## General Heisenberg Question

$\Delta p \Delta x\geq \frac{h}{4\pi }$

Stella Nguyen 1J
Posts: 63
Joined: Wed Sep 30, 2020 9:41 pm

### General Heisenberg Question

Hi everyone!

In Heisenberg problems, will there be instances where we're given a +/- with a percentage? For example, can the problem give us an uncertainty for position as 5.00 +- 1%, or would there always be an actual number after the +- sign? I understand that in theory, we would have to double it to 2%, and if there are questions like this, would the uncertainty for position in this situation be 0.02?

Thank you so much!

DanielHong2L
Posts: 55
Joined: Wed Sep 30, 2020 9:51 pm

### Re: General Heisenberg Question

Stella Nguyen DIS 1J wrote:Hi everyone!

In Heisenberg problems, will there be instances where we're given a +/- with a percentage? For example, can the problem give us an uncertainty for position as 5.00 +- 1%, or would there always be an actual number after the +- sign? I understand that in theory, we would have to double it to 2%, and if there are questions like this, would the uncertainty for position in this situation be 0.02?

Thank you so much!

I cannot comment on future instances of being given +/- i have no clue. However, if it's given as a plus/minus, it should have a number. And the uncertainty, if given as a percentage would be 5.00 * .01 * 2

This is beacuse it's +/- 1 percent of 5 (so mutliply by .01), and its +/- (so multiply by 2) to get the delta x

Yun Su Choi 3G
Posts: 61
Joined: Wed Sep 30, 2020 10:09 pm

### Re: General Heisenberg Question

I am not 100% sure, but based on most of the Heisenberg questions we practiced with, the uncertainty was expressed in actual values with units. I don't think I have seen a question with plus or minus percentages.

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Joined: Wed Sep 30, 2020 9:41 pm
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### Re: General Heisenberg Question

Hi, so you could definitely see a problem where a +/- is given with a percentage. In this case, you would have to double the percentage value as you have been doubling uncertainities after the +/-. You just need to then multiply this doubled value of the percentage to the value, which in your case, is 5.00. The uncertainty would not be 0.02, but it would be 2% of 5.00, or 0.1.

We double the percentage and multiply it to the original value because the percentage is telling you that it is the uncertainty of the value they give you. The percentage must be doubled because the +/- indicates that it could be 0.01% of 5.00, or 0.05, above 5.00 or below 5.00. The percentage needs to then be applied to the original value, 5.00, because the uncertainty in position is a percentage of the position. In other cases, where you are not given the percentage, then those values already take into consideration the uncertainty value. A percentage itself cannot be the uncertainty because it is disregarding the value (5.00) you were given.

Hope this helps!

Brianna Chen 3F
Posts: 64
Joined: Wed Sep 30, 2020 10:11 pm

### Re: General Heisenberg Question

When dealing with percentages in uncertainty, you would have to take that percentage amount of the value given (not just take the percentage as the uncertainty value). Therefore, you would take 2% of 5.00 for the example you gave which will give you your uncertainty value.

Catherine Bubser 2C
Posts: 67
Joined: Wed Sep 30, 2020 9:45 pm

### Re: General Heisenberg Question

In regards to uncertainty in position, do we need to multiply the position by 2? On sapling, I did not need to change delta x but I did have to multiply delta x by 2 in some step-up sessions. How do we know when to do this?

Isabella Cortes 2H
Posts: 60
Joined: Wed Sep 30, 2020 9:37 pm

### Re: General Heisenberg Question

When you are given a percentage as your uncertainty you would have to multiply the percentage by the position value, to get your uncertainty. So in the example you gave, the uncertainty in position would be (.02)(5)= .1.

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Joined: Wed Sep 30, 2020 9:36 pm
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### Re: General Heisenberg Question

Catherine Bubser 2C wrote:In regards to uncertainty in position, do we need to multiply the position by 2? On sapling, I did not need to change delta x but I did have to multiply delta x by 2 in some step-up sessions. How do we know when to do this?

Hi! I believe it ultimately depends on what the question is asking. You have to multiply by 2 when something says "+ or -". This is because the change can happen in the positive or negative direction. Another time I remember having to multiply by 2 is when a problem gave the radius, but we needed the diameter in order to have the uncertainty in position. I wouldn't say there is necessarily a set rule on when to multiply by 2. You just have to really read the question carefully. Hope this helps! :)