When ultraviolet light with a wavelength of 254 nm falls on a clean copper surface, the stopping potential necessary to stop emission of photoelectrons is 0.181 v. part a what is the photoelectric threshold wavelength for this copper surface?

The ultraviolet wavelength λ = 254nm the stopping potential of copper surface,
V₀ = 0.18W
Now the relation  between threshold wavelength and stopping potential is
eV₀ = λc (1/λ - 1/λ₀)
1/λ - 1/λ₀ = eV₀/λc
1/λ₀ = 1/λ eV/λc
= 1/ 254 × 10⁻⁹m - 1.6 10⁻¹⁹C)(0.181v)/6.625 × 10⁻³⁴ Js (3×10⁸m/s
0.00393 × 10⁹ - 0.01457×10⁷
= 0.378 ×10⁷
λ₀ = 264 × 10⁻⁹m or
264nm 

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