THOMSON'S EXPERIMENT

[sherlock2308]

Can anyone tell me about thomson's experiment and also in the millikan's experiment how was the oil droplet charged?

[Confusions allowed]

First, make clear what are you trying to say. Also, the lecture notes are there.

[sherlock2308]

cathode rays are defined as the rays produced by the cathode when heated in low pressure. Why is the low pressure factor important? would vacuum do?

[Keep Guessing!]

Sir told that in class already. Low pressure ensures less gas atoms so that the electrons don't encounter too many collisions.

[sherlock2308]

Vacuum has no gas atoms!!! Won't it be better then?

[Aasim Saifee]

Vacuum has no gas atoms!!! Won't it be better then?

it is not possible to create perfect vacuum.

[Keep Guessing!]

And we need a gas to ionize. Also, wikipedia says that another reason for him to decrease the pressure was to get better readings and a more accurate value of the e/m ratio.

[The Confused Guy (O.o)?]

For perfect vacum u can go to space and try the experiment :v (jk) and send me the results if u succeed

[The Confused Guy (O.o)?]

And we need a gas to ionize. Also, wikipedia says that another reason for him to decrease the pressure was to get better readings and a more accurate value of the e/m ratio.

Infact u dont need gas to ionise to give electrons , the electrodes themselves can release electrons under high electric field, heat or light

[Sreejith A Nair]

To answer this question we need to know the proportion of cathode ray produced from the cathode and the gas in the tube. This could be verified by a series of experiments in which the pressure of the tube is reduced continuously until we get as close as possible to vacume. All the experiments should be conducted at a constant potential difference. With only the pressure changing. Since we are not in a state to cundect such an experiment logical explanations are satisfactory. And I suppose that the major source is the cathode itself as it is highly unlikely that such a small amount of gas produces enough electrons to produce respectable florasence
. If any one has oppositions please point out.

[Keep Guessing!]

The electrons in the cathode ray are from the cathode plate. But first the gas is ionized by the high electric potential. The ions thus formed get attracted to the cathode, collide with it, and release electrons from the cathode. So we do need a small amount of gas to kind of start the emission. However, this was in the olden times. In modern CRTs, thermionic emission through filament is used.

But, I have a question- when the gas atoms are initially ionized, it happens because of the high electric potential across the electrodes. Why isn't the metal ionized before the gas? We all know that the ionization energy of metals is generally lower than gases.

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