b. The energy of each photon is directly proportional to the frequency of the light.

c. The interaction between a photon and an electron in the metal is a unique, elemental act, in which the photon can give up some, or all of its energy to the electron, which then might have enough energy to escape from the metal.

The electron is kept in the metal by the electric forces, and can only escape if a certain minimum amount of energy is given to it. If the photon energy (i.e. frequency) is too low to overcome this attractive force between the electrons and the metal, the electron can't escape. Thus the frequency of the photon must be above a certain value (which depends on the particular metal). Once we are above this threshold, the photon either hits an electron or it doesn't. If it does, and if enough energy is transferred to the the electron from the photon, the electron will have enough energy to escape IMMEDIATELY, with no time delay. Also, if we increase the energy of the photon by increasing its frequency, the electrons which interact with these electrons can come off with increased energy).

Einstein's conjecture that the energy of a photon is proportional to its frequency can be written E_photon = h f ; here h is Planck's constant.

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