experiment.
http://www.hscphysics.edu.au/resource/template.swf
Algebra practice
1. Equate the equation for electric
force with the equation for
magnetic force to derive an
expression for the velocity of a
charged particle
2. Equate the equation for
magnetic force with the equation
for centripetal force amd to
derive an expression for the
charge to mass ratio for a
charged particle
3. Substitute the first derived expression
into the second derived expression and
simplify for an expression for the charge
to mass ratio for a charged particle.
In this step Magnetic field and electric field were both on and adjusted until the beam shows zero net deflection.
Record the magnetic field produced by the coils ................................. = ........................................ T
Record the voltage applied to the parallel plates. .....................................
Calculate the magnitude of the electric field
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When there is zero net deflection, the electric force on the beam in one direction is equal to the magnetic force on
the beam in the opposite direction. Therefore we can equate the two forces.
Equate the electric force with the magnetic force and determine the velocity of the particles.
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In this step The Electric field was left on, the magnetic field turned off and the radius of beam path measured.
Record the radius of the beam ...............................
The magnetic force on the beam is providing a centripetal force for the circular path. Therefore we can equate the
magnetic force with the centripetal force on the beam.
Equate the equation for magnetic force with the equation for centripetal force and rearrange so that q/m is on one
side of the equation
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Substitute value from the experiment into this expression to calculate the charge to mass ration for an electron
Value from above 
v= ....................................., E = ..........................................., B= ............................................
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Use your data sheet to calculate the q/m ratio of an electron to comment on the validity of the sumilation result.
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Calculate the charge to mass ratio for the following results in the same experiment as above. (show working)
For (c) you are to use the simulation at home to cllect a set of values and calculate the charge to mass ration for an
electron.
(a)
(b)
(c)
Voltage applied
to plates (V)
11.8
55
Magnetic field
applied (T)
183
835
Radius of
path (m)
0.412
.090