# Class 12 Physics MCQ – Electron Emission

This set of Class 12 Physics Chapter 11 Multiple Choice Questions & Answers (MCQs) focuses on “Electron Emission”.

1. Identify the process in which an electron escapes from the metal surface.
a) Electron emission
b) Electron displacement
c) Electron transgression
d) Electron movement

Explanation: The process in which an electron escapes from the metal surface is known as electron emission. Electrons are loosely bound to the nucleus, and therefore, a little energy push sets these electrons flying out of their respective orbits.

2. How many types of electron emissions exist?
a) 2
b) 3
c) 4
d) 1

Explanation: There are four types of electron emissions, namely, thermionic emission, photoelectric emission, secondary emission, and field emission. These are the different methods of producing electron emissions.

3. Which of the following are quick electron emissions?
a) Photoelectric emission
b) Field emission
c) Secondary emission
d) Thermionic emission

Explanation: Field electron emission, or simply field emission, is known as quick electron emissions because, in this type of electron emission, the emission of electrons is induced due to the presence of an electrostatic field.

4. Thermionic emission is dependent on temperature.
a) True
b) False

Explanation: Yes, this is a true statement. Thermionic emission is the process of electron emission involving the liberation of electrons from an electrode by virtue of its temperature and this is done by releasing the energy supplied by heat. This happens as the thermal energy given to the charge carrier overcomes the work function of the material.

5. Find the wrong statement.
a) An electron gun is to create electrons and then accelerate them to a very high speed
b) Thermionic emissions and photoelectric emissions are the same
c) The kinetic energy of photoelectrons vary
d) Vacuum tubes are thermionic devices

Explanation: No, thermionic emissions and photoelectric emissions are not the same. During thermionic emissions, the electrons are emitted from the metal surface by providing heat energy, whereas, during photoelectric emission light energy is emitted when electrons are emitted from the surface of the metal. So, it is the opposite in operation.
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Sanfoundry Global Education & Learning Series – Physics – Class 12.

To practice all chapters and topics of class 12 Physics, here is complete set of 1000+ Multiple Choice Questions and Answers.