Discovery Of The Electron - J.J Thompson Flashcards
Who discovered the electron?
J.J Thompson
What did J.J Thompson discover?
The electron
What did J.J Thompson investigate?
He investigated if the cathode rays discovered by Crookes consisted of charged particles
Describe the apparatus used in J.J Thompson’s experiment.
5
A vacuum tube
A negative and positive plate in the middle of the tube directly opposite each other (one on top/one on bottom)
A fluorescent screen at the far end of the tube
At the small side of the tube - a negatively charged cathode plate and a positively charged anode plate
The charges plates are parallel to each other (one at the beginning of the tube and one slightly further in)
There is a hole in the centre of the positively charged plate which allows the cathode rays to move through in a beam which strikes the fluorescent sheet at the far end
How did Thompson obtain a narrow beam of cathode rays?
By passing them through a small hole in the positive electrode
What happened if there was no charge on the parallel plates in the middle of the tube?
The beam of cathode rays passed straight down the tube and struck the fluorescent screen in the middle
What happened when there was a positive charge placed on the top plate?
The position of the spot on the fluorescent screen moved upwards
Under what conditions did the spot on the fluorescent screen move upwards?
When a positive charge was placed on the top parallel plate in the middle of the tube
What did Thompson conclude from his experiment?
He concluded that the cathode rays consisted of negatively charged particles
How could Thompson conclude that the cathode rays consisted of negatively charged particles?
Since the cathode rays were attracted upwards and unlike charges attract each other
What name was given to the negatively charged particles that make up cathode rays?
Electrons
Describe Thompsons’ second experiment.
2
He placed a large electromagnet outside the glass tube and adjusted the strength of the magnetic field
(Same apparatus as first experiment with the addition of an electromagnet)
What did Thompson find from his second experiment?
He found that the electrons were also deflected in the magnetic field
During his second experiment, what was Thompson able to do when using the magnetic field?
Using the magnetic field, he was able to bring the beam of electrons back down to its original position
What was Thompson able to calculate from the results of his second experiment?
(2)
He was able to calculate the ratio of the charge of the electron to its mass
Charge of electron/mass of electron
