Physical chemistry is the part of chemistry that seeks to account for the properties and transformations of matter in terms of concepts, principles, and laws drawn from physics. This glossary is a compilation of definitions, descriptions, formulae, and illustrations of concepts that are encountered throughout the subject. This section describes the concepts that begin with the letter Y; where appropriate, the entries also describe subsidiary but related concepts. Refer to the Directory for a full list of all the concepts treated.
Young’s Modulus
Young’s Slits
In the Young’s slits experiment, a diffraction pattern is observed on a screen placed behind an opaque screen with two parallel slits a short distance apart and illuminated with monochromatic light (Figure Y.1). A diffraction pattern is also seen if the light is replaced by a monochromatic stream of electrons, so confirming their wavelike character. The pattern is observed even when the intensity of the beam is reduced to the point that only one electron at a time passes through the slits, suggesting that the electron senses the presence of a second slit even though it is passing through another slit. This paradox, which arises from improperly mixing position and momentum descriptions, is resolved by expressing the entire apparatus, including the screen with its slits, in a wave (linear momentum) formalism and invoking the conservation of linear momentum in the interaction of the wavelike electrons and the wavelike recreation of the screen with its slits.
Diffraction by two slits.
