classical physics
...x Planck introduced the quantum theory. In his theory, energy is not a continuous quantity, but is discretely packed in bundles called quanta. There are everyday phenomena that are quantized. Some examples are shoe size, shirt size, money, “age”. Quantized energy was calculated with the equation: E = h c/l E = h f (h = 6.63 x 10-34 J s) In 1905, Albert Einstein applied Planck’s quantum theory and explained successfully the photoelectric effect. According to the new theory, only light from certain frequencies have the minimum energy required for the photoelectric effect to occur (photons). The fact that light was made of photons created a serious problem in physics because light was thought to be a wave. There is evidence that light behaves as particles called photons AND that light behaves as a wave. As a consequence, light has a dual nature: it can be described as a wave AND as a particle, depending on the type of experiment. Bohr model of the atom Contrary to the dispersion of light (you get a continuous color spectrum), when an element is heated enough it emits a line emission spectrum of specific frequencies and wavelengths. Each element produces its own sets of color lines. Also, when visible light passes through a sample of a cool gaseous element before entering the spectrometer (apparatus used to measure spectrum lines), a line absorption spectrum is created. The absorption spectrum is continuous except for some specific color lines that are missing. The line EMISSION spectrum and the line ABSORPTION spectrum are a “negative image” of each other. The color lines that are missing on the line absorption spectrum are the same (and at the same distance) in the line emission spectrum. Niels Bohr reasoned that a discrete line spectrum must be the result of a quantum effect. As a consequence, Bohr hypothesized that in the hydrogen atoms (and some other simple atoms), electrons must be in discrete or specific orbits with particular radii that could be describe with a set of quantum numbers. Bohr also proposed that when electrons jump from the “ground state” (orbit of lowest energy) to an “excited state” (orbits of higher energy) they absorbed energy, creating the line ABSORPTION spectrum, and that when electrons move from an “excited state” to the “ground state” they release energy, creating the line EMISSION spectrum. The allowed electron orbits depend on the principal quantum number. For ground state, n = 1. For electrons to jump to a specific excited orbit, they require the energy carried by a photon of specific frequency and wavelength (n > 1). The radius of a particular orbit is given by: rn = (0.053 nm) (n2) The total energy of an electron in an allowed orbit is given by: En = (-13.60 eV) (1/n2) Electrons might jump from one orbit to the next or jump to nonconsecutive orbits, depending on how much energy (photons) are received or emitted. The transition series indicate the energy (photons) that is emitted or received when electrons jump orbits. These series depend only on the principal quantum number. There are five series: Lyman lines: An electron starts from n = 1 and jumps to a higher level or an electron drops from a higher level to n = 1. Balmer lines: An electron starts from n = 2 and jumps to a higher level or an electron drops from a higher level to n = 2. Paschen lines: An electron starts from n = 3 and jumps to a higher level or an electron drops from a higher level to n = 3. Brackett lines: An electron starts from n = 4 and jumps to a higher level or an electron drops from a higher level to n = 4. Pfund line: An electron starts from n = 5 and jumps to a higher level or an electron drops from a higher level to n = 5. The Lyman lines fall in the ultraviolet portion of the spectrum. The Balmer lines fall in the visible portion of the spectrum. The Paschen, Brackett, and Pfund lines fall in the infrared portion of the spectrum. Microwave oven A microwave oven uses microwaves to heat food. Microwaves are electromagnetic waves. In the case of microwave ovens, the commonly used wave frequency is roughly 2,500 megahertz (2.5 gigahertz). Waves in this frequency range have an interesti...