Which of the following statement is not correct about the characterstics of cathode rays

Options

A. They start from the cathode and move towards the anode.
B. They travel in straight line in the absence of an external electrical or magnetic field,
C. Characteristics of cathode rays do not depend upon the material of electrodes in cathode ray tube.
D. Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube.

Explanation

To determine which statement is not correct about the characteristics of cathode rays, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement:** Cathode rays start from the cathode and move towards the anode.
- **Explanation:** Cathode rays are indeed streams of electrons, which are negatively charged. They are emitted from the cathode (negative electrode) and are attracted to the anode (positive electrode). Therefore, this statement is correct.

### Step 2: Analyze Statement 2
**Statement:** Cathode rays travel in straight lines in the absence of an electrical or magnetic field.
- **Explanation:** In the absence of external forces, cathode rays (like electrons) will travel in straight lines. This is a fundamental property of particles with negligible mass and charge. Thus, this statement is also correct.

### Step 3: Analyze Statement 3
**Statement:** Characteristics of cathode rays do not depend upon the material of electrodes in the cathode ray tube.
- **Explanation:** The characteristics of cathode rays are indeed independent of the material of the electrodes. This is because all electrons, regardless of the source, have the same charge-to-mass ratio. Hence, this statement is correct.

### Step 4: Analyze Statement 4
**Statement:** Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube.
- **Explanation:** This statement is incorrect. The characteristics of cathode rays do not depend on the type of gas in the tube or the material of the electrodes. All gases consist of the same type of electrons, which have the same charge-to-mass ratio. Therefore, this statement is not correct.

### Conclusion
The statement that is not correct about the characteristics of cathode rays is:
**Option 4:** Characteristics of cathode rays depend upon the nature of gas present in the cathode ray tube.

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