# When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is: Option 1) 0.65 eV Option 2) 1.0 eV Option 3) 1.3 eV Option 4) 1.5 eV

Let Initial energy was E.

Then abter increasing it by 20% it becomes 1.2 E .

Let work function is  $\Phi$.

Then   E- $\Phi$ = 0.5 ev ------------(1)

1.2 - $\Phi$ = 0.8 ev ------------(2)

or    $1.2.\left ( 0.5ev+\Phi \right )-\Phi =0.8ev$

$0.6ev+1.2\Phi -\Phi =0.8\:ev$

or $0.2\Phi = 0.2ev$

$\therefore \Phi = 1ev$

Option 1)

0.65 eV

Incorrect

Option 2)

1.0 eV

Correct

Option 3)

1.3 eV

Incorrect

Option 4)

1.5 eV

Incorrect

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