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 ligh

Question

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 × 10 – 34 J s c = 3 × 10 8 ms – 1 e = 1 . 6 × 10 – 19 C

TestHub · Accepted Answer

The minimum amount of energy necessary to start the emission of electrons from a metal's surface is known as its work function. The work function is the minimum amount of energy required to remove an electron from a metal's surface to infinity.

Energy of incident photon $= \frac{h c}{λ}$

$= \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{400 \times 10^{- 9}} J$

$= \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{400 \times 10^{- 9} \times 1.6 \times 10^{- 9}} eV$

$= 3.1 eV$

If radiation energy is greater than work function of metal, then metal show photo electric effect.

$∴ Li, Na$ and $K$ will show photoelectric effect.

Metal	$Li$	$Na$	$K$	$Mg$	$Cu$	$Ag$
$\frac{W_{0}}{eV}$	$2.42$	$2.3$	$2.25$	$3.7$	$4.8$	$4.3$

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