Cathode rays are

Analysis of the Question

The question asks for the fundamental nature of cathode rays. To answer this, we need to look at the historical discovery of cathode rays and their physical properties observed in discharge tubes.

Concept Explanation

Cathode rays were discovered during experiments with vacuum tubes (discharge tubes). When a high voltage is applied across electrodes in a low-pressure gas, a beam of particles is emitted from the cathode (the negative electrode) and travels toward the anode (the positive electrode).

Key characteristics of cathode rays include:

1. Charge: They are deflected by electric and magnetic fields in a way that indicates they are negatively charged.
2. Mass: They possess mass, which was proven by their ability to rotate a small paddle wheel placed in their path.
3. Identification: J.J. Thomson, through his famous experiments, identified these particles as electrons.

Step-by-Step Solution

1. Evaluate Option A: Electromagnetic waves (like X-rays or Gamma rays) are not deflected by electric or magnetic fields. Since cathode rays are deflected, they cannot be electromagnetic waves.
2. Evaluate Option B: Protons are positively charged particles. Cathode rays are negatively charged, so this is incorrect.
3. Evaluate Option C: Neutrons have no charge. Cathode rays are charged, so this is incorrect.
4. Evaluate Option D: Cathode rays are produced at the cathode and consist of a beam of negatively charged particles. These particles are electrons.

Conclusion

Based on the physical properties of cathode rays, they are confirmed to be streams of electrons moving at high speeds.

Exam Tip: Always remember the mnemonic "Cathode = Negative". Since cathode rays originate from the cathode, they must be negatively charged. Since electrons are the primary negatively charged subatomic particles in these tubes, cathode rays are simply streams of electrons.