This lesson introduces quantum tunneling and explains why it differs from motion in classical mechanics. It establishes the potential-barrier model used throughout the unit.
In classical mechanics, a particle with total energy less than a barrier's potential energy cannot pass over it. For example, a ball with 100 J of energy cannot cross a hill that requires 200 J; it turns back. The probability of crossing is zero in this idealized description.
All flashcards
What is the transmission coefficient for a particle incident from the left?
T=∣F/A∣2, the transmitted intensity divided by the incident intensity.
What does β describe inside a square barrier when E<U0?
The inverse-length parameter controlling the exponential variation of the wave function inside the barrier.
What is field emission?
Electron escape from a conducting surface by tunneling through a barrier narrowed by an external electric field.
How does a scanning tunneling microscope map a surface?
It scans a conducting tip and uses the position-dependent tunneling current to infer surface features.
What produces resonant tunneling in a quantum-dot device?
Efficient transmission when an outside electron's energy aligns with a discrete energy level in the dot.
Quiz questions
For a particle incident from the left, which expression gives the transmission coefficient in terms of incident amplitude A and transmitted amplitude F?Answer: ∣F/A∣2
At a finite step in a one-dimensional potential, which quantities are continuous for a physically acceptable wave function?Answer: The wave function and its first spatial derivative
What does a scanning tunneling microscope measure as its tip moves across a conducting surface?Answer: Tunneling current that varies with tip-to-surface separation
In a resonant-tunneling device with a quantum dot, when is transmission most efficient?Answer: When an outside electron's energy aligns with an allowed dot energy level
For alpha decay, what is the usual effect of increasing the alpha-particle energy?Answer: It reduces the outer turning distance and narrows the effective barrier
Based on University Physics Volume 3 by Samuel J. Ling, Jeff Sanny, William Moebs (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.