Question

The e/m ratio for cathode rays:

• A. is constant
• B. varies as the atomic number of the element forming the cathode in the discharge tube changes
• C. varies as the atomic number of the gas in the discharge tube varies
• D. has the smallest value when the discharge tube is filled with hydrogen

Answer 1

The correct option is A is constant

The e/m ratio for cathode rays is constant. It is equal to $1.76\times {10}^{8}C/g$. It is independent of the nature of gas in discharge tube and nature of cathode or electrodes of tube. This shows that an electron is a universal fundamental particle.