Photons apparent mass

Note that the apparent mass of a photon depends on its wavelength. A photon does not have mass in a classical sense. 

Using this form of the eqnation, we can calculate the mass associated with a given quantity of energy. For example, we can calculate the apparent mass of a photon For electromagnetic radiation of wavelength A, the energy of each photon is given by the expression... 

Then the apparent mass of a photon of light with wavelength A is given by... 

X rays and electrons that showed that photons do exhibit the apparent mass calculated from the preceding equation. However, it is clear that photons do not have mass in the classical sense. A photon has mass only in a relativistic sense—it has no rest mass. 

Neutrinos and light quanta (photons) apparently possess momentum but not rest mass, and thus... 

Figure 7. Time-resolved mass spectrometry. AU-trcms-(2, 4, 6, 8) decatetraene was excited to its 5 2 electronic origin with a femtosecond pulse at A-pump — 287 nm. The excited-state evolution was probed via single-photon ionization using a femtosecond pulse at ApIObe = 235 nm. The time resolution in these experiments was 290 fs (0.3 ps). The parent ion CioH signal rises with the pump laser, but then seems to stay almost constant with time. The modest decay observed can be fit with a single exponential time constant of 1 ps. Note that this result is in apparent disagreement with the same experiment performed at Xprobe — 352 nm, which yields a lifetime of 0.4 ps for the S2 state. The disagreement between these two results can be only reconciled by analyzing the time-resolved photoelectron spectrum.

An ideal interface should not cause extra-column peak broadening. Historical interfaces include the moving belt and the thermospray. Common interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Several special interfaces include the particle beam—a pioneering technique that is still used because it is the only one that can provide electron ionization mass spectra. Others are continuous fiow fast atom bombardment (CF-FAB), atmospheric pressure photon ionization (APPI), and matrix-assisted laser desorption ionization (M ALDl). The two most common interfaces, ESI and APCI, were discovered in the late 1980s and involve an atmospheric pressure ionization (API) step. Both are soft ionization techniques that cause little or no fragmentation hence a fingerprint for qualitative identification is usually not apparent. 

Indeed, considering that photons are rather peculiar particles in that they have zero rest mass and can exist only when travelhng at the speed of fight, it seems reasonable that the wave associated with the motion of any particle should become more and more apparent as the mass decreases, rather than the wave coming into existence suddenly when the rest mass vanishes. 

Although both photons and electrons show an apparent duality, they are not the same kinds of entities. Photons always travel at speed c and have zero rest mass electrons always have v < c and a nonzero rest mass. Photons must always be treated relativistically, but electrons whose speed is much less than c can be treated nonrela-tivistically. 

Much of solid-state physics is carried out in reciprocal space, sometimes called Fourier space. The reasons for this will become more apparent as we progress. One of the more obvious reasons is that it is easier to represent the momentum of photons and phonons as well as particles such as electrons and neutrons and thus their interactions in reciprocal space. Recall that the momentum of either a massless particle such as a photon or a particle with mass can be written as... 

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