Who established that electric charge is quantised ?

Options

A. J.J. Thomson
B. William Crookes
C. R.A Millikan
D. Wilhelm Rontgen

Explanation

**Step-by-Step Solution:**

1. **Understanding Quantization**: The concept of quantization refers to the idea that certain properties, such as electric charge, can only take on discrete values rather than a continuous range. This means that electric charge exists in fixed amounts.

2. **Defining Elementary Charge**: The smallest unit of electric charge is known as the elementary charge, denoted as 'e'. The value of the elementary charge is approximately \(1.6 \times 10^{-19}\) coulombs.

3. **Expression of Charge**: Any electric charge (Q) can be expressed as an integral multiple of the elementary charge. This can be mathematically represented as:
\[ Q = n \cdot e \]
where \(n\) is an integer (0, 1, 2, ...), indicating that charge can only exist in whole number multiples of the elementary charge.

4. **Contribution of R.A. Millikan**: The quantization of electric charge was established through the experiments conducted by Robert A. Millikan. He is best known for his oil drop experiment, which provided precise measurements of the charge of the electron and demonstrated that charge is quantized.

5. **Recognition of Millikan's Work**: For his significant contributions to the understanding of electric charge and the quantization of charge, Millikan was awarded the Nobel Prize in Physics.

6. **Conclusion**: Therefore, the scientist who established that electric charge is quantized is R.A. Millikan.

**Final Answer**: R.A. Millikan

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