Ch 11 - DUAL NATURE OF RADIATION AND MATTER12th Physics

Nature: Cathode rays are streams of fast-moving, negatively charged particles (electrons) emitted from the cathode in a low-pressure discharge tube.

Specific Charge ($e/m$): Thomson found the value to be exactly $1.76 \times 10^{11} \text{ C/kg}$.

Universal Nature: Crucially, this $e/m$ ratio was found to be strictly independent of the nature of the cathode material or the gas used in the tube, proving that electrons are fundamental, universal constituents of all matter.

Straight Line Travel: They travel rapidly in straight paths, casting sharp shadows of objects placed in their way.

Heating Effect: They carry significant kinetic energy and produce heat upon striking metal surfaces.

Penetration: They can easily penetrate extremely thin gold or aluminum foils without puncturing them.

Fluorescence: They cause specific compounds (like those on a photographic plate) to exhibit phosphorescence and fluorescence.

X-Ray Generation: When they strike heavy targets with high atomic weights, they produce continuous X-ray spectra.

Observation: Millikan precisely measured the charge on suspended oil droplets and found that it was always an integral multiple of an elementary base charge.

Conclusion: This conclusively established the Quantization of Electric Charge. The elementary charge ($e$) was measured to be approximately $1.602 \times 10^{-19} \text{ C}$.