The Green Beam (Crookes Tube)
Takeaways / Key Ideas (TBD)
All atoms have identical, very low-mass, negatively charged particles that can leave atoms with changing the type of atom (properties are still the same).
All atoms have a positively charged part that is probably much, much more massive than the negatively charged particles that can leave the atom.
Student Models of Atoms (using conclusions from the Green Beam)
Crookes TubeCrookes Tube In Class
Crookes Tube Simulator
Same Force Applied, Different Changes in Direction
Crookes Tube Particle (cathode ray particle) compared to several atoms
The Crookes Tube (Green Beam)
In the first activity of the unit, students observed a Crookes tube in class (top video) and then used a simulator of the Crookes tube to gather additional data
OBSERVATIONS OF THE ACTUAL DEVICE (SEE TOP VIDEO)
In class we observed that the green beam that forms in the Crookes tube can be pushed or pulled by a magnet.
We also observed that a laser beam (light only) is not pushed or pulled by a magnet.
BACKGROUND KNOWLEDGE
When students did the simulator of the Crookes tube we discussed the following first:
The beam moves through a vacuum (there are no gases inside the device)
Because we know very little about batteries at the moment, we are viewing the battery as a device that only exerts electrical forces. Thus, the negatively charged disk will push on objects that are negatively charged and pull on objects that are positively charged. The positively charged plate will do the opposite. At this point in time we are not considering that anything is coming from or going to the battery.
OBSERVATIONS OF THE SIMULATION
After these items were discussed the students experimented with the simulator and noticed the following:
The beam always curves toward negative and away from positive
The beam always curves the same amount (if the force from the horizontal plates is constant)
The beam does not change (direction or amount of curve) even if the element that makes up the disks are changed from gold, to silver, to iron.
Unlike the negatively charged disk, nothing appears to leave the positively charged metal disk
The negatively and positively charged disks do not change in any noticeable way (get smaller or bigger, change color, etc...)
We also reviewed the Newtonian concept that when a force is applied to an object, the change in direction or speed of the object depends only on the mass of the object (mass goes up change goes down, mass goes down, change goes up). This concept was learned in sixth grade. We demonstrated it again with a fan and marbles of the same size but different mass (see video)
OBSERVATIONS OF CROOKES TUBE PARTICLES AND A HYDROGEN ATOM
Finally we compared the mass of the particles in the Crookes tube to the mass of the lightest atom (hydrogen)
OBSERVATIONS
The cathode ray particle changes direction way more than a hydrogen atom.
The force pulling / pushing on the cathode ray particle and the hydrogen atom were kept the same
