Post-Module Assessment Q. 34

[William Lan 2l]

If an electron (mass 9.11 x 10^-31 kg) has an associated wavelength of 7.28 x 10^-9 m, what is its speed? Is your answer reasonable, why?

A. 1.00 x 10-5 m.s-1. Yes. 1.00 x 10-5 m.s-1 is reasonable for e- as it is less than the speed of light, c = 3.0 x 108m.s-1.

B.1.00 x 10-5 m.s-1. No. 1.00 x 10-5 m.s-1 is not reasonable for e- as it is significantly slower than the speed of light, c = 3.0 x 108 m.s-1.

C. 1.00 x 105 m.s-1 . Yes. 1.00 x 105 m.s-1 is reasonable for e- as it is less than the speed of light, c = 3.0 x 108m.s-1.

D. 1.00 x 105 m.s-1. No. 1.00 x 105 m.s-1 is not reasonable for e- as it is significantly slower than the speed of light, c = 3.0 x 108 m.s-1.

So how exactly do you do this problem? I used lambda = h/mv equation and I switched it around so that v= h/(m x lambda). When I solved for V, I got 99939 m/s, which is none of the answers.

[Chem_Mod]

When you do the calculation you did, you should get 1*10^5 m/s which is one of the answers given. Your formula is correct, but there is a mistake with the calculation.

[Yashaswi Dis 1K]

I think your answer is like correct, meaning approx. close to the answers given b/c when you round the answer you got and change it to scientific notation, you should get 1.00 * 10^5 m/s and since it's way less than speed of light, which if the fastest speed known so far, answer should be reasonable. Again, check the video module maybe because it has more specifics on that. Hope this helps!

[Lily Guo 1D]

I think your answer is like correct, meaning approx. close to the answers given b/c when you round the answer you got and change it to scientific notation, you should get 1.00 * 10^5 m/s and since it's way less than speed of light, which if the fastest speed known so far, answer should be reasonable. Again, check the video module maybe because it has more specifics on that. Hope this helps!

How do you know that the speed of the electron is reasonably fast or not? Is there a specific range of values that the speed should fall in? I got ~1.00 x 10^5 m/s, I'm just not sure if this is a reasonable speed or not since it's so much less than the speed of light.

[Yashaswi Dis 1K]

I am not exactly sure but as far as I know, the speed of light is the fastest speed on earth, unless research shows otherwise. Thus, if you get a speed less than 3.00 * 10^8 m/s, I am pretty sure it's reasonable b/c it's less than speed of light, which is the fastest speed known so far. That's my thought process when I answered the module questions and it helped me out...so hope this helps!