Question

Explain with the help of Einstein's photo electric equation any two observed features in photoelectric effect which cannot be explained by wave theory.??​

Answer 1

Answer:

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Explanation:

These are the two features of Photoelectric effect which can not be explained by wave theory but can be explained through Einstien's photoelectric equation:

1. For a given metal and a given frequency of incident radiation, the number of photoelectrons ejected per second is directly proportional to the intensity of the incident light.

2. For a given metal, there exists a certain minimum frequency of the incident radiation below which no emission of photoelectrons takes place. This frequency is called the threshold frequency.

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Answer 2

Answer:

• According to the photon concept, energy is present in light waves in the form of quanta, or energy packets. A photon is equivalent to a single quantum.
• According to Einstein's theory of photoelectric emission, if one photon of the right kind of light radiation strikes a metal surface, it will emit one photoelectron.
• Therefore, if a photon of light frequency, ν, strikes a surface of a photosensitive metal, its energy can be used in one of two ways: 

1. In releasing an electron from a metal surface whose work function Φ₀ is equal to that of the metal.
2. By providing kinetic energy to the photoelectrons that are released. Thus,

              hν = 1/2 mv² + Φ .......(i)

              1/2 mv² = hν - Φ .......(ii)

Where, v ⇒ velocity of emitted photo electron

m ⇒ mass of the photo electron.

Here, Eq. (2) is referred to as Einstein's photoelectric equation.

The two observed characteristics of the photoelectric effect that wave theory cannot account for are as follows:

1. According to the photoelectric theory, photoelectrons are emitted immediately after light strikes the metal. However, according to wave theory, the energy of the light wave does not go to a specific metal electron, but is instead spread to all of the electrons present in the illuminated section. As a result, it will take some time for the electrons to accumulate the energy needed for emission.
2. According to the photoelectric theory, regardless of intensity, the photoelectric effect does not occur if the frequency of the incident light is below the threshold frequency. However, according to wave theory, photoelectric emission from a metal surface is possible by light waves of any frequency as long as the intensity of the light is high enough to give electrons the necessary energy for their emission.

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