Question

Which of the following when falls on a metal will emit photoelectrons?
A. UV radiations
B. Infrared radiations
C. Radio waves
D. Microwaves

Answer 1

To solve this question, we should have a concept about the photoelectric effect and we know that when light or any other radiation of the proper frequency falls on a metal's surface, the photoelectric effect occurs, resulting in the emission of electrons from the metal's surface. The number of emitted electrons is proportional to the frequency of light, and the number of emitted electrons is proportional to the intensity of light.

Complete step by step answer:
When light interacts with matter, it behaves as if it were made up of discrete packets of energy, according to the photoelectric effect. Quanta are the units of energy that make up these packets. The energy of each quantum of light is $h\nu$ , where $h$ is Planck's constant and $\nu$ is the light's frequency.

So, we can easily say that the radiations or waves which have more frequency will easily emit the photoelectrons when falling on a metal, and we know that UV radiations have the most frequency other than all above options so, we can say that, option A is the correct option.

Hence, option A is the correct answer.

Note: Electric and magnetic forces do not deflect photons since they are electrically neutral particles. In addition, regardless of the intensity of radiation, all photons of a specific frequency and wavelength will have the same energy and momentum. Photoelectrons can be emitted in any direction with any velocity between zero and the maximum velocity that an electron can acquire during photoelectric emission from a metal surface.