[suneilr]

I was just looking over my notes for quantum mechanics and I came across the step potential.
I have that the reflection coefficient from the step for E<V0 is 1 ie all particles are definitely reflected from the step. I'm a little confused since there is a small but finite probability of finding the particle beyond the step. I can't quite reconcile these two facts in my mind. Help would be much appreciated thanks

EDIT: Ok hmm I've found source that says that an incoming particle beam penetrates the step slightly but is then completely reflected. Can anyone confirm that this is the correct interpretation?

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[Hellier]

Originally Posted by suneilr

I was just looking over my notes for quantum mechanics and I came across the step potential.
I have that the reflection coefficient from the step for E<V0 is 1 ie all particles are definitely reflected from the step. I'm a little confused since there is a small but finite probability of finding the particle beyond the step. I can't quite reconcile these two facts in my mind. Help would be much appreciated thanks

EDIT: Ok hmm I've found source that says that an incoming particle beam penetrates the step slightly but is then completely reflected. Can anyone confirm that this is the correct interpretation?

Don't worry, it's just barrier tunneling. The particle shouldn't be able to get through the barrier, but there is a chance that it does. That's quantum mechanics for you

[suneilr]

Originally Posted by Hellier

Don't worry, it's just barrier tunneling. The particle shouldn't be able to get through the barrier, but there is a chance that it does. That's quantum mechanics for you

Its not tunnelling though since the reflection coefficient is 1, which is what I was initially confused about...

[Hellier]

but it's impossible that ALL particles are reflected back from the step. There will always be an amplitude for barrier tunnelling.

[suneilr]

Thats only the case for the barrier potential not the step potential. I understand (I think) the barrier potential case. Its just the step potential I'm still a little unclear on.

[Hellier]

the probability of an event occuring is that event's amplitude divided by the sum of all possible events. perhaps that is where the problem is arising from.

[Mehh]

Okay...This is simple enough.

Classically all of the wave is reflected.
In the Quantum Physics representation it is also completely reflected. But what the small finite effinecient wave shows is WHERE its reflected from.

Some of the wave penitrates into the step a little before it is reflected.

You can see this if you cut a thin slice of the barrier again.

This time if you do the maths, not all of the wave is reflected, only some. Some of it 'tunnels' through and isn't reflected by the material.

[MC REN]

Pretty much what he^ said but...

*evanescent wave* (not effinecient)

And this evanescent wave carries no power, so all the power is reflected

(in a non-infinite barrier some power is carried because we need have a sum of say two evanescent waves so there is some transmission)