Two metals X and Y have work functions 2.0 eV and 4.0 eV respectively. When illuminated by a monochromatic light source, it is observed that metal X emits photoelectrons while metal Y does not. Which of the following could be the wavelength of the incident light? (Take hc = 1240 eV nm )

Step-by-step solution

For photoelectric emission to occur, the incident wavelength must be less than the threshold wavelength _ th , where _ th = hc . For metal X : _ th, X = 1240 2.0 = 620 nm For metal Y : _ th, Y = 1240 4.0 = 310 nm Since metal X emits photoelectrons, the incident wavelength must be Since metal Y does not emit photoelectrons, the incident wavelength must be > 310 nm . Thus, the possible wavelength must lie in the range 310 nm Answer: 500 nm