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Atomic Structure

Section: Chemistry

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Question : 1 of 32

Marks: +1, -0

The work functions (in eV ) of

\mathrm{Mg}, \mathrm{Cu}, \mathrm{Ag}, \mathrm{Na}

respectively are

3.7,4.8,4.3,2.3

. From how many metals, the electrons will be ejected if their surfaces are irradiated with an electromagnetic radiation of wavelength 300 nm ?

( h = 6.6 \times 10^{-34} \, \text{Js}, 1 \, \text{eV} = 1.6 \times 10^{-19} \, \text{J} )

[AP EAPCET 24 May 2025 S1]

1
4
2
3

Solution:

Using the formula,

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

The approx value of

h c = 120 \, \text{eV} \cdot \text{nm}

E = \frac{1240 \, \text{eV} \cdot \text{nm}}{300 \, \text{nm}} = 4.13 \, \text{eV}

For

\mathrm{Mg} : 4.13 \, \text{eV} > 3.7 \, \text{eV}

, so electron will be ejected

For

\mathrm{Cu} : 4.13 \, \text{eV} < 4.8 \, \text{eV}

, no electron ejected

For

\mathrm{Ag} : 4.13 < 4.3 \, \text{eV}

, no electron ejected

For

\mathrm{Na} : 4.13 > 2.3 \, \text{eV}

, so electron will be ejected

Thus, 2 metals will eject electron.

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