Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!brl-tgr!gwyn From: gwyn@brl-tgr.ARPA (Doug Gwyn) Newsgroups: net.sci Subject: Re: Questions on PHOTONS Message-ID: <2997@brl-tgr.ARPA> Date: Thu, 7-Nov-85 20:21:28 EST Article-I.D.: brl-tgr.2997 Posted: Thu Nov 7 20:21:28 1985 Date-Received: Sat, 9-Nov-85 05:24:43 EST References: <1092@mtuxo.UUCP> Organization: Ballistic Research Lab Lines: 60 > What's a photon? A theoretical construct postulated to account for the particle-like aspects of light, specifically the photoelectric effect. Quantum field theorists think in terms of particles as the carriers of interaction; photons then are the particles for the electromagnetic interaction according to this theory. Most of the other questions have to be interpreted in the context of some theory or another; photons are not simple isolatable particles that can be studied in captivity. In particular, photons do not "bounce" off things. They may be absorbed by material particles and other photons emitted at the the same (or a later) time. The energy of the emitted photon could be different from that of the absorbed photon, depending on the state of motion of the material. > If I have a hollow sphere with a mirror coating on the inside > and a light source in it, and say the light cannot get out of the > inside of the sphere, if I leave the light source on for a while, > will the sphere fill up with photons? Will it get full? > Will it get brighter and brighter in there? If I keep the light on > in there for 30 years then suddenly break open the sphere, will > I be blinded by all the light that explodes out of it? Assuming you could prevent absorption of the light by the vessel, eventually an equilibrium would be reached between the field energy and the light source. Since the walls of the vessel will actually be absorbing and emitting radiation also, the system is much like the traditional "black body". If you pump enough energy into it, it will be glowing like a star (or other furnace) inside. The walls would also eventually glow on the outside, in practice. You can be blinded by peering into a furnace without proper eye protection.. > What's the difference between photons in a red light and photons in a > blue light. I thought red and blue light are energy in a certain > wavelength. Does a photon have a wavelength? The "wavelength" associated with a photon is determined by its energy: E = h * nu, where E is the energy, h is Planck's constant, and nu is the frequency. The frequency and wavelength are reciprocally related: lambda * nu = c, where lambda is the wavelength and c is the speed of light. Combine these and you get: E * lambda = h * c. Yes, spectral color is determined by wavelength. Note that a single photon of visible light contains an insignificant amount of energy compared to quantities encountered in daily life.