Photoelectric emission from a given surface of metal can take place when the value of a ‘physical quantity’ is less than the energy of incident photon. The physical quantity is :

Options

A. Threshold frequency
B. Work function of surface
C. Threshold wave length
D. Stopping Potential

Answer

To solve the question regarding the physical quantity related to photoelectric emission from a metal surface, we need to analyze the options provided and understand the concept of photoelectric effect.

### Step-by-Step Solution:

1. **Understanding Photoelectric Emission**:
- Photoelectric emission occurs when photons strike a metal surface and eject electrons from it. For this to happen, the energy of the incident photons must be sufficient to overcome the energy barrier that holds the electrons in the metal.

2. **Energy of Incident Photon**:
- The energy \( E \) of a photon is given by the equation:
\[ E = h \nu \]
where \( h \) is Planck's constant and \( \nu \) is the frequency of the photon.

3. **Threshold Frequency**:
- The threshold frequency \( \nu_0 \) is the minimum frequency required for photoelectric emission to occur. The energy corresponding to this frequency is:
\[ E_0 = h \nu_0 \]
- If the frequency of the incident photon is less than the threshold frequency, no photoelectric emission will occur.

4. **Work Function**:
- The work function \( \phi \) (or \( W \)) of a material is defined as the minimum energy required to remove an electron from the surface of the metal. It is related to the threshold frequency by:
\[ \phi = h \nu_0 \]
- For photoelectric emission to occur, the energy of the incident photon must be greater than the work function:
\[ E > \phi \]

5. **Conclusion**:
- The physical quantity that must be less than the energy of the incident photon for photoelectric emission to occur is the **Work Function** of the surface. Therefore, the correct answer to the question is:
\[ \text{Work Function of Surface} \]