 ### Photoelectric Effect 4

What is the effect of:
• Intensity (brightness, power)
• and Frequency
on the Photoelectric effect?

### INTENSITY (brightness, power)

The following diagram shows a dim light of frequency f being used to perform the photoelectric effect. Question:
What would happen if the light was made brighter, with the same frequency f?

There would be MORE electrons released since there would be more beams of light. But the kinetic energies of each electron would remain unchanged
It is important to note that if this was a solar cell, more current would flow due to the increased number of electrons, i.e. the brighter light increases the current strength due to the increase in the number of electrons.

In other words :
Brighter light:
• more photons
• produces more photoelectrons
• hence produces a greater current in a solar cell
• but does not increase the kinetic energies of each of the photoelectrons

### FREQUENCY

The following diagram shows a light of frequency f being used to perform the photoelectric effect. Question:
What would happen if the frequency was increased? (Not the intensity.) The photons would now have greater energy (140J). But since the work function of the metal is still the same, the kinetic energy of the photoelectrons would increase (60J).
(But the same number of electrons would be ejected since the photon was not made brighter.)

In other words:
Higher frequency light:
• increases the kinetic energy of each photoelectron
• would not change the number of electrons ejected, number of electrons remain the same
• more electrons ejected per second
• Some past papers state that there will an increase in current in the photocell. However other material say that the current would remain unchanged. This is because although the speed of the electrons have increased from where they have been ejected, the electron speed is unchanged inside the conductor! Hence current unchanged.