What is the photoelectric effect? Write down an expression for Einstein's photoelectric law - Leaving Cert Physics - Question 12(d) - 2005

Einstein's photoelectric law can be expressed as: $E = hf - ext{W}$ where:

• $E$ is the energy of the emitted electron,
• $h$ is Planck's constant,
• $f$ is the frequency of the incident light,
• $ext{W}$ is the work function of the metal.

Einstein's explanation of the photoelectric effect emphasizes that light is made up of photons, which are packets or quanta of energy. When a photon strikes the surface of a metal, it can transfer its entire energy to an electron. This energy transfer only results in the emission of the electron if the energy of the photon exceeds the work function of the metal. The work function is the minimum energy required for an electron to escape the surface. Thus, for the photoelectric effect to occur, the energy provided by the incoming photon must be greater than the work function of the metal.

One application of the photoelectric effect is in photoelectric sensors, such as those used in burglar alarms. These sensors detect changes in light levels, which can trigger an alarm if an intruder breaks a light beam.