Quantum Physics

According to de Broglie's hypothesis, every moving particle exhibits wave-like properties, with an associated wavelength known as the de Broglie wavelength. For a particle having momentum , where is its mass and its velocity, the de Broglie wavelength is given by: where is Planck's constant ( ). This relationship shows that the wavelength is inversely proportional to the momentum of the particle, linking particle and wave nature.

A photocell operates based on the photoelectric effect, which occurs when light of sufficient frequency (or energy) shines on the surface of a material, typically a metal. The energy from the incident photons is absorbed by the electrons in the material. If this energy exceeds the material's work function (the minimum energy required to free an electron), electrons are emitted from the surface. These emitted electrons produce a current when collected, and this current varies with the intensity and frequency of the incident light. Thus, a photocell converts light energy into electrical energy using the photoelectric effect.

Cathode rays are streams of electrons emitted from the negative electrode (cathode) in a vacuum tube. When a high voltage is applied across the electrodes in the vacuum tube, electrons are emitted from the cathode due to thermionic emission and accelerated towards the anode. These electrons travel in straight lines and can be deflected by electric and magnetic fields, confirming their charged particle nature. Cathode rays were fundamental in discovering the electron and understanding its properties.