. The Bell System technical journal . does not involve the mass at all. In the usual loosephrasing, Hp gives the momentum of the particle provided that its chargeis known. The like cannot be said for the energy, which is given byHp only if both the charge and the rest-mass are known. For particlesof the cosmic rays it is best to disregard the ordinary expression forkinetic energy {^mv^) and adopt for good the relativistic expressionmc^, to wit, moc^l^l — v^/c^. Of this the portion wqC^ is not kineticenergy: it is the rest-energy associated with the rest-mass Wo,inseparable from the particle so
. The Bell System technical journal . does not involve the mass at all. In the usual loosephrasing, Hp gives the momentum of the particle provided that its chargeis known. The like cannot be said for the energy, which is given byHp only if both the charge and the rest-mass are known. For particlesof the cosmic rays it is best to disregard the ordinary expression forkinetic energy {^mv^) and adopt for good the relativistic expressionmc^, to wit, moc^l^l — v^/c^. Of this the portion wqC^ is not kineticenergy: it is the rest-energy associated with the rest-mass Wo,inseparable from the particle so long as this exists; it amounts to abouthalf-a-million electron-volts or Mev for the electron, to about1000 Mev for the proton. The remainder may be called kineticenergy. For nearly all of the electrons and most of the other cosmic-ray particles, this remainder is by far the greater part. The de-pendence of the kinetic energy upon Hp is exhibited, for electronsand for protons, by Fig. 13 (page 213). One sees that for different. Fig. 9—Track exhibiting measurable and unequal curvatures on the two sides ofa metal plate, thus indicating changes of energy and momentum suffered in thetraversal. (Anderson) masses a given //p-value leads to dififerent energy-values, but alsothat the error due to an incorrect estimate of rest^mass becomesproportionately smaller as the iJp-value increases. Yet the possi-bility of the error is always there, if the mass of the particle is notcertainly known; and it affects many published energy-values CONTEMPORARY ADVANCES IN PHYSICS 201 based on the presumption—often admitted in the context to be morethan doubtful—that the particles to which they refer are danger might be mitigated by describing these as quasi-energy-values expressed in quasi-Mev.—For actual electrons with mo-menta as great as those figuring in the cosmic rays, the energy-valuein electron-volts is practically equal to 300 times the 7/p-value ex-pressed in gau
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