Another phy 4 Q

This question is from the unit 4 , Jan 2005 paper which i got from that school website.

One way to study the energy levels of an atom is to scatter electrons
from it and measure their kinetic energies before and after the collision.
If an electron of kinetic energy 0.92eV is scattered from a lithium atom
which is initially in the -5.02eV level, the scattered electron can have
only two possible kinetic energies.
State these two kinetic energy values, and explain what has happened to
the lithium atom in each case. (You should assume that the lithium atom
was at rest both before and after the collision.) [4]

Is this question set out correctly?

If it is can anyone please explain what we are supposed to do :s-smilie:

?

As i understand it we're supposed to find the kinetic energy of the scatterd electron but it's already given us the kinetic energy of the scatterd electron.

Reply 1

nas7232

yep you are right, therefore from the statement above

"State these two kinetic energy values"

state is the key word...

= 0.92ev [1 mark]

not sure about the second value though.

Reply 2

Paxi

yep quite a strange question ... i hope it's a one off.

Reply 3

Economist

A shockingly worded question and I still dont understand it after doing the paper in January

Reply 4

Felixa

Paxi

This question is from the unit 4 , Jan 2005 paper which i got from that school website.

Is this question set out correctly?

If it is can anyone please explain what we are supposed to do :s-smilie:

?

As i understand it we're supposed to find the kinetic energy of the scatterd electron but it's already given us the kinetic energy of the scatterd electron.

Our teacher went through this question with us. According to him (since he didn't have the actual markscheme) the answers are:

1) 0.92eV - There was no collision
2) 0.43eV - 0.49eV was absorbed so an Li electron could jump to the -4.53eV level. So the energy left is 0.92-0.49=0.43

Hope that helps! :smile:

Reply 5

Imaad

i have the mark scheme for that and it says

0.92ev

Atom stays in -5.02 level / nothing ahppens

0.43 ev

atom is excited to - 4.53 level

Reply 6

Imaad

and just a little rant that qu was really badly worded , it annoyed every1 when we did it in january. I got my script back and for the frist bit where u ahve to do the arrows, i did the corret arrows and didnt get the marks. but cant do ne thing bout it.

Reply 7

Felixa

Paxi

As i understand it we're supposed to find the kinetic energy of the scatterd electron but it's already given us the kinetic energy of the scatterd electron.

In answer to this bit. They've told you the KE of the scattered electron before it was scattered, and want you to state the two possible KEs after it's been scattered. I have to agree, they have worded it quite confusingly!