Question

What is the difference between cathode rays and beta rays since both are basically electrons?

Asked by: Kavita

 Answer

The two differently named 'rays' you mention not only consist of the same thing, note that they aren't even rays! Blame the imprecise labels partly on the fact that they were named before their true nature was understood.

Even before the electron was discovered, cathode 'rays' were observed in electrical experiments because of their fluorescent effect near a negatively charged plate (called the cathode) in a vacuum. They were only later found to be negatively charged electrons emitted from negatively charged plates and accelerating toward positively charged ones. (Like charges repel, unlike charges attract.)

Beta 'rays' were first observed being emitted from certain unstable (radioactive) isotopes, and behaved unlike the alpha and gamma radiation also found in radioactivity. It wasn't until later that both alpha and beta 'radiation' were discovered to actually be particles; only gamma rays consist of true electromagnetic radiation. Beta 'rays' are actually electrons ejected from decaying neutrons, and are now more often referred to as Beta emission or Beta particles.

So electrons can be described differently, not based on WHAT they are but HOW they are created or observed. You may want to add cosmic 'rays' to your list, which can also contain electrons coming to Earth from space! And what about 'static electricity', 'lightning', 'electric current', etc? Those electrons do get around, don't they? And if you think that only physics has imperfect nomenclature, ask a room full of astronomers whether Pluto is a planet or an asteroid!

Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

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