Same rays, any material

The idea

Cathode rays are the same whatever the cathode material or gas, so electrons are a fundamental component of all atoms; an electron's charge (–1.602 × 10⁻¹⁹ C) is taken as –1 by convention.

Change the metal, change the gas

In the cathode ray tube you can use different metals for the cathode and different gases inside the tube.

If the cathode metal or the gas is changed, what happens to the cathode rays?

• They stay the same kind of rays
• They turn into different rays for each metal
• They stop for every gas except one

Try different cathodes and gases

The labels Metal A, Metal B, Gas X and Gas Y are examples. Change the cathode and the gas.

Electrons are in all atoms

The rays did not change with the metal or with the gas. So electrons are a part of the atoms of every element.

The nature of cathode rays is independent of the cathode material and the gas in the tube. So electrons are a fundamental component of all atoms, present in every element. The charge of an electron (−1.602 × 10⁻¹⁹ C) is taken as −1 as a matter of convention and convenience.

Notes

The nature of cathode rays does not depend on the cathode or the gas, so electrons are in all atoms. An electron's charge (−1.602 × 10⁻¹⁹ C) is taken as −1 by convention.

Check yourself

Cathode rays are the same for different cathode materials. What does this show?

By convention, the charge of an electron is taken as …

When the gas in the tube is changed, the cathode rays …

• Electrons are a component of the atoms of all elements — correct. Yes!
• Only the metal used as the cathode contains electrons. The rays were the same for every cathode material, so electrons are not special to one metal.
• Electrons come from the gas alone. The rays were the same when the gas was changed, so electrons do not belong to one gas alone.
• +1. A positive charge would be +1, but an electron carries negative charge.
• −1 — correct. Yes!
• 0. Zero means no charge, but an electron is charged.
• become positively charged. The rays remain streams of negatively charged particles.
• change into a different kind of particle. The nature of cathode rays is independent of the gas filled in the tube.
• stay the same in nature — correct. Yes!