Which year did J. J. Thomson discover the electron?

Which year did J. J. Thomson discover the electron?

• A. 1897
• B. 1905
• C. 1911
• D. 1913

Answer: (A)

The key idea here is recognizing when scientists first demonstrated that electrons exist as a fundamental component of atoms. J. J. Thomson used a cathode-ray tube and found that the beam could be deflected by electric and magnetic fields in a way that revealed a tiny, negatively charged particle with a specific charge-to-mass ratio. The results were consistent across different gases, indicating a universal constituent of matter. From these experiments, he concluded that electrons exist and are part of all atoms, and he announced this in 1897. That makes 1897 the year associated with Thomson’s discovery. For context, the other years relate to different milestones in atomic theory and quantum science—for example, 1905 is tied to Einstein’s explanation of the photoelectric effect, 1911 to Rutherford’s discovery of the atomic nucleus, and 1913 to Millikan’s precise measurement of the electron’s charge.

The key idea here is recognizing when scientists first demonstrated that electrons exist as a fundamental component of atoms. J. J. Thomson used a cathode-ray tube and found that the beam could be deflected by electric and magnetic fields in a way that revealed a tiny, negatively charged particle with a specific charge-to-mass ratio. The results were consistent across different gases, indicating a universal constituent of matter. From these experiments, he concluded that electrons exist and are part of all atoms, and he announced this in 1897. That makes 1897 the year associated with Thomson’s discovery.

For context, the other years relate to different milestones in atomic theory and quantum science—for example, 1905 is tied to Einstein’s explanation of the photoelectric effect, 1911 to Rutherford’s discovery of the atomic nucleus, and 1913 to Millikan’s precise measurement of the electron’s charge.