Question

Choose the incorrect statement regarding Cathode rays:

• A. Cathode rays produce X-rays
• B. Cathode rays are electromagnetic waves
• C. Cathode rays travel in straight route
• D. Cathode rays are fast electrons

Answer 1

The Correct Option is B

The correct option is (B): Cathode rays are electromagnetic waves.

Answer 2

Cathode rays are streams of electrons emitted from the cathode of a discharge tube, and their properties follow from being charged particles rather than waves. Each statement can be tested against this:

1. Cathode rays produce X-rays: When fast-moving cathode ray electrons strike a metal target (as in an X-ray tube), their sudden deceleration produces X-rays. This statement is correct.
2. Cathode rays are electromagnetic waves: Cathode rays consist of negatively charged particles (electrons) possessing mass and momentum; they are deflected by electric and magnetic fields in a way only charged particles are. Electromagnetic waves, like light or X-rays, are uncharged and are not deflected by such fields. Since cathode rays behave as charged particles and not as electromagnetic radiation, this statement is false.
3. Cathode rays travel in straight route: In the absence of external fields, cathode rays travel in straight lines from the cathode, which is why they cast sharp shadows of objects placed in their path. This statement is correct.
4. Cathode rays are fast electrons: Cathode rays are indeed streams of electrons accelerated to high speed by the potential difference in the discharge tube. This statement is correct.

Since cathode rays are particulate (electrons) and not electromagnetic radiation, the claim that they are electromagnetic waves is the false statement among the four.

Therefore, the correct answer is Cathode rays are electromagnetic waves.