Wave-Particle Duality Flashcards
(18 cards)
What is wave-particle duality?
Wave-particle duality is the concept that waves can exhibit particle-like behavior and particles can exhibit wave-like behavior.
What evidence supports the particle nature of light?
The photoelectric effect; if light were purely a wave, electrons would be emitted at any frequency and not instantaneously.
What experiment supports the wave nature of particles?
Electron diffraction experiments demonstrate the wave nature of particles like electrons.
What was Newton’s stance on the nature of light?
Newton supported a particle theory of light (corpuscles) and believed particles accelerated in denser media to explain refraction.
Who opposed Newton’s theory, and what did he propose?
Christian Huygens proposed that light behaves as a wave, particularly due to the phenomenon of diffraction.
Why was Newton’s corpuscle theory ultimately flawed?
He believed light particles had mass, which is incorrect, although light does exist in quantized packets (photons), which behave differently.
What was James Clerk Maxwell’s major contribution to understanding light?
He theorized and later proved that light consists of two perpendicular oscillating fields—electric and magnetic—linked intrinsically.
How did Maxwell calculate the speed of light?
Using the permittivity and permeability of free space: c = 1 / (ε₀μ₀) = 3 × 10⁸ m/s.
How did Hertz demonstrate the existence of electromagnetic waves?
By observing sparks induced in a loop due to oscillating EM fields, and using standing wave patterns to measure their wavelength.
What did Hertz’s dipole antenna experiment prove?
The transverse and polarized nature of EM waves; no sparks occurred when the dipole was rotated 90°, confirming polarization.
Why can’t traditional glass lenses be used in electron microscopes?
Electrons are charged particles, so magnetic lenses must be used to focus and control their paths.
What is the principle behind the Transmission Electron Microscope (TEM)?
Uses magnetic lenses to focus electrons through a thin sample. Dense areas allow fewer electrons through, creating contrast.
Why is electron diffraction a problem in TEMs, and how is it mitigated?
Electrons diffract due to their wave nature, potentially blurring the image. Additional magnetic lenses refocus diffracted electrons.
How is the de Broglie wavelength of an electron calculated?
Using λ = h / p or λ = h / (2mₑeV), where V is the accelerating voltage.
Why are high-speed electrons desirable in electron microscopy?
Higher speed means shorter wavelengths, reducing diffraction and improving image resolution.
What is quantum tunneling in the context of Scanning Tunneling Microscopes (STM)?
Electrons can ‘tunnel’ across a very small gap (~1 nm) from sample to probe due to wave behavior and probability, even without enough classical energy.
How does an STM measure surface topography?
By measuring the tunneling current that varies with distance between the probe and sample—greater distance = less current.
What are the two modes of operation in STM?
Constant height: Measure changes in current.
Constant current: Adjust probe height to maintain constant current, mapping the surface.
