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 a straight route
• D. Cathode rays are fast electrons

Hint:

Cathode rays are streams of fast-moving electrons, not electromagnetic waves. They travel in straight lines unless influenced by electric or magnetic fields.

Answer 1

The Correct Option is B

Step 1: Understanding cathode rays. Cathode rays are streams of high-speed electrons emitted from the cathode in a vacuum tube. They possess mass and negative charge and exhibit particle-like properties. 

Step 2: Evaluating given statements. - (A) Cathode rays produce X-rays: Correct. When cathode rays strike a metal target, X-rays are generated due to energy conversion. 
- (B) Cathode rays are electromagnetic waves: Incorrect. Cathode rays are not electromagnetic waves; they are charged particles (electrons). Electromagnetic waves (like X-rays) have no charge or mass. 
- (C) Cathode rays travel in a straight route: Correct. In the absence of external magnetic or electric fields, cathode rays move in straight lines. 
- (D) Cathode rays are fast electrons: Correct. They consist of negatively charged high-speed electrons moving from the cathode to the anode. 

Conclusion. Since cathode rays are not electromagnetic waves, option (B) is incorrect, making it the correct answer for this question.

Answer 2

The question asks which statement about cathode rays is false. Cathode rays are streams of electrons emitted from a heated or high voltage cathode in a vacuum tube, so checking each statement against that particle nature identifies the false one.

1. Cathode rays produce X-rays: This statement is true. When fast moving cathode ray electrons strike a solid target, they decelerate suddenly and part of their kinetic energy converts into X-ray photons, the basic principle behind X-ray tubes.
2. Cathode rays are electromagnetic waves: This statement is false. Cathode rays are streams of electrons, particles that carry mass and negative charge and that get deflected by electric and magnetic fields. A true electromagnetic wave, such as light or an X-ray, has no mass or charge and travels independent of such fields. Because cathode rays behave as charged particles rather than as a wave of oscillating electric and magnetic fields, calling them electromagnetic waves is incorrect.
3. Cathode rays travel in a straight route: This statement is true. In the absence of an external electric or magnetic field, the electrons in a cathode ray beam move in straight lines from the cathode toward the anode, which is why they cast a sharp shadow of any object placed in their path.
4. Cathode rays are fast electrons: This statement is true. Cathode rays are, by definition, a beam of electrons accelerated to high speed between the cathode and anode inside an evacuated tube.

Three of the four statements correctly describe cathode ray behavior, while calling them electromagnetic waves contradicts their particle nature.

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