Aray of yellow light has a wavelength of about 5.8×10−7 m. will exposure to yellow light cause electrons to be emitted from cesium?

Given the wavelength of the yellow light (700 nm. in this case) we can find the frequency 
by dividing the speed of light c by the wavelength w, that is: f = c/w and we know that 
c is equal to 2.998 * 10**8 meters per second. 
So the frequency f = (2.998 * 10**8) / (7.0 * 10**-7) = 4.283 * 10**14 cycles per sec. 
(or Hz.) Since the threshold frequency of Cs is 9.39 * 10**14 Hz, the red light doesn't 
have a high enough frequency (or energy) to cause electron emission. 
Hope this answers your question.