write note on Discorvery of Electron
Answers
Answer:
Thomson constructed a glass tube which was partially evacuated i.e. much of the air was pumped out of the tube. Then he applied a high electrical voltage between two electrodes at either end of the tube. He detected that a stream of particle (ray) was coming out from the negatively charged electrode (cathode) to positively charged electrode (anode). This ray is called cathode ray and the whole construction is called cathode ray tube. The schematic of a cathode ray tube is given in figure 2.
Figure 2. Cathode ray tube
Properties of cathode ray particle
1. They travel in straight lines.
2. They are independent of the material composition of the cathode.
3. Applying electric field in the path of cathode ray deflects the ray towards positively charged plate. Hence cathode ray consists of negatively charged particles.
Figure 3. Deflection of cathode rays towards positively charged plates
J. J. Thomson measured the charge-by-mass-ratio (e/m) of cathode ray particle using deflection in both electric and magnetic field.
e
m
=
−
1.76
×
10
8
coulomb per gram
The cathode ray particle turned out to be 2000 times lighter than hydrogen.
Although we got e/m ratio for electron from J.J. Thomson’s Cathode Ray Tube experiment, we still don’t know the exact charge (e) for electron. American physicist Robert Millikan designed an experiment to measure the absolute value of the charge of electron which is discussed below.
Answer:
The Electron was discovered in 1896, by the British physicist J. J. Thomson, using a cathode rays while doing discharge tube experiments. Thomson also determined e/m, ratio of the charge e to the mass m of the material particle which constituted these rays.These protons add the overall positive charge of a molecule.