Question

In which of the following, emission of electrons does not take place

• A. thermionic emission
• B. X-rays emission
• C. photoelectric emission
• D. secondary emission

Answer 1

The Correct Option is B

In order to determine in which of the given options the emission of electrons does not take place, we need to understand the processes involved in each emission type:

1. Thermionic Emission: This is the process where electrons are emitted from a material upon heating. The thermal energy provided to a material causes electrons to gain enough energy to overcome the binding forces holding them within the material.
2. Photoelectric Emission: In this process, electrons are emitted from a material when it is exposed to light (usually ultraviolet light). The energy from the light photons is absorbed by the electrons, allowing them to escape the material's surface.
3. Secondary Emission: This occurs when a primary electron (or another particle) strikes a material, causing the ejection of one or more secondary electrons.
4. X-rays Emission: This is the process where X-rays are produced, typically when high-speed electrons strike a metal target in an X-ray tube, or naturally, in astronomical events. In this process, electrons do not get emitted; instead, the interaction leads to the emission of X-rays, a type of electromagnetic radiation.

From this analysis, it is clear that the emission of electrons is a characteristic of thermionic, photoelectric, and secondary emissions. However, in X-rays emission, what is emitted are X-ray photons, not electrons.

Hence, the emission of electrons does not take place in X-rays emission, making it the correct answer.