Ionisation/Excitation caused by electron collisions

[physics369]

A few questions...

1) Does an electron have to have the exact amount of energy to cause excitation, or can it have more (i.e. can the eV of an incoming electron be equal or more than the excitation energy required for excitation of an atom to happen)? If so, does the electron that collided with the atomic electron keep the remaining energy?

2) When electrons have enough energy to excite atoms in a tube, why does the ammeter reading in the circuit decrease slightly? Is it because the electrons carry less KE after the collision and so travel slower?

3) When ionisation occurs near the anode (the metal plate that the electrons are traveling in the direct of), why is there a great increase in current? I thought it might be because there's now two sets of electrons traveling through the anode (the electrons that made the collision, and the electrons that were forced free from the gas atoms) or maybe because the liberated electrons are highly energized from the ionisation so they travel faster?

Any help would be appreciated!

 

[graphene]

Hello

A few questions...

1) Does an electron have to have the exact amount of energy to cause excitation, or can it have more (i.e. can the eV of an incoming electron be equal or more than the excitation energy required for excitation of an atom to happen)?

equal to or greater

If so, does the electron that collided with the atomic electron keep the remaining energy?

the colliding electron loses that much of energy (= excitation energy)
this is gained by the ionized electron and the atom.

2) When electrons have enough energy to excite atoms in a tube, why does the ammeter reading in the circuit decrease slightly? Is it because the electrons carry less KE after the collision and so travel slower?

There cathode is slightly negatively biased. So, when the potential difference reaches an excitation energy, the electron after excitation has very low KE to overcome the slight negative bias. So the current reduces.

Outside of this experiment, think of the tube being vacuum, the ammeter's reading is not related to the KE of electrons on the tube, it is a measure of the current in the circuit which would depend on the number of electrons ejected and not on their KE inside the tube.

3) When ionisation occurs near the anode (the metal plate that the electrons are traveling in the direct of), why is there a great increase in current? I thought it might be because there's now two sets of electrons traveling through the anode (the electrons that made the collision, and the electrons that were forced free from the gas atoms) or maybe because the liberated electrons are highly energized from the ionisation so they travel faster?

Any help would be appreciated!

your first guess is correct. second guess is wrong because, again current is not related to speed of electrons in the tube, it is related only to their number.