Light of wavelength 380 nm is used in an experiment for photoelectrics. a)If 13×

Question

Light of wavelength 380 nm is used in an experiment for photoelectrics.

a)If 13×10^15 photons are emitted per second by this light source, calculate its
power (in watts).


b)It is found that on unknown metal X, only light of wavelength less than 380
nm ejects photo-electrons. Calculate the work function of this metal, in eV.

c)(4 points) When on metal X one uses light of wavelength 240 nm instead, what is the maximum kinetic energy, in eV, of the photo-electrons that are being ejected?

Lifesaver will be awarded

Explanation / Answer

( a )

E = n hv

E = n h c / ;  

E = 13 e 15 * 6.626 e -34 * 299792458 / 380e-9

P = 6.795 e -3 W <---------ans

( b )

hv = E ;

h c / = E ;

6.626 e -34 * 299792458 / 380e-9 = E ;

E in J = 5.227 e -19 J ;

E ( in eV ) = 5.227 e -19 / [1.6 e -19 ]

E in eV = 3.267 eV <------------ans

( c )

E = hv - hv0

E = hc ( 1 / - 1 / 0 ) ;

E = 6.626 e -34 * 299792458 ( 1 / 240e-9 - 1 / 380 e-9 ) ;

E = 3.049 e -19 J ;

E ( in eV ) = 3.049 e -19 / [1.6 e -19 ]

E ( in eV ) = 1.9058 eV <------------ans

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