Feb 7, 2010
How do i know the difference between when the intensity of the irradiating light increases and the energy of the irradiating light increases.

If work function is

KE= hf -(Workfunction)

then acc to a TPR question, increasing the intensity of light apparently increases the number of electrons ejected but not the kinetic energy of the electrons.

Increasing the energy of the photon increases the KE with which the electron ejected.

My question is, what quantity is intensity referring to?


turning mountains into molehills
7+ Year Member
Aug 18, 2011
Medical Student
Assuming it's just a conceptual question, the intensity of the light is referring to the amount of light (photons) striking a surface. As in, one light source shining on an object versus 10 light sources. Increasing the intensity of light increases the number of photons, which cause more electrons to be ejected, but since they are all the same wavelength, they all have the same energy thus it won't chance the ejected electron's kinetic energy.

But if you take the one light source, and change the energy of the light (by changing the wavelength) then it will change the kinetic energy of the electrons that are ejected.

Think of the light as a source of photons, which strike electrons in a 1-to-1 ratio. Increasing the number of photons doesn't make the electrons get ejected any faster, it just causes more to be ejected.

I hope that was helpful and not confusing.
Aug 12, 2013
Medical Student
As jayoh stated, but a little more condensed:

intensity = related to the number of photons that strike the surface, but not their energies
frequency = related to the energy of each photon that strikes the surface (E=hf)