The splitting of line into groups under the effect of magnetic field is called

Options

A. (a) Stark effect
B. (b) Zeeman effect
C. (c) photoelectric effect
D. (d) screening effect

Answer

To solve the question regarding the splitting of spectral lines into groups under the effect of a magnetic field, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks about the phenomenon where spectral lines split into groups when subjected to a magnetic field.

2. **Identify the Options**: The options provided are:
- Stark effect
- Zeeman effect
- Photoelectric effect
- Screening effect

3. **Analyze Each Option**:
- **Stark Effect**: This effect refers to the splitting and shifting of spectral lines due to an external electric field, not a magnetic field. Therefore, this option is incorrect.
- **Photoelectric Effect**: This phenomenon occurs when light (electromagnetic radiation) strikes a surface and causes the emission of electrons. It is unrelated to the splitting of spectral lines, so this option is also incorrect.
- **Screening Effect**: This effect describes the reduction of the effective nuclear charge on an electron due to the presence of other electrons. It does not pertain to the splitting of spectral lines under a magnetic field, making this option incorrect as well.
- **Zeeman Effect**: This effect, named after the Dutch physicist Pieter Zeeman, describes the splitting of spectral lines into multiple components when subjected to a magnetic field. This is the correct option.

4. **Conclusion**: Based on the analysis, the correct answer to the question is the **Zeeman effect**.

### Final Answer:
The splitting of lines into groups under the effect of a magnetic field is called the **Zeeman effect**.

---