Discovery of cathode rays

Discovery of cathode rays

Discharge tube experiments:

Structure:

1.A cylindrical glass tube about 50 cm long, closed at both ends called the discharge tube

2.The tube is fitted with two metallic electrodes, which are connected to a source of high voltage

3.It is filled with gas and the discharge tube is connected to a side tube, through which the gas can be evacuated to any desired pressure with the help of a vacuum pump

Observations:

-As the pressure is reduced to a certain value (0.01  0.001 mmHg) and the potential difference increases up to 10000 volt: There will be a flow of invisible rays emitted from cathode and causing glow behind the anode. These rays are called cathode rays. These rays were named as cathode rays because their point of origin was the cathode

Properties of cathode rays:

1.Travel in a straight line

2.Negatively charged electrons

3.Affected by the presence of a magnetic field and electric field

4.Particulate in nature

5.When stopped they produce X-rays

6.Has a thermal effect

7.Doesn't change by changing either cathode material or kind of gas

Conclusion:

•Particles is a universal component of matter

•Cathode rays consist of negatively charged particles called electrons

•Cathode rays exist in all matters

Note: to get the cathode ray, the tube discharged to very low pressure and connected to high potential difference G.R because gases don't conduct electricity under normal conditions

Thomson's atomic model:

1. Atoms consisted of a large massive sphere positively charged body with a number of small negatively charged electrons scattered throughout it

2. The total charge of the electrons exactly balanced the positive charge of the large mass, so the total electric charge was zero