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# Physics AS Help! watch

1. Hi guys can someone help me with the below:

The muon has a mass equal to 207 times the mass of an electron. Calculate the speed of muons with the same de Broglie wavelength as the electrons in part b (i.e. 1.6 × 10–9 m).

The answer is below but I was wondering if someone could explain why 1.6 × 10–9 m (the db wavelength from part b) becomes 1.6 × 10–7 ? and also why the answer is 2200. When I type in the same numbers into my calculator, I get 21.9737....

(207 × 9.11 × 10-31) × v = (6.63 × 10-34)/(1.6 × 10-7)
v = 2200 (2170)

If someone could explain this to me, I'd be so grateful! Thank you!
2. (Original post by juicedesuccess)
Hi guys can someone help me with the below:

The muon has a mass equal to 207 times the mass of an electron. Calculate the speed of muons with the same de Broglie wavelength as the electrons in part b (i.e. 1.6 × 10–9 m).

The answer is below but I was wondering if someone could explain why 1.6 × 10–9 m (the db wavelength from part b) becomes 1.6 × 10–7 ? and also why the answer is 2200. When I type in the same numbers into my calculator, I get 21.9737....

(207 × 9.11 × 10-31) × v = (6.63 × 10-34)/(1.6 × 10-7)
v = 2200 (2170)

If someone could explain this to me, I'd be so grateful! Thank you!
Do you understand the equations?

but

Do you have a screenshot of the question? When I use I get the correct answer.
3. (Original post by juicedesuccess)
Hi guys can someone help me with the below:

The muon has a mass equal to 207 times the mass of an electron. Calculate the speed of muons with the same de Broglie wavelength as the electrons in part b (i.e. 1.6 × 10–9 m).

The answer is below but I was wondering if someone could explain why 1.6 × 10–9 m (the db wavelength from part b) becomes 1.6 × 10–7 ? and also why the answer is 2200. When I type in the same numbers into my calculator, I get 21.9737....

(207 × 9.11 × 10-31) × v = (6.63 × 10-34)/(1.6 × 10-7)
v = 2200 (2170)

If someone could explain this to me, I'd be so grateful! Thank you!
v=h/mλ

It does not become 1.6 × 10–7.

Subbing in the de Broglie wavelength of the electrons you calculated before will give you the right answer.
4. Hi - thanks so much for your reply. Yes I understand the equations and the rearrangement of the equation - I just get stuck on why the de broglie wavelength has been multiplied by 100 in the question! Also I don't know how the answer of 2200 has been arrived at !! Mine is 21.9... even if I put in the figures as suggested in the answer!

I've attached a screen shot if that helps... Thank you!
Attached Images

5. (Original post by juicedesuccess)
Hi - thanks so much for your reply. Yes I understand the equations and the rearrangement of the equation - I just get stuck on why the de broglie wavelength has been multiplied by 100 in the question! Also I don't know how the answer of 2200 has been arrived at !! Mine is 21.9... even if I put in the figures as suggested in the answer!

I've attached a screen shot if that helps... Thank you!
I think it is a typo in the mark scheme if they are using 1.6 x 10^(-7), if you use 1.6 x 10^(-9) you get the correct answer! I tried myself.
6. (Original post by particlestudent)
v=h/mλ

It does not become 1.6 × 10–7.

Subbing in the de Broglie wavelength of the electrons you calculated before will give you the right answer.

Thank you!
7. (Original post by lizard54142)
I think it is a typo in the mark scheme if they are using 1.6 x 10^(-7), if you use 1.6 x 10^(-9) you get the correct answer! I tried myself.
Ah ok!!! Thank you! Stupid mark scheme! thanks again

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