|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Electrons
Q7 The value of the charge to mass
ratio was determined by placing an electron gun into sealed glass
vessel containing an inert gas, like
argon. As electrons
are fired they light up the gas (due to promoting electrons in the gas,
which then de-excite and release a photon) . If placed inside a magnetic
field the electron will circle around inside the vessel, causing a ring.
A scale is placed inside. |
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
Analyses
Applying conservation of energy
Ke = Energy due to voltage
0.5mv2 = Ve
(1)
Circle forces
F(circle)
= F(magfield)
mv2/r
= Bev
So v =Ber/m
(2)
Placing 2 into 1
0.5m(Ber/m)2 = Ve
0.5B2er/m = V
e/m = 2V/B2r2 |
|
|
|
|
|
|
|
|
|
|
|
|
|
| The
potential V can be measured directly using a voltmeter and the radius of
the circle from the scale in the vessel. The field strength though
can only be inferred from the current in the coil and the distance of the
coil to the electron beam, so the value e/m can only be estimated. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The
value of the charge of an electron was determined by suspending a charged
oil drop in an electric field. This was done by giving the drop a
slight negative charge and placing it between two charged plates.
Only when the upward force due to the field was equal to the weight of
the drop would the drop levitate.so
F(gravity) = F(electric)
mg = Eq
mg = Vq/d
q = V/dmg
V is potential
difference
d is the plate
seperation
m mass of droplet
g gravitational
field strength
q charge on
the droplet
By repeating the experiment Millikan showed
the charge on the oil drop was always a multiple of a number, the charge
of the electron (since you can only have integer values of number of electrons) |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Q10
l
= hc
[T(T + 2mc2)]
If an electron has 10eV of kinetic energy then
[T(T
+ 2mc2)] = [1.6*10^(-19)
(1.64*10^-13)]
5.122*10^-16J
l
= 1.989*10-25
5.122*10^-16
3.9*10^-10m
Q12 Electrons are treated as particles when
dealing with beta decay and deflections due to magnetic and electric fields
Electrons are thought of as waves when it
comes to finding them in atoms. The wave model gives probabilities
of finding the electron at different locations where an electron cloud
model is used.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Back To The Top
|
|
|