Cathode rays, discovered in the late 19th century, are streams of electrons emitted from the cathode (negative electrode) of a high-voltage vacuum tube. These rays do not require a medium to propagate because they can travel through a vacuum. In fact, their discovery played a significant role in the understanding that electrons are fundamental particles that can exist and move independently of atoms or molecules. This characteristic distinguishes cathode rays from other forms of radiation like light or sound, which require a medium such as air or a solid material for transmission.
The conditions necessary for the generation of cathode rays include creating a high vacuum within the tube and applying a high voltage between the cathode and anode (positive electrode). When a sufficiently high voltage is applied, electrons are emitted from the cathode due to thermionic emission or field emission. These emitted electrons then accelerate towards the anode, forming a beam of cathode rays. The vacuum ensures that there are minimal collisions between electrons and gas molecules, allowing the electrons to travel freely in a well-defined path towards the anode.
Cathode rays do not significantly depend on the material of the cathode from which they are emitted. While different materials may have varying emission characteristics (such as work function or emission efficiency), once the electrons are emitted, their behavior in the electric and magnetic fields within the vacuum tube is primarily determined by their charge-to-mass ratio and the applied voltage. This property allows cathode rays to exhibit consistent behaviors and characteristics across different experimental setups and materials used for the cathode.
Cathode rays are composed of electrons, which are negatively charged subatomic particles. When accelerated by the electric field within the vacuum tube, these electrons form a beam that travels in a straight line from the cathode to the anode. The makeup of cathode rays therefore consists entirely of electrons moving at high velocities, typically approaching the speed of light under high acceleration voltages. Their properties, such as charge, mass, and ability to be deflected by electric and magnetic fields, align with the characteristics expected of electrons based on classical and quantum physics principles.