# Potential Step-Down: Questions & Answers

• The thinker
In summary: First, you need to know the wave-function on the left side (before the step). Then you use the reflection theorem to find the wave-function on the right side. The reflection coefficient is simply the wave-function on the right side divided by the wave-function on the left side.
The thinker
Hi,

I'd just like to know if a beam will reflect when going over a down-step potential (from v=0 to v=-Vo)

Thanks.

What kind of beam? Please be more descriptive. Also, tell us what your thought are.

The question just says a beam of particles, I didn't think it mattered to be honest.

It's just the standard QM potential step but I don't know if the incoming wave will be reflected at all when giong down the step. Intuitively I'd say no... but then this is quantum mechanics so the answer is usually the option you least expected.

Ergo I expect the wave is completely reflected just because QM is odd and I figure this is the most unexpected answer. :)

Last edited:
The thinker said:
Intuitively I'd say no... but then this is quantum mechanics so the answer is usually the option you least expected.

Well, when a beam of photons passes through a pane of glass (we could treat the pane of glass as an increase in the potential of the photons - though this isn't entirely accurate, it does produce some of the results one would expect, i.e. diffraction, reflection, etc). If you've done about thin films and anti-reflective coatings, then you know that as the light exits it is also reflected a little (a lot if the angle is large enough).

So that's my intuition from something I observe physically, but quite why it's the case I'm unsure.

The thinker said:
The question just says a beam of particles, I didn't think it mattered to be honest.
It matters that it is a beam of particles. Then we know it is a standard QM problem.

It's just the standard QM potential step but I don't know if the incoming wave will be reflected at all when giong down the step. Intuitively I'd say no... but then this is quantum mechanics so the answer is usually the option you least expected.

Ergo I expect the wave is completely reflected just because QM is odd and I figure this is the most unexpected answer. :)
Since this is no way to answer the question (and you know it), why don't you do the next best thing: write down the most general form for the wave-functions on both sides and compute the reflection coefficient?

DeShark said:
Well, when a beam of photons passes through a pane of glass (we could treat the pane of glass as an increase in the potential of the photons - though this isn't entirely accurate, it does produce some of the results one would expect, i.e. diffraction, reflection, etc). If you've done about thin films and anti-reflective coatings, then you know that as the light exits it is also reflected a little (a lot if the angle is large enough).

So that's my intuition from something I observe physically, but quite why it's the case I'm unsure.
You can't solve problems by analogy or intuition when you don't know the limits of such analogy or intuition. In any case, you've picked the wrong analogy.

This is a straightforward QM problem and there is a standard approach to solving it.

## What is a potential step-down?

A potential step-down is a change in voltage or electric potential from a higher value to a lower value. This can occur in electrical circuits or systems.

## What causes a potential step-down?

A potential step-down can be caused by various factors, including the use of resistors, transformers, or voltage regulators. It can also occur naturally in electrical systems due to changes in load or other external influences.

## What are the applications of potential step-down?

Potential step-downs are commonly used in electrical systems to reduce the voltage to a desired level for specific applications. This can include powering electronic devices, stepping down high voltage power lines for distribution, or converting AC power to DC power.

## What are the effects of potential step-down on current?

A potential step-down can cause an increase in current, as the lower voltage allows for more current to flow through a given circuit. This can be beneficial in certain applications, but it is important to consider the potential effects on components and safety measures must be taken.

## How are potential step-downs calculated and controlled?

Potential step-downs can be calculated using Ohm's Law, which relates voltage, current, and resistance. They can be controlled using various devices such as resistors, transformers, or voltage regulators, depending on the specific application and desired outcome.

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