Define the following: Threshold frequency and work function.

Hint The above problem is based on the concept of the photoelectric effect. The photoelectric effect is the phenomenon in which the movement of the charge carries due incident light. This phenomenon depends on the frequency or wavelength of the incident light and nature of the metal surface.

Complete step by step answer
When the light of adequate frequency falls on the metal surface then the electrons are emitted from the metal surface. The emission of the electrons occurs due to the energy of the photons of incident light. The minimum frequency of the incident light at which the emission of the electrons starts is called the threshold frequency. It is different for different materials.
The minimum energy necessary to initiate the photoelectric effect from the metal surface is called the work function. It depends on the nature of the metal surface and a property of the metal.
The expression for the threshold frequency and work function is given by the following formula,
${f_0} = \dfrac{W}{h}$
Here, W is the work function of the material and h is the Planck’s constant.

Additional Information The emission of the electrons can also occur by Thermionic emission, Field emission or bombarding of the high speed electrons or nuclear particles. The electrons emitted in the photoelectric effect are also called the photoelectrons.

Note The photoelectric effect only occurs if the energy of the incident light is greater than the work function of the material and frequency of the incident light is greater than the threshold frequency of the metal.