## Problem 1B.20

$\lambda=\frac{h}{p}$

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Maya Johnson 2a
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Joined: Wed Sep 30, 2020 9:47 pm

### Problem 1B.20

Hi, I have having issues with problem 1B.20 from the book:
What is the wavelength of an electron when the distance it travels in 1 s is equal to its wavelength?
and was wondering how I should set up this problem?

Mahnoor_Wani_1I
Posts: 123
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### Re: Problem 1B.20

The Debroglie equation tells us that wavelength = h/mv
Since the question states that velocity (distance/sec) is equal to the wavelength, we substitute velocity for wavelength.
V = h/mv

Isolate the V
V^2 = h/m
V= sqrt(h/m)

Plug in the planks constant and the mass of an electron, which is also a constant
v = sqrt(6.626*10^-34 J*s / 9.109*10^-31 kg)
v = 0.027 m/s

Since the velocity = wavelength
wavelength is 0.027 m

Isaac Wen
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### Re: Problem 1B.20

Just out of curiosity, if the question were to replace 1s with another quantity of time, we just have to multiply the velocity we get by the quantity asked to find the wavelength right?

Brandon Le 3C
Posts: 89
Joined: Wed Sep 30, 2020 9:49 pm

### Re: Problem 1B.20

Isaac Wen wrote:Just out of curiosity, if the question were to replace 1s with another quantity of time, we just have to multiply the velocity we get by the quantity asked to find the wavelength right?

Yes, we would multiply the given quantity of time by the velocity, and set that equal to wavelength instead. For example, if it was 2s instead of 1s, wavelength = 2V, so 2V = h/mv. Then just isolate V again and solve.

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