I Want To Observe Photoelectric Effect

When light of wavelength $\lambda$ is incident on a sheet of metal, energy is transferred from the photons in the light, to the electrons in the metal. The emitted electron have a wide range of kinetic energies, ranging from $0$ to $\text{KE}_{\text{max}}$ . We can obtain $\text{KE}_{\text{max}}$ using the following formula:

$\frac{hc}{\lambda} = \frac{hc}{\lambda_0} + \text{KE}_{\text{max}}$

Each photon that strikes the metal has energy $\frac{hc}{\lambda}$ . Some amount of energy, $\frac{hc}{\lambda_0}$ is required to remove the electron from the surface of the metal. The rest of the energy is transferred to the electron as kinetic energy. Photoelectric effect is observed only when the most energetiv electrons have positive kinetic energy.

For $\text{KE}_{\text{max}}$ to positive, we see $\lambda$ must be less than $\lambda_0$ , also known as the threshold wavelength. The reason we did not observe photoelectric effect initially is because the wavelength of the incident light was greater than the threshold wavelength. If we decrease the wavelength of incident light, we may provide enough energy to the electrons to escape the metal and as a result we may observe photoelectric effect. $_\square$

Adjusting the brightness of light, or changing the distance of the lamp from the metal only changes the intensity of light incident on metal. Note that the intensity of incident light does not determine whether or not photoelectric effect is observed.

When light of a certain frequency falls on a metal, electrons tend to be emitted. But these electrons are acted upon by attractive forces of the metal, and have to perform a certain amount of work to overthese forces. This is known as the work function of the metal. The only condition for photo-electric emission is energy of these incident photon being greater than the work function. This energy can be increased by decreasing the wavelength ( increasing frequency ).

Increasing the brightness or taking lamp closer to metal sheet do no effect photoelectric effect(P.E.E.) . As P.E.E. Is independent of intensity of light.

Decreasing the wavelength will most likely result because then the frequency will be higher and the energy of the emitted light may exceed the work function.

This is the phenomenon that encouraged Albert Einstein to write the paper that resulted in his 1921 Nobel, which he was awarded in 1922 for his work on the phtoelectric effect in 1905.

The Nobel Prize in Physics 1921 was awarded to Albert Einstein "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."

Albert Einstein received his Nobel Prize one year later, in 1922. During the selection process in 1921, the Nobel Committee for Physics decided that none of the year's nominations met the criteria as outlined in the will of Alfred Nobel. According to the Nobel Foundation's statutes, the Nobel Prize can in such a case be reserved until the following year, and this statute was then applied. Albert Einstein therefore received his Nobel Prize for 1921 one year later, in 1922.

The Nobel Prize in Physics 1921. NobelPrize.org. Nobel Media AB 2019. Sun. 17 Feb 2019. <https://www.nobelprize.org/prizes/physics/1921/summary/>

"Instead, electrons are dislodged only by the impingement of photons when those photons reach or exceed a threshold frequency (energy). Below that threshold, no electrons are emitted from the material regardless of the light intensity or the length of time of exposure to the light. (Rarely, an electron will escape by absorbing two or more quanta. However, this is extremely rare because by the time it absorbs enough quanta to escape, the electron will probably have emitted the rest of the quanta.) To make sense of the fact that light can eject electrons even if its intensity is low, Albert Einstein proposed that a beam of light is not a wave propagating through space, but rather a collection of discrete wave packets (photons), each with energy hν. This shed light on Max Planck's previous discovery of the Planck relation (E = hν) linking energy (E) and frequency (ν) as arising from quantization of energy. The factor h is known as the Planck constant."