Author: haroonkhan

De Broglie’s critics argued that the results from electron-diffraction experiments may indicate an undulating interaction between electrons, so these experiments didn’t decisively prove that electrons are waves when studied by diffraction. Definitive proof would still have to wait until technology advanced to make it possible to conduct the double-slit experiment with individual electrons. In one of his…

Experimental confirmation of de Broglie’s formula came in 1927, when G. P. Thomson at the University of Aberdeen and C. J. Davisson with L. H. Germer at Bell Labs observed diffraction—a typical wave-like behavior—from an electron beam. Unlike photons, electrons have a rest mass, and are thus perceived as “solid” particles. Electrons are negatively charged…

Bohr was able to explain the discrete spectral lines emitted by the hydrogen atom by forcing the electrons into a limited number of permitted orbits (Figure 94a). However, like Planck before him, he did this without having a physical justification. Figure 94 De Broglie used his proposed matter waves to explain why Bohr’s atomic orbits would…

Even in the light of the Compton Effect, critics of the early single-photon interference experiments dismissed the importance of the observation by noting that a photon doesn’t have mass. Through some fancy hand-waving, they argued that the low-light interference could be caused through splitting and recombining the light quanta’s wavefront. Decisive proof would come when…

So, yet again, what is the answer? Is light a wave, or is light a stream of particles? Well, actually it’s neither (or both). Light apparently is something different altogether, but it behaves as a wave when the experiment is designed to reveal its wave-like properties, while it behaves as a particle when the experiment is designed to show…

A regular TV camera wouldn’t be able to detect anything at the low-photon flux we need to ensure only one photon passes the slits at a time. An “image-intensifier tube”—like those used by soldiers to see at night—is needed to make the image visible to a conventional camera element (e.g., a CCD camera). In our…

Taylor exposed photographic plates for up to 3 months to obtain interference patterns using his very weak light source. Today, we can conduct the same experiment within a few minutes, using the setup shown in the block diagram of Figure 90. The basic idea remains the same—to illuminate the double slit with a very weak beam.…

So light is a particle, right? But wait! What about diffraction and interference? Didn’t Foucault show that the speed of light in air and water needed to explain diffraction disagree with experimental data if we assume that light is a stream of particles (Figure 7)? And isn’t interference supposed to be the obvious signature of…

cTo observe the Compton Effect we need a source of high-energy photons and a suitable spectrometer to observe the frequency shift in photons as they recoil. The source of short-wavelength photons is not much of a problem—a 137Cs source produces photons at a wavelength λ = 1.88 × 10−12 m. Actually, the more common unit for expressing…

We saw the importance of the concept of quantization as a way of solving a large number of problems with which classical physics had struggled without success. Quantization certainly suggested that light—as Einstein had proposed in 1905—is a stream of particles. However, many physicists refused to take quantization as more than an elegant mathematical trick…