The e/m value for cathode rays

Options

A. varies with the nature of the gas
B. does not vary with the nature of gas
C. could not be determined by J J . Thomson
D. nucleons

Answer

To find the e/m value for cathode rays, we can follow these steps:

### Step 1: Understand the Components
The e/m value refers to the ratio of the charge (e) of an electron to its mass (m). For cathode rays, which are streams of electrons, we need to use the known values of the charge and mass of an electron.

**Hint:** Remember that the charge of an electron is negative, but for calculating e/m, we will use the absolute value.

### Step 2: Identify the Charge of an Electron
The charge of an electron (e) is approximately:
\[ e = -1.6 \times 10^{-19} \text{ coulombs} \]

**Hint:** Focus on the magnitude of the charge for this calculation.

### Step 3: Identify the Mass of an Electron
The mass of an electron (m) is approximately:
\[ m = 9.1 \times 10^{-31} \text{ kg} \]

**Hint:** Make sure to use the correct units for mass.

### Step 4: Calculate the e/m Ratio
Now, we can calculate the e/m ratio using the formula:
\[ \frac{e}{m} = \frac{1.6 \times 10^{-19}}{9.1 \times 10^{-31}} \]

**Hint:** When performing the division, ensure you keep track of the scientific notation.

### Step 5: Perform the Calculation
Calculating the above expression:
\[ \frac{e}{m} = \frac{1.6 \times 10^{-19}}{9.1 \times 10^{-31}} \approx 1.758 \times 10^{11} \text{ C/kg} \]

**Hint:** The result will be a constant value, which is characteristic of electrons.

### Step 6: Conclusion
The e/m value for cathode rays (electrons) is approximately:
\[ \frac{e}{m} \approx 1.758 \times 10^{11} \text{ C/kg} \]

**Hint:** This value does not depend on the type of gas used in the cathode ray tube.