Values of work function (W_0) for a few metals are given below Metal Li Na K Mg Cu Ag W_0/eV 2.42 2.3 2.25 3.7 4.8 4.3 The number of metals which will show photoelectric effect when light of wavelength 400 nm falls on it is ___________ Given: h=6.6 x 10^-34 J s c=3 x 10^8 ms^-1 e=1.6 x 10^-19 C

E=(h c / lambda) =frac6.626 x 10^-34 x 3 x 10^8360 x 10^-9 =5.52 x 10^-19 J=frac5.52 x 10^-191.6 x 10^-19=3.45 eV Elements having W_0 less than 3.45 eV will show photoelectric effect. i.e., L i, N a, K => Three elements.

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Exam

Chemistry

Values of work function (W $_0$ ) for a few metals are given below

Metal	Li	Na	K	Mg	Cu	Ag
W $_0$ /eV	2.42	2.3	2.25	3.7	4.8	4.3

The number of metals which will show photoelectric effect when light of wavelength $400 \mathrm{~nm}$ falls on it is ___________

Given: $\mathrm{h}=6.6 \times 10^{-34} \mathrm{~J} \mathrm{~s}$

$c=3 \times 10^{8} \mathrm{~ms}^{-1}$

$e=1.6 \times 10^{-19} \mathrm{C}$

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Explanation

$E=\frac{h c}{\lambda} \\$

$=\frac{6.626 \times 10^{-34} \times 3 \times 10^8}{360 \times 10^{-9}} \\$

$=5.52 \times 10^{-19} \mathrm{~J}=\frac{5.52 \times 10^{-19}}{1.6 \times 10^{-19}}=3.45 \mathrm{eV}\\$ Elements having $W_0$ less than 3.45 eV will show photoelectric effect. i.e., $L i, N a, K \Rightarrow$ Three elements.