Chemistry · Structure Of Atom · NEET
Cathode rays are made of electrons. They are a stream of tiny, fast-moving, negatively charged particles. When you apply high voltage to gas at low pressure, these electrons break free and shoot across the tube. Because they always behave the same no matter which gas or metal you use, we say electrons are a basic part of every atom. This is the key point NEET wants you to remember.
The cathode is the negative electrode and the anode is the positive electrode. Electrons carry a negative charge. Opposite charges attract and like charges repel. So the negative cathode pushes the electrons away, and the positive anode pulls them in. That is why the rays always travel from cathode to anode, giving them their name.
At normal pressure there are too many gas molecules in the way. The electrons keep hitting them and cannot travel across the tube, so no current flows. When you pump most of the gas out (low pressure), the electrons have a clear path and can move freely from cathode to anode. NEET note: you need BOTH low pressure AND high voltage together for cathode rays to appear.
When you put an electric field or a magnetic field near the tube, the rays bend. They bend in the exact direction you would expect for negative particles: they move toward the positive plate. This proves the rays carry negative charge. In the absence of any field, they travel in a straight line, which also proves they are real particles with momentum.
No. This is a favourite NEET trap. The properties of cathode rays (electrons) do NOT depend on the gas filled in the tube or the metal used for the electrodes. You always get the same electrons with the same charge-to-mass ratio. This sameness is the proof that electrons are present in ALL atoms.
The rays themselves are invisible. To detect them, the tube is coated with a fluorescent or phosphorescent material like zinc sulphide. When the rays hit this coating, it glows and makes a bright spot. Old television and computer picture tubes worked exactly this way, they were cathode ray tubes.
Cathode rays travel from cathode to anode and are made of electrons (negative). Canal rays (anode rays) travel the opposite way and are made of positive ions. Also, cathode ray properties never change with the gas, but canal ray properties DO depend on the gas used. Canal rays led to the discovery of the proton, a separate concept.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The study of cathode rays began in the 1850s with scientists like Faraday. J.J. Thomson later studied them in detail in 1897 and identified the electron by measuring its charge-to-mass ratio. So cathode rays led directly to the discovery of the electron.
They travel in a straight line from the cathode (negative electrode) to the anode (positive electrode) when no field is applied. In an electric or magnetic field they bend like negative particles.
Because cathode rays are always identical no matter which gas or metal you use. Since the same electrons come out of every material, electrons must be a basic building block present in all atoms.
Yes. In the absence of any electric or magnetic field, cathode rays move in a straight line. This is shown when they cast a sharp shadow of an object placed in their path.
Two conditions together: very low gas pressure inside the tube and very high voltage across the electrodes. Only then do the electrons flow across as cathode rays.
