![]() It disappears, from all over space, never to be seen again! Somehow, those parts of the wave distant from the point of interaction know that the energy has been lost and disappear, instantaneously. If the electron or photon propagates as a wave but deposits its energy at a point, what happens to the rest of the wave? So while the electron propagates through space like a wave, it interacts at a point like a particle. The energy of the electron is deposited at a point, just as if it was a particle. ![]() The bizarre thing about the diffraction experiment is the electron wave doesn’t deposit energy over the entire surface of the detector, as you might expect with a wave crashing on the shore. These notions form the basis of quantum theory, perhaps the most successful theory scientists have ever developed. ![]() This is another example of the Young’s slit experiment we showed above, but this time using electron waves. When we fire electrons at one side of a screen with two closely spaced holes and measure the distribution of electrons on the other side, we don’t see two peaks, one for each hole, but a complete diffraction pattern, just as if we had been using waves. Electron and atom diffractionĮxperiments proved atomic particles act just like waves. If this is true, a particle should diffract through a pair of closely spaced holes, just like a wave. To explain the structure and behaviour of atoms it was thought necessary to assume that particles have wave-like properties. If light, that we thought was wave-like, also behaves like a particle, could it be that objects such as electrons and atoms, that are particle-like, can behave like waves? So the notion came about that light waves act like particles - these particles are called photons. The answer was to assume the energy of light waves was not continuous but came in fixed amounts, as if it was composed of a large number of particles, like our handful of marbles. These theories would always predict infinite energy for the light emitted beyond the blue end of the spectrum - the ultraviolet catastrophe. This light is called black-body radiation. But at the beginning of the 20 th century, a problem was found with the theories of light waves emitted from hot objects, such as hot coals in a fire or light from the sun.īlackbody radiation from hot coals in a fire. The phenomenon of diffraction is a well-known property of light waves. On the other side of the screen, the marble will be found travelling in one of two directions, depending on which hole it went through. In contrast, a marble thrown at the screen either bounces off or goes straight through one of the holes. The image on the left shows an example of the double slit experiment invented by English polymath Thomas Young. The waves spread out in all directions and interfere, leading to regions in space where the wave disappears and regions where it becomes stronger. This can be seen when parts of a wave pass through closely spaced holes in a screen. ![]() The waves above the screen show regions of destructive interference, where the wave crests overlap troughs and cancel out, and regions of constructive interference, where the wave crests overlap crests and reinforce. The holes can be seen near the bottom of the image. The interference pattern of a wave incident on a two holes in a screen.
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