1.33 [ENDORSED]

[204917020]

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]

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]

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.