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Difficulty: EasyConduction of Electricity Through Gases and Cathode Rays

Which of the following observations demonstrates that cathode rays possess kinetic energy and momentum?

  1. The rotation of a light paddle wheel placed directly in their pathAnswer
  2. B
    The casting of a sharp shadow when an opaque Maltese cross is placed in their path
  3. C
    The production of fluorescence when the rays strike the glass walls of the discharge tube
  4. D
    The deflection of the rays toward a positively charged plate in an electric field

Answer

The rotation of a light paddle wheel placed directly in their path
Cathode rays consist of high-speed electrons possessing mass and kinetic energy. When these particles strike the vanes of a light paddle wheel inside a discharge tube, they transfer mechanical momentum to the wheel, causing it to roll along the glass rails. This directly proves that the rays carry kinetic energy and momentum.

Step-by-Step Solution

1
Recall the physical properties of cathode rays evidenced by classical discharge tube experiments.
Cathode rays travel in straight lines, carry negative charge, produce fluorescence, and possess mechanical momentum.
Identifying the specific experimental evidence associated with kinetic energy and momentum.
2
Analyze the mechanical effect of particle bombardment on a physical object in a vacuum tube.
When stream particles strike the blades of a lightweight paddle wheel, they exert a mechanical force that causes the wheel to turn.
Transfer of momentum (Δp\Delta p) upon collision converts particle kinetic energy (Ek=12mv2E_k = \frac{1}{2}mv^2) into rotational kinetic energy of the paddle wheel.

Key Concept

Particle Nature and Mechanical Energy of Cathode Rays
Estimated Time:45s
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Topics

Conduction of Electricity Through Gases and Cathode Rays

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