Chemistry · Structure Of Atom · NEET
Canal rays are beams of positively charged particles that form inside a discharge tube. When high voltage passes gas at low pressure, fast cathode rays (electrons) knock electrons out of the gas atoms. This leaves behind positive gas ions. These positive ions move towards the cathode. If the cathode has holes in it, some positive ions shoot through the holes and are seen behind it. These beams are the canal rays.
They are called canal rays because they pass through the canals (holes) made in the cathode. They are called anode rays or positive rays because they carry positive charge, like the anode. All three names mean the same thing. NCERT calls them canal rays carrying positively charged particles.
Cathode rays are negative (electrons) and move from cathode to anode; their properties do NOT depend on the gas used, so the electron is the same in every atom. Anode rays are positive and move towards the cathode; their mass and charge-to-mass ratio DO depend on the gas used. So each gas gives its own positive particle. This gas-dependence is the key exam point.
The proton was discovered from experiments on canal rays (E. Goldstein first observed the rays; the lightest positive particle from hydrogen gas was identified as the proton). Hydrogen is the lightest gas, so its positive ion is the smallest and lightest positive particle possible. This particle was named the proton. NEET usually just asks: proton was discovered from anode/canal ray experiments using hydrogen.
Cathode rays are electrons torn out of atoms, and the electron is identical in every atom, so its mass is always the same. Anode rays are the leftover positive gas ions, and different gases have different atoms, so the positive ions have different masses. Because hydrogen ion (a proton) is the lightest, hydrogen gives the particle with the largest charge-to-mass ratio.
Yes. In an electric or magnetic field, canal rays bend opposite to cathode rays. This proves they carry the opposite (positive) charge. Cathode rays bend towards the positive plate; anode rays bend towards the negative plate. This opposite deflection is a favourite one-line NEET fact.
No. Some positive ions carry one unit of positive charge, others carry a whole-number multiple of the fundamental charge (because an atom can lose one, two, or more electrons). NCERT states some particles carry a multiple of the fundamental unit of electrical charge. This is why the charge-to-mass ratio is not fixed for anode rays.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes, all three names refer to the same beams of positively charged gas ions produced in a discharge tube with a perforated cathode.
Hydrogen. Its positive ion is the lightest and smallest positive particle, and it was named the proton.
Yes. A proton is about 1836 times heavier than an electron, so hydrogen anode rays are much heavier than cathode rays.
Because the hydrogen positive ion (proton) has the smallest mass, the value of charge divided by mass (e/m) is the biggest for it among all gases.
Yes, in the absence of a field they travel in straight lines, but they move towards the cathode, opposite to cathode rays.
