Atoms are electrically neutral. Hence after the discovery of the negatively charged constituent (electron) of an atom, attempts were made to discover the positively charged counterpart of electrons. By using a discharge tube containing a perforated cathode. Goldstein (1886) found that some rays passed through these holes in a direction opposite to that of the cathode rays.



                              Alt text: POSITIVE RAYS OR CANAL RAYS

These are called the positive rays or canal rays. J.J. Thomson (1910) measured their charge by mass ratio from which he was able to deduce that these contain positive ions. Their properties are:

  •  They are positively charged.

  •  The positive charge is either equal to or whole number multiple of the charge on an electron.

  •  When hydrogen gas was filled in the discharge tube the positive charge on the positive rays was equal to the negative charge on an  electron, and the mass was less than the hydrogen atom.

  •  Unlike cathode rays the properties of positive rays are characteristics of the gas in the tube.

  •  The deflection of positive rays under the influence of an electric or magnetic field is smaller than that of the cathode rays for the same  strength of field. This shows that the positive rays have a greater mass than that of electrons.

  •  The mass of the positive rays depends on the atomic weights or molecular weights of the gases in the discharge tube. The charge/mass  ratio also varies because the change in positive charge on the rays. It may be either equal to or integral multiple of the charge on an  electron.

  •  The lightest of all particles identified in positive rays from different elements was one with a mass very slightly less than that of hydrogen atom (or nearly equal to H-atom). The lightest positively charged particle is called a proton (P or P+). Positive rays are atomic or molecular resides from which some electrons have been removed. The removed electrons constitute the cathode rays and the positive residues form the positive or canal rays.


Positive Rays

Cathode Rays




O →



O2 →







The mass of a proton is very slightly less than that of a H-atom. This shows that protons are sub-atomic particles. Protons are fundamental constituent of matter because positive rays are produced by all substances.

“A sub-atomic particle, which is a fundamental constituent of all matter having a mass slightly less than that of H-atom and which carries a positive charge equal in magnitude to the charge on an electron, is called a proton”. A proton is denoted by p or p+ of +1p.

Comparison of Positive (Canal) Rays and Cathode Rays:


Cathode Rays

Canal Rays

Sign of Charge



Mag. of Charge

Always –1

Mostly +1, but also +2, +3…


Definite value

Variable, depends on ions


Definite value

Variable, depends on ions

Related Resources
Problems with Solutions

Problems with Solutions True and False Problem:...

Calculation of velocity of Electron

Calculation of Velocity: We know that mvr =...

Quantum Numbers

QUANTUM NUMBERS An atom contains large number of...

Atomic Models

Atomic Models We know the fundamental particles of...

Quantum Mechanical Model of Atom

Quantum Mechanical Model of Atom...

Discovery of Electron Proton and Neutron

Discovery of Electron, Proton & Neutron Lets...

Fundamental Particles


Relation-Kinetic Energy and Wavelength

Relation between Kinetic Energy and Wavelength:...

Atomic Spectrum

ATOMIC SPECTRUM If the atom gains energy the...

Wavelengths of Electromagnetic Radiations

Wavelengths of Electromagnetic Radiations:...

Atomic Structure Terms

ATOMIC TERM Nuclide: Various species of atoms in...

Hunds rule of Maximum Multiplicity

Hund’s Rule of Maximum Multiplicity: This...

Solved Questions of Atomic Structure Part I

Solved Questions of Atomic Structure Part I...

Radius and Energy Levels of Hydrogen Atom

Radius and Energy Levels of Hydrogen Atom:...

Dual Nature of matter and Photoelectric Effect

Dual Nature of Matter and Photoelectric Effcet...

Characteristics of Wave

Characteristics of Wave SOME IMPORTANT...

A-Scattering Experiment

A-Scattering Experiment Conclusions of...

Heisenbergs Uncertainty Principle


Bohrs Atomic Model

BOHR’S ATOMIC MODEL Bohr developed a model...

Calculation of Energy of Electron

Calculation of Energy of an Electron: The total...

Hydrogen Atom

HYDROGEN ATOM If an electric discharge is passed...

Objective Questions of Atomic Structure

Objective Questions of Atomic Structure Problem:...

Derivation of Angular Momentum from de Broglie Equation

Derivation of Angular Momentum from de Broglie...

Plancks Quantum Theory

PLANCK’S QUANTUM THEORY When a black body is...

Electronic Configuration

Electronic Configuration Rules for filling of...

Electromagnetic Radiations

Electromagnetic Radiations Some Important...

Discovery of Neutron

DISCOVERY OF NEUTRON After the discovery of...

Shapes and Size of Orbitals

Pauli’s Exclusion Principle: According to...

Limitations of Bohrs Theory

Merits of Bohr’s Theory: * The experimental...

Photoelectric Effect

PHOTOELECTRIC EFFECT Sir J.J. Thomson, observed...