Textbook Problem 1B.15

[Katie Shi 1F]

Could anyone help explain part c? Why can we not just use the E from part b with the equation e = hc/lambda?

[Tanvi Akula 2K]

The energy from part b is just the work function. This is how much energy it takes to remove the electron. For part c, we want to find the wavelength of the radiation that caused the electron to eject. This means that we want to find the wavelength of the light energy. So light energy = work function + kinetic energy. So we use the work function from part b, and then calculate the KE using the velocity given in the beginning of the problem. So once we find the light energy, that's when we can plug it into e = hc/lambda to find the wavelength of the radiation.