Question

A ray 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?

Answer 1

the wavelength of the red light = 700 nm
f = c/w
c =  2.998 * 10**8 meters per second. 

f = (2.998 * 10**8) / (7.0 * 10**-7) = 4.283 * 10**14 cycles per sec. 

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.