CHEMISTRY COMMUNITY

Higher frequency light always emits electrons with higher: kinetic energy or low kinetic energy?
Asking from Midterm Q3 D

Assuming that the frequency is already high enough for an electron to be ejected, higher frequency light would emit electrons with higher kinetic energy. However, for the midterm question, you can't make this assumption (and therefore the statement is not true).

Joshua Xian 1D wrote:Assuming that the frequency is already high enough for an electron to be ejected, higher frequency light would emit electrons with higher kinetic energy. However, for the midterm question, you can't make this assumption (and therefore the statement is not true).

I just wanted to flesh this out a little more, partly for my sake, but also for anyone who is also trying to grapple with this idea. So if the incoming light (which contains a bunch of small packets of energy called photons) has a high frequency, it will have higher relative frequency than light energy with a low frequency and, thus, a larger wavelength. Okay so if this light energy crosses the threshold energy value, an electron will be able to be removed from the surface. Since higher frequencies of light contain more energy than lower frequencies, the light with the higher frequencies will tend to pass a threshold more readily. However, even if light has a super high frequency, you can't be sure that an electron will/will not be removed unless you have the value for the threshold energy. If you pass that threshold energy and then some[i][/i], then you'll have remaining kinetic energy. So to have the most kinetic energy, you'd have to have light energy (expressed in the frequency) that far surpasses the threshold energy. Okay cool! Hopefully that's right.

Yes Garrett, your explanation is correct.

How do you solve this question in the Photoelectric Module? What exactly is the Work function?

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.
Answer the following three questions.
What is the kinetic energy of the ejected electron?

The work function is the amount of energy it takes to initially eject an electron from the metal. This varies based on the metal. Light of insufficient energy, meaning less energy than the value of the work function, will not eject an electron. Light that has more energy than the work function uses some of the energy to overcome the work function, and the remainder of the energy becomes the electron's kinetic energy.

Keeping this in mind, use this concept and the equation E=hv to find the answer. Feel free to ask more questions if you need further help!