Which scientist used the cathode ray tube to discover electrons and proposed the plum pudding model of the atom?

• A. Niels Bohr
• B. JJ Thomson
• C. Ernest Rutherford
• D. John Dalton

Answer: (B)

The key idea is how experimental evidence with a cathode-ray tube revealed subatomic particles called electrons and shaped early ideas about atomic structure. In these experiments, a beam travels from the negatively charged electrode toward the positive electrode and can be bent by electric and magnetic fields. The way the beam bends shows it carries negative charge, and measurements of its deflection indicate the particles have a very small mass relative to their charge. From this, a scientist proposed that atoms aren’t indivisible spheres after all, but contain these negatively charged electrons embedded in a positively charged material, like plums in a pudding. This is the plum pudding model, credited to JJ Thomson.

To place it in context, later experiments would push this picture aside in favor of a tiny nucleus, and other models emerged to explain how electrons are arranged around it. But the identification of electrons from cathode-ray experiments and the plum pudding proposal belong to Thomson, making him the correct figure for this question.