Laboratory Practices

Families of practices by physical domain and experimental reading of theoretical concepts.

General idea of the topic

Physics laboratory practices bring together the historical and foundational experiments that established classical and quantum physics: determining Newton's gravitational constant $G$, the speed of light $c$, the photoelectric effect, the electron charge-to-mass ratio ($e/m$), and electron wave diffraction. Conducting these experiments bridges theoretical formulas and empirical reality, illustrating how fundamental physics was uncovered and how experimental challenges were mastered.

This node covers the reversible Kater's pendulum, Cavendish torsion balance, Millikan oil-drop experiment, photoelectric determination of Planck's constant $h$, and Michelson optical interferometry.

What you will truly understand

You will understand how Millikan's oil-drop experiment proved charge quantization by balancing electrostatic forces $qE$ against gravitational forces corrected for buoyant air forces and Stokes' viscous drag.

You will measure Planck's constant $h$ from the stopping potential $V_0$ of emitted photoelectrons as a linear function of incident photon frequency ($e V_0 = h f - W$).

Recommended learning route

1. Mechanics and gravitation: Kater's pendulum for high-precision local $g$ determination, and Cavendish torsion balance.
2. Electromagnetism: current balance for $\mu_0$, Thomson cathode-ray tube for electron $e/m$ ratio, and Faraday induction loops.
3. Optics and interferometry: Michelson interferometer for sub-micron wavelength measurements and air refractive index, and single/double slit Fraunhofer diffraction.
4. Quantum and atomic physics: photoelectric effect ($h/e$ slope), Franck-Hertz inelastic electron collision spectroscopy, and De Broglie electron diffraction in polycrystalline graphite.

Physical criterion you must acquire

Isolating non-ideal physical effects in classical apparatuses (air resistance damping, contact resistance, Earth's ambient geomagnetic field) and implementing experimental compensation techniques.

Connection with real problems

• Laser interferometry in gravitational wave detectors (LIGO/Virgo).
• Photovoltaic solar cell characterization and photodetector response engineering.
• Transmission Electron Microscopy (TEM) utilizing relativistic De Broglie matter waves.

Final goal of the topic

Master the setup, execution, calibration, and data analysis of landmark canonical experiments in classical, electromagnetic, and quantum physics.