Question

In a photoelectric experiment using a CalciumCalcium surface, you find a stopping potential of 0.71 V for a wavelength of 347 nm and a stopping potential of 2.86 V for a wavelength of 217 nm.
Because this is an experiment, your value of Planck's constant will be slightly different from the official value.
From these data find
a) a value for Planck's constant h
__________________×10⁻³⁴J⋅s
b) the work function for CalciumCalcium
eVeV
c) the cutoff wavelength for this metal

Answer 1

a)

stopping potential,V1=0.71v for lambda1=347 nm

K.E1=0.71 ev

f1=C/lambda1

f1=3*10^8/(347*10^-9)

f1=0.864*10^15 Hz

stopping potential,V2=2.86v for lambda12=217 nm

K.E2=2.86 ev,

f2=C/lambda2

f2=3*10^8/(217*10^-9)

f2=1.38*10^15 Hz

use

by using Einstein's photoelectric equation,

h*f=W + K

===>

h=(K2-K1)/(f2-f1)

h=(2.86-0.71)*(1.6*10^-19)/((1.38-0.864)*10^15)

h=6.67*10^-34 J.sec

b)

work function, w=h*f1-K1

=((6.67*10^-34*0.864*10^15)-(0.71*1.6*10^-19))/(1.6*10^-19)

=2.892 ev

c)

w=h*C/lambda

2.892*1.6*10^-19=(6.67*10^-34*3*10^8)/(lambda)

lambda=4.324*10^-7 m

=432.4 nm