Effect of electric fields on cathode rays (1 Viewer)

[mrpotatoed]

In physics dot point, the answers say that during the 1800's, scientists determined that electric fields had no effect on cathode rays. My understanding is that every scientist except Hertz determined that it did have a noticeable effect. So, not too sure what is going on here.

Also, do we have to call cathode rays, cathode rays? Or can we simply say electrons. EG: will you lose marks in a HSC exam for referring to cathode rays as simply electrons.

 

[anomalousdecay]

It would be "nicer" to use cathode rays in the context of experiments before they were found to be electrons. However I doubt you would ever lose marks for that.

 

[jordankime]

So in the early experiments on cathode rays, Hertz (among others) attempted to detect deflection of a cathode ray passing through an electric field generated by two electric plates. However, his experiment had a fundamental flaw in producing the electric field. To gain the necessary magnitude in the electric field to observe any deflection required very high voltages (Note that E=V/d) across the plates. But this in turn lead to ionisation of the small amount of gas still in the tube, allowing anions and cations to transfer charge between the two electric plates. This meant that current could flow between the plates and bought the plates back to near electrical equilibrium. As a result, the electric field was all but cancelled out and no deflection was detected in these experiments. So convincing was this that the scientific community, particularly in Germany, accepted it as a valid observation for many years. This was especially considering the results could be easily replicated and the obvious implications it had in support of a wave theory. The results were largely accepted at the time, and the repeatability of the experiment meant no one could dispute the result. It was probably the biggest setback to the British scientists as they tried to prove their particle theory, knowing that the accepted experimental evidence contradicted their theories.

It wasn't until Thomson came along that this issue was resolved when he noted a slight flicker when he turned on the electric field (this represented the time before the gas had fully ionised). He realised the fault in the previous experiments and rectified the issue through reducing the pressure even further to prevent ionisation. It was only then that he was able to show significant deflection of the rays by an electric field and prove that they were negatively charged. The British teams were then able to eliminate the largest flaw in their theories and convince the divided scientific community that their particle theory was accurate.

Hope that helps

 

[mrpotatoed]

So convincing was this that the scientific community, particularly in Germany, accepted it as a valid observation for many years. This was especially considering the results could be easily replicated and the obvious implications it had in support of a wave theory. The results were largely accepted at the time, and the repeatability of the experiment meant no one could dispute the result. It was probably the biggest setback to the British scientists as they tried to prove their particle theory, knowing that the accepted experimental evidence contradicted their theories.

My teacher said that it was only Hertz, and that the majority of the scientific community did find a deflection. But since Hertz was a respected scientist they were confused at the contradicting results. Or is my teacher wrong and none of them saw a deflection before Thomson?

 

[Kaido]

Uhh, the syllabus does not require you to specifically name scientists that observed/didn't observe the deflection. But your teacher is incorrect