Physics
Transmission Coefficient
Quick fact
The transmission coefficient can be greater than 1 for certain quantum tunneling scenarios, where particles have a probability of passing through a barrier despite lacking classical energy.
Why this is interesting
Imagine you shine a flashlight at a water surface—why does some light pass through while the rest bounces back? The answer lies in a simple ratio called the transmission coefficient.
Read the full explanation
Understanding Transmission Coefficient
When a wave (like light, sound, or a water ripple) encounters a boundary between two different materials, part of its energy is reflected and part is transmitted into the new material. The transmission coefficient (T) is defined as the ratio of transmitted wave intensity to incident wave intensity. It ranges from 0 (no transmission, full reflection) to 1 (full transmission, no reflection). For example, when light travels from air into glass, about 96% is transmitted and 4% is reflected at a normal incidence. The coefficient depends on the properties of both media, such as their refractive indices for light or acoustic impedances for sound.
A deeper explanation
The transmission coefficient arises from the conservation of energy at the boundary. For a wave, the sum of reflected and transmitted energy must equal the incident energy. It is mathematically linked to the reflection coefficient (R) by T + R = 1 for lossless media. In wave physics, the coefficient is derived from boundary conditions requiring continuity of wave amplitude and its derivative. For light, Fresnel equations give T based on polarization and angle of incidence. In quantum mechanics, the transmission coefficient explains tunneling—where particles cross barriers despite insufficient energy—a key principle in phenomena like radioactive decay and scanning tunneling microscopes. Understanding T is vital for designing antireflective coatings, acoustic insulation, and quantum devices.