Example: Transistors Transistors, fundamental components in modern electronics, rely on the manipulation of electron flow in semiconductors. In a bipolar junction transistor (BJT), electrons (or holes) are controlled by the application of voltage to different regions of the semiconductor, enabling the transistor to act as an amplifier or switch. The precise control of electron movement allows for the operation of complex electronic circuits in computers and other devices.

Example: Transmission Electron Microscope (TEM) In a transmission electron microscope, electrons are transmitted through an ultra-thin sample, and their interaction with the sample produces an image. TEM can achieve resolutions down to atomic scales, allowing scientists to visualize the arrangement of atoms in materials such as graphene or biological cells. This high resolution is due to the much shorter wavelength of electrons compared to visible light.

Example: Einstein’s Experiment In Einstein’s experiment on the photoelectric effect, light shining on a metal surface causes the ejection of electrons from the metal. The experiment showed that the kinetic energy of the emitted electrons is proportional to the frequency of the incident light, not its intensity. This demonstrated the quantized nature of light and led to the development of quantum mechanics, confirming the particle nature of photons.

Example: Hydrogen Atom Spectrum When an electron in a hydrogen atom absorbs energy, it moves to a higher energy level (excited state). When it falls back to a lower energy level, it emits light at specific wavelengths. These wavelengths form discrete lines in the atomic spectrum of hydrogen, known as the Balmer series in the visible range. This emission spectrum is a result of the quantized energy levels of electrons and provides key evidence for the Bohr model of the atom.