Final answer:
To find the velocity of an electron emitted by a metal, one must use the photoelectric effect equations to first calculate the kinetic energy of the electron using the photon's energy and then use this kinetic energy to find the velocity.
Step-by-step explanation:
The question poses a problem related to the energy of photoelectrons ejected by photons and subsequently measuring the velocity of an electron. The formula that relates the energy of a photon to its frequency is E = hν, where E is the energy of the photon, h is Planck's constant, and ν is the frequency of the photon. The threshold frequency is the minimum frequency needed for electrons to be emitted from the metal. The electron's kinetic energy can be calculated using the excess energy beyond the threshold, using the formula K.E. = E - W, where W is the work function (related to the binding energy) of the metal. Then, using the kinetic energy, the velocity of the electron can be calculated with the relation K.E. = ½mv², where m is the mass of the electron and v is its velocity.