Which of the following is never true for cathode rays?

Options

A. They possess kinetic energy
B. They are electromagnetic waves
C. They produce heat
D. They produce mechanical pressure.

Answer

To solve the question "Which of the following is never true for cathode rays?", we will analyze the properties of cathode rays based on the information provided.

### Step-by-Step Solution:

1. **Understanding Cathode Rays**:
- Cathode rays are streams of electrons emitted from the cathode in a vacuum tube. They are negatively charged particles.

2. **Kinetic Energy of Cathode Rays**:
- Cathode rays possess kinetic energy due to the motion of electrons. The kinetic energy (KE) of an electron can be expressed as:
\[ KE = \frac{1}{2} mv^2 \]
- Here, \(m\) is the mass of the electron and \(v\) is its velocity. Since cathode rays are composed of electrons, they indeed possess kinetic energy.

3. **Electromagnetic Waves**:
- One of the options states that cathode rays are electromagnetic waves. This statement is **not true**.
- Electromagnetic waves consist of oscillating electric and magnetic fields that are perpendicular to each other. In contrast, cathode rays do not exhibit this perpendicular relationship between electric and magnetic fields.

4. **Production of Heat**:
- Another option mentions that cathode rays produce heat. This statement is **true**.
- When cathode rays strike a metal surface, they transfer energy to the atoms in the metal, causing an increase in temperature (heat).

5. **Mechanical Pressure**:
- The final option states that cathode rays can exert high mechanical pressure. This is also **true**.
- Due to their high kinetic energy, cathode rays can exert pressure when they collide with surfaces.

6. **Conclusion**:
- Among the statements provided, the only statement that is never true for cathode rays is that they are electromagnetic waves.

### Final Answer:
The statement that is never true for cathode rays is: **They are electromagnetic waves.**