Given below is the graph between frequency (v) of the incident light and maximum kinetic energy `(E_k)` of emitted photoelectrons. Find the values of threshold frequency.

The photoelectronic cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy of photoelectrons emitted ?

To emit a free electron from a metal surface a minimum amount of energy must be supplied.When light of frequency 7.21 * 10^14 Hz is incident on a metal surface, the maximum speed of the ejected electrons is 6 x 10^5 m/s . Calculate the threshold frequency for the metal.