Quantum Physics

890 Chapter 27 Quantum PhysicsElectron gunCathodeVacuumAnodeElectromagneticlensElectromagneticcondenserlensCoreCoilElectronbeamSpecimengoeshereSpecimenchamberdoorScreenVisualtransmission(a)ProjectorlensPhotochamberFigure 27.17 (a) Diagram of a transmission electron microscope for viewing a thin sectioned sample.The “lenses” that control the electron beam are magnetic deflection coils. (b) An electron microscope.(b)© David Parker/Photo Researchers, Inc.The electron beam in an electron microscope is controlled by electrostatic ormagnetic deflection, which acts on the electrons to focus the beam to an image.Rather than examining the image through an eyepiece as in an optical microscope,the viewer looks at an image formed on a fluorescent screen. (The viewing screenmust be fluorescent because otherwise the image produced wouldn’t be visible.)Applying Physics 27.3X-Ray Microscopes?Electron microscopes (Fig. 27.17) take advantageof the wave nature of particles. Electrons are acceleratedto high speeds, giving them a short de Brogliewavelength. Imagine an electron microscope usingelectrons with a de Broglie wavelength of 0.2 nm.Why don’t we design a microscope using 0.2-nmphotons to do the same thing?Explanation Because electrons are charged particles,they interact electrically with the sample in the microscopeand scatter according to the shape and densityof various portions of the sample, providing a meansof viewing the sample. Photons of wavelength 0.2 nmare uncharged and in the x-ray region of the spectrum.They tend to simply pass through the thin samplewithout interacting.27.7 THE WAVE FUNCTIONDe Broglie’s revolutionary idea that particles should have a wave nature soonmoved out of the realm of skepticism to the point where it was viewed as a necessaryconcept in understanding the subatomic world. In 1926, the Austrian–Germanphysicist Erwin Schrödinger proposed a wave equation that described how matter