Work functions of tungsten and sodium are 4.4 eV and 2.3 eV respectively. If threshold wavelength of sodium is 5460 A, then threshold wavelength of tungsten is
(a) 11360 A
(b) 8000 Å
(c) 6000
Å
(d) 2840 A
o​

(d) 2840 A

Explanation:

Threshold frequency can be be calculated using expresion below

(λ)= hc/ Φ

(λ) sodium/ (λ)tungsten = Φtungsten/ Φsodium

But (λ) sodium is given as 5460 A,

Φsodium = 2.3 eV

Φtungsten= 4.4 eV

If we substitute the values we can find

(λ)tungsten.

(λ)tungsten= [(λ) sodium × Φsodium]/ Φtungsten

=( 5460× 2.3)/4.4

= 2854A

Hence, threshold wavelength of tungsten is 2854A

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