# Quantum Tunneling Question

1. Dec 9, 2013

### PsychonautQQ

1. The problem statement, all variables and given/known data
Calculate the reflection probability for a 5 eV electron encountering a step in which the potential drops by 2 eV

3. The attempt at a solution
To answer this question, wouldn't I need to know where E > U or U > E? Also wouldn't I need to know the width of the potential barrier it's trying to penetrate?

2. Dec 10, 2013

### Staff: Mentor

The way I understand the question is as follows:

Take the potential function
$$V(x) = \left\{ \begin{array}{ll} 0 & x \le 0 \\ - 2\text{ eV} & x > 0 \end{array} \right.$$
and consider an electron coming in from $x = -\infty$ with an energy of 5 eV.

3. Dec 10, 2013

### ShayanJ

From what you say,I see that you haven't understood the question,and so you can't get the answer.
An important point that seems you don't know,is that only potential energy difference has physical significance.So you can choose where the potential is zero arbitrarily and so a constant potential can always be called zero.The problem is saying that an electron is moving in a constant potential till it reaches a potential drop.So we can call the potential before the potential drop to be zero and negative after that.Also because no other change in potential is stated,we can assume that the potential is constant till it drops somewhere and then stays constant again and so there is no width.Also its not a potential barrier,you can call it a potential canyon,starting at the point of drop and continuing till infinity.