速問彈性碰撞與非彈性碰撞

2011-04-16 1:58 am

當熱電子打落gas atom到
如果佢唔夠KE激發gas molecule既電子
佢就lose唔到KE比gas molecule既電子
呢個就係elastic collision

但係
當一粒有足夠大KE既熱電子打落gas molecule到
佢會lose左一部分KE比gas molecule既電子
呢個撞擊既process就會係inelastic collision
即係total KE of 兩粒電子係唔conserved
何解?
乜個粒excited electron gain左既KE唔能夠等於lose左既KE咩?

另外
當一粒光子(hf=excitation energy, ground state to the first excited state)撞到一粒gas molecule既電子
光子既所有能量會用左黎激發個粒電子
又係inelastic collision
點解?
仲有其實粒photon既KE係咩?點計?

Thanks for answering my questions.

回答 (1)

天同

2011-04-16 8:37 am

✔ 最佳答案

Q: 即係total KE of 兩粒電子係唔conserved,何解?
乜個粒excited electron gain左既KE唔能夠等於lose左既KE咩?

The excited electron is not necessarily a free electron. It is still bound to the atom/ Even if an orbital electron becomes free after excitation, energy is needed by the electron to do work against the attractive force of the atomic nucleus. Thus the KE of the electron would be smaller than the energy gained from the bombarding electron. Kinetic energy is not conserved.

Q: 光子既所有能量會用左黎激發個粒電子, 又係inelastic collision
點解?

I think the classical theory of particle collision cannot be applied here, as a photon is itself a packet of energy. You could not regard it as a real particle that has mass.

Q: 仲有其實粒photon既KE係咩?點計?

The term "kinetic energy" is rearely applied to photons. A photon has no rest mass. It is common to say that a photon possesses "energy" and "momentum".

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