An electron of known kinetic energy is directed toward a hydrogen atom initially in its ground state. In different collision events, the incident electron may be deflected without changing the internal state of the atom, may excite the atomic electron to a higher bound state, or may ionise the atom. Which statement correctly distinguishes an elastic atomic collision from an inelastic atomic collision?
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Question

An electron of known kinetic energy is directed toward a hydrogen atom initially in its ground state. In different collision events, the incident electron may be deflected without changing the internal state of the atom, may excite the atomic electron to a higher bound state, or may ionise the atom. Which statement correctly distinguishes an elastic atomic collision from an inelastic atomic collision?

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G1 Physics · Accepted Answer

In an elastic atomic collision, the internal energy of the atom does not change. The projectile and target may exchange translational kinetic energy and momentum, but the atom remains in the same internal quantum state. In an inelastic collision, part of the translational kinetic energy is converted into internal atomic energy. This may produce excitation or ionisation. Therefore excitation and ionisation are inelastic processes, whereas an elastic collision leaves the internal state unchanged.…