Answer:
1. λ = 2.626 x 10⁻⁷ m = 262.6 nm
This wavelength is not in visible range. It lies in Ultra Violet Region.
2. λ = 5.546 x 10⁻⁷ m = 554.6 nm
This wavelength is in visible range.
Explanation:
The binding energy of in photoelectric effect is also known as work function. The formula for this is given as follows:
Binding Energy = Work Function = hc/λ
λ = hc/Work Function --------------- equation (1)
where,
h = Plank's Constant = 6.626 x 10⁻³⁴ J.s
c = speed of light = 3 x 10⁸ m/s
λ = longest wavelength capable of ejecting electron = ?
(1)
Here,
Work Function = (4.73 eV)(1.6 x 10⁻¹⁹ J/1 eV) = 7.568 x 10⁻¹⁹ J
Therefore,
λ = (6.626 x 10⁻³⁴ J.s)(3 x 10⁸ m/s)/(7.568 x 10⁻¹⁹ J)
λ = 2.626 x 10⁻⁷ m = 262.6 nm
This wavelength is not in visible range. It lies in Ultra Violet Region.
(2)
Here,
Work Function = (2.24 eV)(1.6 x 10⁻¹⁹ J/1 eV) = 3.584 x 10⁻¹⁹ J
Therefore,
λ = (6.626 x 10⁻³⁴ J.s)(3 x 10⁸ m/s)/(3.584 x 10⁻¹⁹ J)
λ = 5.546 x 10⁻⁷ m = 554.6 nm
This wavelength is in visible range.
