The value of e/m of an electron was measured by:

Options

A. Millikan
B. J. Thomson
C. Dalton
D. utherford

Answer

To solve the question regarding who measured the value of e/m of an electron, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terms**:
- The term "e/m" refers to the ratio of the charge (e) of an electron to its mass (m). This ratio is significant in physics and chemistry as it helps in understanding the behavior of electrons in electric and magnetic fields.

2. **Identify Key Scientists**:
- Two prominent scientists are mentioned in relation to the study of electrons: Robert Millikan and J.J. Thomson.

3. **Robert Millikan's Contribution**:
- Millikan is known for his oil drop experiment, which was crucial in determining the charge of the electron. This experiment allowed him to measure the charge (e) accurately.

4. **J.J. Thomson's Contribution**:
- J.J. Thomson is credited with measuring the e/m ratio of the electron. He conducted experiments using cathode rays and demonstrated that electrons have a specific charge-to-mass ratio.

5. **Conclusion**:
- The scientist who measured the value of e/m of an electron is J.J. Thomson.

### Final Answer:
The value of e/m of an electron was measured by J.J. Thomson.

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