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The work functions (W(0)) of K, Na, Li, ...

The work functions `(W_(0))` of K, Na, Li, Mg and Cu are 2.25 , 2.30 ,2.42 ,3.70 and 4.80 eV respectively. How many of these metals do not undergo photoelectric effect when a radiation of wavelength 450 nm is allowed to fall on them ? (1eV = `1.602 xx 10^(-19) J) `

A

2

B

1

C

3

D

5

Text Solution

Verified by Experts

The correct Answer is:
A
`lambda= 450 ` nm
E = hv
or E = `h(c )/(lambda) implies 6.6xx10^(-34)Jsxx (3xx10^(8)m//s)/(450xx10^(-9)m)`
`E= 0.044xx10^(-17) or 4.4 xx10^(-19)J`
or ` E = (4.4xx10^(-19))/(1.602xx10^(-19))= 2.74 eV`
`[ because 1eV=1.602xx 10^(-19)]`
Thus K Na and Li which have less value of work functions `(W_(0))` than the energy of striking photon (E) , so can undergo photoelectric effect when radiation of wavelength 450 nm is allowed to fall on them.
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Knowledge Check

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