What is emitted by a hot metal filament in a cathode ray tube?
Correct answer: C. Electron.
- A. X-ray
- B. Proton.
- C. Electron.
- D. Photon.
Explanation
Heating the metal filament in the cathode ray tube causes an increase in energy of the filament which enables electrons to be released from the filament; this is called thermionic emission. This method is what JJ Thomson used for the discovery of electrons using the cathode ray tube experiment.
This question appeared on the UHS MDCAT 2008 paper, which you can sit online with every answer explained.
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About Quantum Theory and Radiation
Quantum theory treats electromagnetic radiation as packets of energy called photons, with energy proportional to frequency through E equals hf. The topic covers Planck's hypothesis, photon momentum, the photoelectric effect, threshold frequency, work function and wave particle duality, distinguishing quantised energy exchange from classical continuous radiation.
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