Q.What do you known about Cathode Rays? OR Write a detail note on Photoelectric Effect.

Cathode rays, produced in a low-pressure gas discharge tube, are streams of electrons travelling from the cathode toward the anode — their study (properties + charge-to-mass ratio) led directly to J.J. Thomson's discovery of the electron.

Answering: 'What do you know about Cathode Rays?'

Discovery/production: Cathode rays are produced when a high voltage is applied across two electrodes sealed in a glass discharge tube containing gas at very low pressure (around 10⁻⁴ atm). A stream of radiation is observed travelling from the cathode (negative electrode) toward the anode (positive electrode) — hence the name 'cathode rays'.

Properties:

1. They travel in straight lines from the cathode (demonstrated by the sharp shadow cast by an object placed in their path).
2. They cause a green fluorescent glow on striking the glass wall of the tube coated with a phosphorescent material like zinc sulphide (ZnS).
3. In the absence of an electric/magnetic field, they travel in straight lines, but they are deflected toward the positive plate in an electric field and follow a path consistent with negatively charged particles in a magnetic field (per the right-hand/Fleming's rule) — showing they are negatively charged.
4. They possess kinetic energy/momentum — they can rotate a small paddle wheel placed in their path, showing they consist of material particles, not just radiation.
5. Their characteristics (charge, e/m ratio) are the same regardless of the electrode material or the nature of the gas taken in the tube — showing that these particles (electrons) are a universal, fundamental constituent of all matter. …