Which experiment is responsible for finding out the charge on an electron?

Options

A. Millikam's oil drop experiment
B. Cathode ray discharge tube experiment
C. Rutherford's `alpha`-rays scattering experiment
D. Photoelectric experiment

Answer

To determine which experiment is responsible for finding out the charge on an electron, we can analyze the key experiments in the history of atomic structure. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Key Experiments
We need to consider the most significant experiments that contributed to our understanding of the electron and its charge. The main experiments to consider are:
- Cathode Ray Tube Experiment
- Millikan's Oil Drop Experiment
- Rutherford's Alpha Scattering Experiment
- Photoelectric Effect Experiment

### Step 2: Analyze Each Experiment
1. **Cathode Ray Tube Experiment**: This experiment, conducted by J.J. Thomson, helped in the discovery of the electron and established that it has a negative charge. However, it did not provide a precise measurement of the charge.

2. **Millikan's Oil Drop Experiment**: This experiment, conducted by Robert Millikan, was specifically designed to measure the charge of the electron. Millikan suspended tiny oil droplets in an electric field and measured how they moved, allowing him to calculate the charge on an electron accurately.

3. **Rutherford's Alpha Scattering Experiment**: This experiment revealed the presence of a dense nucleus in atoms and provided insights into atomic structure but did not measure the charge of the electron.

4. **Photoelectric Effect Experiment**: This experiment demonstrated the emission of electrons from a metal surface when light shines on it. It provided insights into the particle nature of light but did not measure the charge of the electron.

### Step 3: Conclusion
Based on the analysis, the experiment that is responsible for finding out the charge on an electron is **Millikan's Oil Drop Experiment**.

### Final Answer
The correct answer is **Millikan's Oil Drop Experiment** (Option A).

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