Photons and the photoelectric effect

  • Thread starter mandymanny
  • Start date
  • #1
mandymanny
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Homework Statement


the maximum wavelegnth for which an electromagnetic wave can eject electrons from a platinum surface is 196 nm. when radiation with a wavelength 141 nm shines on the surface, what is the max speed of the ejected electrons?


Homework Equations


f=c/λ
E=hf
E=Φ+K
Φ=hf0


The Attempt at a Solution


λ=196nm
f=(3E8)/(196E-9)
f=1.5306E15
E=Φ+K
(6.63E-34)(f??)=(Φ??)+K
K=??

λ=141nm
f=(3E8)/(141E-9)
f=2.127E15
E=Φ+K
(6.63E-34)(f??)=(Φ??)+K
K=??

K1-K2=_______
K=1/2mv^2 to find v


but i don't know what numbers to plug in as f?? and Φ??
i tried putting in the f values i found using the given wavelengths but i kept getting K=0

please help

thank you for your time
 

Answers and Replies

  • #2
EngageEngage
208
0
phi is the workfunction of the metal, which is related to the minimum wavelength required to eject an electron. If the energy input is the energy of the workfunction and nothing else, the kinetic energy will be zero of the electron
 
  • #3
sodr2
26
0
im having the same problem where I am supposed to find its max. kinetic energy of the photoelectron in electron volts(eV) and joules(J), but I am completely stuck.

if i use hf = Emax + work, i have planks constant (h) and frequency, but there are two variables left to find...please help me out
 
  • #4
alphysicist
Homework Helper
2,238
2
Hi sodr2,

im having the same problem where I am supposed to find its max. kinetic energy of the photoelectron in electron volts(eV) and joules(J), but I am completely stuck.

if i use hf = Emax + work, i have planks constant (h) and frequency, but there are two variables left to find...please help me out

If it's the same type of problem as in the original problem, use the equation twice. Once for the case of the maximum wavelength (and think about what being the maximum wavelength means for the other terms in the equation).

Then use it separately for the next given (smaller) wavelength to find the kinetic energy.

With two equations, you can have two unknowns. What do you get?
 

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