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    I am creating a summary for AS physics however, there is something Im not sure on.

    I know that when a photon collides/ is absorbed by and electron it must have the exact energy that is required for it to move up any energy level but why is this? and what happens if the photon doesnt have enough energy to excite the electron up a distinct energy level?

    I think this is correct: if it doesn’t have the exact energy to move up an energy level, then simply nothing will happen.
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    (Original post by Ladkus)
    Why is this? What happens if photon doesnt have req energy to excite?
    (Original post by JacobPowell)
    nothing will happen
    A characteristic property of each element is energy level config, likewise electron config. If the incident photon doesn't excite an electron(s), with all energy transferred by absorption, atom scatters it.

    In scattering, photons induce electric dipoles; then emitted as dipole radiation in some direction. With small atoms, Rayleigh scattering occurs (elastic); scattering intensity ∝ (1 + cos^[email protected])/(x^2 λ^4).

    Larger particles (smoke, droplets) can Mie scatter, λs scatter equally. Rayleigh is why the sky is blue, sunsets are red and Mars is opposite. Mie is why clouds and horizon's daytime sky are white.

    Photons ejecting electrons from atoms, or collide with free electrons; compton scattered (inelastic). Photons where only some energy is used to excite, scatter at lesser E & f; Raman scattered (inelastic).
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