Author: Haroon Khalil
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IMAGING SINGLE PHOTONS
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…
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TWO-SLIT INTERFERENCE WITH SINGLE PHOTONS
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.…
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WHAT IS THE NATURE OF LIGHT?
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…
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GAMMA-RAY SPECTRUM ANALYSIS
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…
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Introduction
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…
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QUANTIZATION-THE CORE OF QUANTUM PHYSICS
Let’s quickly review the major problems faced by classical physics at the turn of the twentieth century: 1. Classical physics would predict that a blackbody should radiate an infinite amount of UV light. However, hot objects actually produce a limited glow that peaks at a wavelength dependent on temperature and then decays to zero at short…
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ORBITALS AND NOT ORBITS
In spite of its success with explaining the spectral lines produced by the hydrogen atom, Bohr’s atomic model is not perfect. It only works for atoms that have one electron. That is, it only applies to hydrogen, ionized helium (He+), doubly ionized lithium (Li++), and a few other light ions. More importantly, however, it does…
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BOHR’S SPARK OF GENIUS
Rydberg had been able to capture the observed periodicity of the hydrogen lines in an elegant formula, but he had no idea what underlying physical process could be responsible for such mathematical regularity. Returning to 1911, we find the world of physics was faced with a major riddle about the atomic structure proposed by Rutherford.…
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EMISSION SPECTROSCOPY
Let’s see those hydrogen lines for ourselves! We will use the kind of hydrogen “spectrum tube” available at any store that sells educational scientific supplies. Although they are all pretty much the same, their price varies quite a bit based on the store’s brand name. The least-expensive spectrum tubes are sold by Information Unlimited (under…
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Introduction
In this app last section left us with a planetary model of the atom that takes into account the existence of the nucleus, but which is inherently unstable. To recap, the model proposes that the centrifugal force of the revolving electron just exactly balances the attractive force of the nucleus. However, the issue is that…