Cathode Ray Tube
Definition and meaning of Cathode Ray Tube in chemistry.
Cathode ray tube (CRT) is an evacuated glass tube in which a heated cathode (negative electrode) emits a stream of electrons that accelerates toward an anode, producing a visible beam known as a cathode ray.
In more detail
When a high voltage is applied between two metal electrodes sealed inside a tube from which most of the air has been pumped out, electrons boil off the cathode and stream toward the anode, causing the residual gas or a phosphor-coated screen to glow along the path of travel. The rays travel in straight lines, cast sharp shadows, and are bent by both electric and magnetic fields toward the positive plate or pole, showing they carry negative charge. In 1897, J. J. Thomson used a cathode ray tube to measure the charge-to-mass ratio of these particles, proving they were far lighter than any known atom and identifying them as a new fundamental particle, the electron. This experiment overturned the idea of the atom as an indivisible sphere and opened the door to modern atomic theory.
Key facts
| Field | General Chemistry |
|---|---|
| Discovered particle | Electron (negatively charged) |
| Key experimenter | J. J. Thomson, 1897 |
| Core components | Evacuated tube, heated cathode, anode, phosphor screen |
J. J. Thomson applied perpendicular electric and magnetic fields across a cathode ray tube and adjusted their strengths until the beam's deflection was canceled out, allowing him to calculate the electron's charge-to-mass ratio (e/m) from the known field strengths and tube geometry.
Frequently asked questions
What are cathode rays actually made of?
Cathode rays are streams of electrons, negatively charged subatomic particles emitted from the heated cathode and accelerated toward the anode.
Why is the cathode ray tube significant in chemistry?
It provided the experimental evidence for the electron's existence, showing that atoms contain smaller charged particles and are not indivisible, which reshaped atomic theory.