The phenomenon which suggested that light emitted in packets (quanta) is

Options

A. electron diffraction
B. photoelectric effect
C. diffraction of light
D. black body radiation.

Answer

To solve the question regarding the phenomenon that suggests light is emitted in packets (quanta), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Light as Quanta**:
- Light can be thought of as being made up of discrete packets of energy called "quanta" or "photons." This concept was introduced by Max Planck and later expanded by Albert Einstein.

2. **Identify the Relevant Phenomenon**:
- Among the options provided (electron diffraction, photoelectric effect, diffraction of light, black body radiation), we need to identify which phenomenon is directly related to the emission of light in packets.

3. **Define the Photoelectric Effect**:
- The photoelectric effect occurs when light (or electromagnetic radiation) strikes a metal surface and causes the emission of electrons. This phenomenon demonstrates that light can behave as particles (photons) with quantized energy.

4. **Mathematical Expression**:
- The energy of the emitted electrons can be expressed mathematically as:
\[ E = \frac{hc}{\lambda} = \text{Work Function} + \text{Kinetic Energy} \]
- Here, \(E\) is the energy of the photon, \(h\) is Planck's constant, \(c\) is the speed of light, and \(\lambda\) is the wavelength of the light.

5. **Conclusion**:
- Based on the definition and the mathematical formulation, the phenomenon that suggests light is emitted in packets (quanta) is the **photoelectric effect**.

### Final Answer:
The phenomenon which suggested that light emitted in packets (quanta) is the **photoelectric effect**.