Does a microwave frequency change when it bounces off a target

Question

and if it does change then does it change differntly depending on the material

ex. cloth changes by 1 , brick changes by 3 ??????????

i think it would because differnt materials have differnt absorption of a radiation and that might change the frequency or would it just change the intensity of the reflected beam

Answer 1

yes, any radiation bouncing off materials changes frequency and hence wavelength due to absorption rates. but the bandwidth of certain electromagnetic radiations is sufficiently big that if a microwave bounces off a surface, its very likely that it will still be a microwave but with very slightly different frequency

Answer 2

Both the above answers are right and both are wrong.  Vincent has the better answer.

MICROWAVE energy indeed reflects back to the source at a different frequency only when the reflector object is moving towards or away from the source.  That is the Doppler effect.

ENERGY however when absorbed by a target does change frequency and becomes frequently heat whose frequency lies in the infrared range, and can radiate back: if the target becomes white hot then energy could radiate back as light from the target.

The difficulty is that the question is poorly defined.  "Bounces off" is imprecise and can involve either reflection (zero change in frequency unless the target is moving) or absorption and re-radiation.

Answer 3

There are lots of strange quantum effects that can govern the behavior of light.

It could change, but more often than not it'll be the same frequency.

Fundamentally, a single photon gives up its energy to an electron bound to a single atom.  That electron can only exist in defined energy states.  The energy levels are not continuous, but are discrete.  They are said to be quantized.

IF the electron can exist in that state, it absorbs the energy is and "jumps" to the new energy state (it's said that it is in a new "orbit").

The electron isn't at rest and eventually some time later it will revert to a lower energy state (not necessarily it's original ground rest state though).  It gives back some or all of the energy from the original photon.  If it stops at an intermediate energy state, the new photon emitted will have a lower amount of energy and will be a lower frequency.  At some time later the rest of the energy will be given up to photon emission.

Check here for a cool University of Oregon flash animation of the process:

http://zebu.uoregon.edu/nsf/emit.html

By the way, the direction in which the new photon is emitted can be any direction whatsoever.  The angle of incidence of a beam of light off of a mirror is equal to the angle of reflection, but that's only true on a very large scale.  It's absolutely not true for a single photon.  Quantum mechanics deals with probabilities and the most probable angle agrees with our observations but not on the very small scale.

Also, another weird thing is that depending on the material and crystal lattice the incident photons interact with, some of the energy can be transferred to mechanical vibration of the crystal lattice.  The leftover energy is available for photon emission and photons associated with those kinds of energy levels are having a different energy (and therefore different frequency) than the incident photon.

Answer 4

It can generally only do that if the object is moving. Then, it's by Doppler shift.

Answer 5

Frequency would change only if the object moves (that is the Doppler effect and is actually used to assess the speed of the object; that is how police speed radar work).

Different materials will return waves with varying intensity, or depending of how deep some portion penetrates before bouncing back (i.e. the signal is returned in a spread out fashion).