1.33  [ENDORSED]


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204917020
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Joined: Fri Apr 06, 2018 11:05 am

1.33

Postby 204917020 » Thu Apr 26, 2018 4:57 pm

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x 10^3 km x s^-1.

a) what is the wavelength of the ejected electron?


In the solutions, they use lambda= h/mv. I just don't understand how the units for mass (kg) cancel out? There's not other mass units in the equation so how is kg not in the answer?

Tiffany Chen 1A
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Re: 1.33  [ENDORSED]

Postby Tiffany Chen 1A » Thu Apr 26, 2018 5:35 pm

There's a kg "hidden" in h. The units for h are J*s and a Joule is the same as kg*(m^2)*(s^-2). Taking this into account, the kg from h will cancel with the kg from mass, and the other units also cancel until you're left with meters.

Madison Hacker 1L
Posts: 30
Joined: Fri Apr 06, 2018 11:03 am

Re: 1.33

Postby Madison Hacker 1L » Sun Apr 29, 2018 5:27 pm

Remember that 1J is also equal to 1 kg x m^2 x s^-2 . This will help with problems that use the De Broglie equation because usually the Joule is at the numerator, and cancels with the denominator providing the unit you need.


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