2.
J.J.'s experiment
J.J.
Thomson realised that he could deflect the cathode rays
in an electric field produced by a pair of metal plates.
One of the plates was negatively charged and repelled
the cathode rays, while the other was positively charged
and attracted them. Hertz had not been able to do this
because he had left too much gas in his discharge tube.
The
gas in Hertz's tube had become ionised by the electric
field produced by the plates. The positive ions moved towards the
negative plate and the negative ions towards the positive plate.
The net charge on the plates was therefore reduced and so the
strength of the electric field was reduced. The remaining electric field
deflected the cathode rays very little or not at all.
When
he repeated the experiment Thomson removed more of the gas
from his tube thus producing a much better vacuum. When
he passed the cathode rays through an electric field
a deflection did occur.
The
cathode rays moved towards the positively charged plate so the
rays must be negatively charged.
Next
Page
|
