Quote Everything emits EM waves. Your sofa emits IR radiation. The displays, since they generate light, emit EM in the visible spectrum, as well as IR radiation. A wall will block both types of radiation, visible and IR. QuoteCan you or some one here elaborate ? I'm trying to understand this and having problems understanding this.
All matter (with the exception of very low density gas) will emit electromagnetic radiation. The particular type of radiation is determined by the object's temperature. Your sofa, because it is not particularly hot, emits infra-red (IR) radiation. You sitting on the sofa also emit IR radiation, although of a slightly different type, since you are warmer than a sofa. This, incidentally, is the basis for some types of night vision equipment. A hotter object will emit visible light, which is why a nail glows if you hold over a fire. A wall will block IR and visible radiation, which you can verify by standing and looking at the one by your kitchen, and noting that you cannot see through it, nor feel the heat from a stove on the other side.
This phenomenon is called the Blackbody Radiation (see source for technical details) It basically states that all objects have heat (which is all objects) can generate EM radiation. A simple example is that the hot iron has a red glow, because that's primarily the frequency of the EM radiation that it emitts. However a cold iron bar emits EM radiation as well, except that it's very weak in intensity and has the wrong frequency that human eyes can't detect it Again, all objects emit EM radiation...you sofa, your radiator and yourself As it turns out, most objects in normally day life emit IR radiation. This is the principle of thermo-camera, which takes the IR radiation, and calculates the temperature of the object
The key word is EVERYTHING emits EM waves. That means literally everything. The walls, floor, ceiling, and everything else in your room (including you) are also emitting IR radiation. If they are all at the same temperature as your sofa, then the sofa is receiving as much radiation from everything else in the room as it is emitting. That is why it stays at the same temperature, and all this radiation doesn't contradict the principle of conservation of energy. The amount of EM radiation that is omitted and its wavelength depends on the temperature of the object. Hot objects emit more radiation at shorter wavelengths. If you switch on an electric hotplate, first you can feel the heat (IR radiation) coming from it. When it gets hotter it emits shorter wavelengths and eventually is starts to emit visible red light. The filament of a light bulb gets even hotter and emits the whole spectrum of visible light, which is why it appears (approximately) white. If also emits a lot of IR radiation as heat. Everything that is at a temperature above absolute zero (0 degrees Kelvin or -273 Celsius) emits EM waves. One of the best pieces of evidence for the big bang is that it is still possible to detect the EM radiation from the original explosion traveling through space, though it has now cooled down to a temperature of about 2 degrees K.
Yes, even very cold things. The colder the object, the longer the wavelengths it emits and also the less it emits. But everything emits. You may or may not have heard about the cosmic microwave background. This is electromagnetic radiation that is seen everywhere in the blank parts of the sky. It has the electromagnetic spectrum of an object which is at 2.7 K, that is 2.7 degrees above absolute zero. Much, much colder than the north pole. So in a very real sense the universe has a temperature of 2.7 degrees. This program is studying that background in detail for clues about the early universe. map.gsfc.nasa /
Re the last part, the amount (and frequency) of the IR radiation is proportional to the ABSOLUTE temperature, which is about –273?C At absolute zero, there is no radiation emitted. North pole is a long way from absolute zero, so it emits radiation. Matter in space, in the light of the sun, is quite hot. Matter far from the sun or in the shade is a lot colder, but not quite down to absolute zero. wikipedia: All of the observable Universe is filled with photons that were created during the Big Bang, which is known as the cosmic microwave background radiation (CMB). There is quite likely a correspondingly large number of neutrinos called the cosmic neutrino background. The current black body temperature of this photon radiation is about 3 K (?270 °C; ?454 °F). Some regions of outer space can contain highly energetic particles that have a much higher temperature than the CMB. .
