Question

calculate the threshold frequency of metal if the binding energy of electron is 180.69kj/mole​

Answer 1

Threshold energy and binding energy are similar terms . Threshold energy is the amount of energy required to eject electrons from metal surface while binding energy is the amount of energy required to break the nucleus.

given, binding energy = 180.69 KJ/mole

1 mole = 6.023 × 10²³ electron

so, binding energy = 180.69 × 10³/6.023 × 10²³ J/atom

= 30 × 10^-20 J/electron .

hence, binding energy per electron , E = 3 × 10^-19 J

we know, from Plank's theory, E = hv, where h is Plank's constant and v is frequency.

experimentally, h = 6.63 × 10^-34 J.s

so, 3 × 10^-19 = 6.63 × 10^-34 × v

or, v = 3 × 10^-19/6.63 × 10^-34

≈ 0.45 × 10^15 Hz

≈ 4.5 × 10¹⁴ Hz

hence, threshold frequency is approximately 4.5 × 10¹⁴ Hz