540 nm 2.60×10^(-20) J 400 nm 1.54×10^(-19) J

540 nm 2.60×10^(-20) J 400 nm 1.54×10^(-19) J

 

 

In the photoelectric effect, electrons are ejected

from a metal surface when light strikes it.

A certain minimum energy, Emin, is required to eject an electron.

Any energy absorbed beyond that minimum

gives kinetic energy to the electron.

It is found that when light at a wavelength of 540 nm

falls on a cesium surface, an electron is ejected

with a kinetic energy of 2.60×10^(-20) J.

When the wavelength is 400 nm,

the kinetic energy is 1.54×10^(-19) J.

(a) Calculate Emin for cesium in joules.

(b) Calculate the longest wavelength, in nanometers,

that will eject electrons from cesium.

 

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(a) Calculate Emin for cesium in joules.

 

E = hν = hc / λ

( 참고 https://ywpop.tistory.com/4964 )

 

= [(6.626×10^(-34) J•s) (2.998×10^8 m/s)] / [540 nm × (1 m / 10^9 nm)]

= (6.626×10^(-34)) (2.998×10^8) / (540 / 10^9)

= 3.68×10^(-19) J

 

 

 

E = KE + Φ = Ek + Emin

( 참고 https://ywpop.tistory.com/21474 )

 

Emin = E – Ek

= (3.68×10^(-19) J) – (2.60×10^(-20) J)

= 3.42×10^(-19) J

 

 

반응형

 

 

(b) Calculate the longest wavelength, in nanometers,

that will eject electrons from cesium.

 

λ = hc / E

= (6.626×10^(-34) J•s) (2.998×10^8 m/s) / (3.42×10^(-19) J)

= (6.626×10^(-34)) (2.998×10^8) / (3.42×10^(-19))

= 5.81×10^(-7) m

 

5.81×10^(-7) m × (10^9 nm / 1 m)

= 581 nm

 

 

 

답: (a) 3.42×10^(-19) J, (b) 581 nm

 

 

 

 

[ 관련 예제 https://ywpop.tistory.com/14353 ] Cs의 일함수. 400 nm 1.54×10^(-19) J. Cs에서 전자를 방출시킬 수 있는 빛의 최대 파장

 

 

 

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