![]() This is due to destructive interference in those regions, a phenomenon characteristic of waves. Observing the regions where the probability is minimum with both slits open, we notice that the number of counts with both slits open is smaller than the counts with only one slit open. This pattern looks like the interference fringes obtained in the original Young’s double-slit experiment with waves shown in Figure 18.9! Figure 22.3 is a photograph of the interference pattern for electrons in a double-slit experiment. Uncovering both slits gives us the pattern shown in Figure 22.2c for the probability of arrival. If we cover either one of the slits and let the experiment run for some time, counting the number of flashes at any given position on the screen, what we obtain for the probability of arrival of the electron at various locations on the screen is the pattern shown in Figure 22.2b. What we observe is that the flashes on the screen indicate that each electron hits the screen in just one point. Can we think of light as made up of particles and still understand Young’s double-slit experiment? What if we use electrons instead of photons?Ĭonsider a source of electrons, like the electron gun in a regular television tube, a thin metal plate with two very narrow slits in it, and a phosphor-coated screen that produces a flash when an electron collides with it, like a television screen (Figure 22.2a). Light, Einstein told us, also behaves as a particle. In fact, this was the experimental proof given by Young that light was a wave phenomenon. We can understand this interference pattern if we think of light as a wave. These beams interfered with each other, producing an interference pattern on a screen. In Chapter 18, we discussed the diffraction of light in Young’s double-slit experiment in which a beam of light passed initially through a single narrow slit and then through a pair of slits that formed two coherent beams. To illustrate this principle, let’s consider a possible experiment with electrons. This statement is known as Heisenberg's uncertainty principle. ![]() In 1927, Heisenberg showed that if two matrices q and p represented two physical properties of a particle, like position and momentum or time and energy, which obeyed the noncom mutative rule, that is, that the difference between the products pq and qp was proportional to Planck’s constant, then one could not measure both properties simultaneously with infinite precision. In Helgoland, we recall, Heisenberg had discovered that observable or measurable quantities were to be represented by matrices.
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