Discovery of the Electron 2 Flashcards
How are cathode rays produced in a discharge tube?
If voltage applied to the tube is high enough, some of the gas atoms are ionised.
Positive ions created near the cathode surface are attracted to the cathode. Photons are emitted when some of the ions and electrons produced by ionisation recombine.
Some electrons do not recombine and move towards the anode. This causes excitation by collision of gas atoms. Photons are emitted when the atoms de-excite.
What were J.J. Thomson’s conclusions about cathode rays?
They have energy, momentum and mass.
They are negatively charged.
They have the same properties, regardless of what gas is used.
What is thermionic emission?
Thermionic emission can produce electrons without a gas.
When a metal is heated, some of the free electrons gain enough kinetic energy to leave the metal surface. The electrons can be accelerated by an electric field.
What affects the speed of the electrons produced in thermionic emission?
Increasing the potential difference increases the force attracting the electrons towards the anode.
This results in the electrons gaining higher speed.
How can you calculate the specific of an electron?
Using a magnetic field:
r = mv/Be
e/m = v/Br
What was the significance of the specific charge of an electron?
Thomson showed that electron specific charge is 1.76 x 10^11 C/kg
This was 1860 times larger than that of a hydrogen ion, which was the largest specific charge known at the time.
Describe Millikan’s oil drop experiment.
Controlled the motion of charged oil droplets using the electric field between oppositely charged parallel plates.
Made any charged droplet stay stationary by adjusting the potential difference between the plates until the electric force was equal and opposite to the weight of the droplet.
