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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.
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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 |
Electromagnetic Waves |
Negatively Charged Particles |
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Travels in straight lines
Causes
chemical changes
(These are also properties of light and light is an electromagnetic wave.) |
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Magnetic fields known to deflect
negative particles |
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