Why does a "crookes tube" produce an image at its' from end?

[mahela007]

According to the first two images of this wikipedia article

http://en.wikipedia.org/wiki/Crookes_tube

the anode of the crookes tube is situated ahead of the metal cross. Why do the electrons, which come out of the cathode, continue toward the cross to form an image behind it instead of heading straight for the +ve anode?

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29 views and no replies... Doesn't anyone know?

[swansont]

Because they miss the anode. They feel a force toward it, but force and velocity don't have to be in the same direction — the electrons will have some velocity orthogonal to the force, so they will have some lateral motion, and they miss.

[insane_alien]

much the same as various bits of debris in space are attracted towards the earth but they miss it.

[mahela007]

Is this attraction significant enough to cause a visible deviation in the path of electrons? It appears that the electrons (i.e the spark ) travel in a straight line.

[insane_alien]

yes it is although this depends on how far the phosphor is from the anode.

[swansont]

Is this attraction significant enough to cause a visible deviation in the path of electrons? It appears that the electrons (i.e the spark ) travel in a straight line.

 

Do a little back-of-the envelope calculation. Boltzmann's constant is of order 10^-4 eV/K, so thermal energy, even for something hot (1000K-ish), is significantly less than an eV. If the potential difference is even as small as a Volt, the energy from the apparatus is already noticeably larger than the thermal energy. 100V or 1000V? Of course it will look like it's moving in a straight line.

[UC]

why exactly is this in chemistry?