Julius Plücker and his student Johann Hittorf were experimenting with a Geissler tube. Plücker and Hittorf:
Placed two electrodes at each end of the tube
The positive plate was called the anode
The negative plate was called the cathode
Pumped all the air from the tube, creating a vacuum
Connected wires from the electrodes to a battery
(HOLD THE CURSOR OVER THE DIAGRAM TO VIEW THE GREEN GLOW )
Plücker and Hittorf discovered that when electricity flowed through the Geissler tube, a mysterious greenish glow was produced around the tube.
 | Sir William Crookes gained more knowledge about the mysterious green glow when he created a bent Geissler tube in 1875. He noticed that the glow was the most intense opposite the negative electrode, also called the cathode. Crookes reasoned that rays traveled from the cathode and then hit the end of the tube. Because of this, Crookes named these rays cathode rays. |
In later experiments Crookes placed barriers in the path of the cathode rays:
(HOLD THE CURSOR OVER THE DIAGRAM TO SEE THE RAYS TRAVEL)
Because a shadow was produced behind the barrier, Crookes reasoned that cathode rays:
- Acted like light
Seemed to travel in straight lines
Next, Crookes was able to change the path of the rays with a magnet. This meant:
- The cathode rays were NOT light (light is not affected my magnets or magnetic fields)
Cathode rays had some sort of charge
After further experiments, Crookes proved:
| 1) | All cathode rays have identical properties- the material the cathode is made of does not matter. |
| 2) | Cathode rays normally travel in straight lines perpendicular to the cathode. |
| 3) | Magnetic fields change the path of the cathode rays. (Crookes suspected that any charged object, not just magnets, could change the path of cathode rays.) |
| 4) | Rays caused reactions similar to those caused by light. |
| 5) | Scientists could not decide if cathode rays were electromagnetic waves of negatively charged particles. |
However, scientists could not decide if cathode rays were electromagnetic waves or negatively charged particles.
| PROPERTIES OF |
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