The scientist that performed the experiment on discharged tubes that led to the discovery of the cathode rays as a sub-atomic particle is

1. Analyze the question

The question asks for the specific scientist responsible for the experiment involving discharge tubes (also known as cathode ray tubes) that identified cathode rays as sub-atomic particles (specifically, electrons).

2. Explain the concept

In the late 19th century, scientists experimented with vacuum tubes (discharge tubes) to understand the nature of electricity. By applying a high voltage across electrodes in a vacuum, they observed a "glow" or rays emanating from the cathode.

• J.J. Thomson conducted experiments where he deflected these cathode rays using electric and magnetic fields. He concluded that these rays were composed of negatively charged particles, which he called "corpuscles" (later known as electrons).
• Robert Millikan is famous for the "Oil Drop Experiment," which determined the charge of a single electron.
• Ernest Rutherford is known for the "Gold Foil Experiment," which led to the discovery of the atomic nucleus.
• Niels Bohr proposed the model of the atom where electrons orbit the nucleus in discrete energy levels.

3. Show the solution

• Step 1: Identify the experiment described. The use of discharge tubes to study cathode rays is the hallmark of J.J. Thomson's research in 1897.
• Step 2: Evaluate the options. While other scientists contributed to atomic theory, Thomson is the one credited with the discovery of the electron through the cathode ray tube experiment.
• Step 3: Confirm the conclusion. Thomson's measurement of the charge-to-mass ratio of these particles proved they were sub-atomic particles smaller than the atom itself.

4. Identify the answer

The correct scientist is J.J. Thomson. This matches option A.

5. Tip for your exam

To remember this easily, use the mnemonic "Thomson's Tube". Whenever you see "Cathode Ray Tube" or "Discharge Tube" in a question, immediately associate it with J.J. Thomson and the discovery of the electron. If you see "Gold Foil," think of Rutherford and the nucleus!