Question

An isolated copper sphere of radius 4.95 cm, initially uncharged, is illuminated by ultraviolet light of wavelength 251 nm. The work function for copper is 4.70 eV. What charge does the photoelectric effect induce on the sphere?

Answer 1

Answer:

the charge the photoelectric effect induce is 0.132 × 10⁻¹¹ C

Explanation:

energy of ultraviolet light  = $\dfrac{hc}{\lambda}$

                                           = $\dfrac{6.626 \times 10^{-34}\times 3 \times 10^8}{251\times 10^{-9}}$

                                           =7.91 × 10⁻¹⁹ J

                                           =4.94 e V  

energy released by the electron = 4.94 - 4.70

                                                      = 0.24 e V

potential at the surface of sphere =$\dfrac{K Q}{r}$

                                                 0.24 = $\dfrac{9\times 10^9\times Q}{0.0495}$

                                                    Q = 0.132 × 10⁻¹¹ C

hence, the charge the photoelectric effect induce is 0.132 × 10⁻¹¹ C