Fundamentals of Electrification and Subatomic Particles

Understanding Electrification Phenomena

When rubbing certain materials, two electrical phenomena can be observed: attraction or repulsion. Charles inferred the existence of these two classes of electrical phenomena.

Electrification by Contact

This occurs when an isolated, uncharged body comes into contact with another body already charged by friction. To study this, we utilize an electric pendulum. These experiments show that bodies which have come into contact with other previously electrified bodies also become electrified.

Electrification by Induction

To electrify a body, it is not essential for the charged body to make direct contact with the body you wish to electrify (they can be closer but not touching).

Electric Charge: Definition and Properties

Electric charge is the amount of electric charge a body possesses and is measured in coulombs. Two bodies which have acquired the same charge repel each other, while those with different charges attract each other.

Unveiling Subatomic Particles

Electrification phenomena demonstrated that the atom consisted of other particles.

J.J. Thomson and the Electron

In 1897, J.J. Thomson investigated the conduction of electricity through gases. He utilized glass tubes fitted with metal plates (electrodes) which contained gas at very low pressure. He observed that when a high voltage was applied between the positive and negative metal plates, a weak fluorescent light appeared on the tube wall opposite the negative electrode, or cathode.

Thomson concluded that particles were emitted from the negative electrode, which he called cathode rays. He determined the charge-to-mass ratio (1.759 x 10¹¹ C/kg) of these negative particles. This ratio was constant and independent of the gas in the tube, demonstrating the existence of smaller particles, electrons, within atoms. (R. Millikan later determined the charge of an electron to be 1.602 x 10^-19 C).

E. Goldstein and the Proton

In 1886, E. Goldstein observed that if a gas discharge tube, similar to the one described above, had a perforated positive electrode (anode), another light appeared on the side opposite to the anode.

This light, named anode rays (or canal rays), was formed by positively charged particles. However, contrary to what happens with cathode rays, the particles forming these rays were not emitted from the anode itself but originated from the gas inside the tube. These positive particles found in the tube had the same magnitude of charge as the electron but a mass approximately 1836 times greater. These particles were later identified as protons.