1. Discovery of Electron :
- “Like charges repel each other and unlike charges attract each other”.
- Michael Faraday showed that if electricity is passed through a solution of an electrolyte, chemical reactions occurred at the electrodes, which resulted in the liberation and deposition of matter at the electrodes.
- Cathode rays start from cathode and move towards the anode.
- Not visible
- Can be observed via fluorescent or phosphorescent.
- In the absence of electrical or magnetic field, these rays travel in straight lines.
- Consist of negatively charged particles, called electrons.
- Characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.
- Thus, we can conclude that electrons are basic constituent of all the atoms.
2. Charge to Mass Ratio of Electron :
- J.J. Thomson measured the ratio of electrical charge (e) to the mass of electron (me ) by using cathode ray tube and applying electrical and magnetic field perpendicular to each other as well as to the path of electrons.
- Thomson argued that the amount of deviation of the particles from their path in the presence of electrical or magnetic field depends upon
- Magnitude of the negative charge on the particle, greater the magnitude of the charge on the particle, greater is the interaction with the electric or magnetic field and thus greater is the deflection.
- The mass of the particle — lighter the particle, greater the deflection.
- the strength of the electrical or magnetic field — the deflection of electrons from its original path increases with the increase in the voltage across the electrodes, or the strength of the magnetic field.
3. Charge on the Electron :
- R.A. Millikan - oil drop experiment - to determine the charge on the electrons.
