Solve Stopping Potential when 250 nm Light Hits Zinc Plate

[Tsunoyukami]

Homework Statement

I'm doing some practice problems for an introductory quantum mechanics course and am unsure whether or not I'm solving this problem properly - I need confirmation if I'm doing it right and help if I'm doing it wrong! :)

"What is the stopping potential when 250 nm light strikes a zinc plate?" (Chapter 3, #18 in Modern Physics 2nd ed. by Randy Harris)

Homework Equations

K = E - \varphi (where K is the kinetic energy, E is the energy of the incident light and \varphi is the work function)

This can be written as:

\frac{mv^2}{2} = \frac{hc}{\lambda} - \varphi (where m is the mass of a scattered electron, v is the speed of this electron, h is Planck's constant and c is the speed of light)

\frac{mv^2}{2} = qV (where q is the electron charge and V is the stopping potential)

h = 6.626 x 10^(-34) Js
c = 3 x 10^8 m/s
\varphi = 4.3 eV

The Attempt at a Solution

If my equations above are correct, I can write:

\frac{mv^2}{2} = \frac{hc}{\lambda} - \varphi = qV
\frac{hc}{\lambda} - \varphi = qV
V = \frac{\frac{hc}{\lambda} - \varphi}{q}

I can then simply plug in my values (remembering to either convert h in eV*s or \varphi into J) and this should give me the stopping potential, correct?

 

[Delphi51]

Yes, that all looks good. No quantum mechanics in there, though; its all high school physics.

 

[Tsunoyukami]

Thanks! And you're right, there isn't really any quantum mechanics here; it's just included in part of the course and its part of the introduction leading into the actual quantum mechanics.