Photoelectric Effect

Photoelectric Effect

Evidence for the particle-like behavior of electromagnetic waves is provided by the Photoelectric Effect.

Electrons are released from the surface of a metal when it absorbs electromagnetic radiation in the photoelectric effect.

The following illustration illustrates this phenomenon.

Different metals have unique threshold frequencies, fo, below which no electrons are released electrons are released with varying kinetic energies up to a maximum of (½mv2)max when the frequency surpasses this threshold

The Photoelectric effect cannot be accounted for by the wave model.

The explanation for this phenomenon relies on the concept of a photon, which is a discrete unit of energy carried by EM radiation in short bursts.

The relationship between the frequency of a photon and its energy, denoted by E, is expressed as:

E = refers to the energy of a photon, measured in Joules (J)

h = denotes the Planck constant, equal to 6.63 x 10-34 Joule seconds (Js)

f = represents the frequency of the photon, measured in Hertz (Hz)

c = stands for the speed of light, equal to 3.00 x 108 meters per second (m/s)

λ= represents the wavelength of the photon, measured in meters (m)

The energy of a photon can be measured in Joules or Electronvolts (eV).

One electronvolt is equivalent to the energy transferred when an electron moves through a potential difference of 1 volt, given by: 1 eV = 1.60×10-19 J

The minimum energy required for an electron to escape a metal is called the work function, denoted by Φ

If the energy is less than Φ, no emission occurs

Emission can occur when hf = Φ

The photoelectric equation relates the maximum kinetic energy of the emitted electrons to the work function and the energy of each photon: hf = Φ + (½mv2)At the threshold frequency, the minimum frequency required to cause emission is zero, so the equation becomes: hfo = Φ

Introduction

An atom is composed of protons, neutrons, and electrons that orbit around the nucleus, as depicted in Figure 1. In certain metals, some electrons are not bound and are free to move. These free electrons are referred to as conduction electrons. Removing these electrons from a metal necessitates energy since they are retained in the metal by the electrostatic attraction of positively charged nuclei. To extract an electron from a metal surface, energy must be supplied. When this energy is in the form of light, the process is referred to as photoemission or the photoelectric effect

A. Photoelectric Effect

Photoemission refers to the liberation of electrons from a metal surface upon exposure to electromagnetic radiation. The electrons released in this process are referred to as photoelectrons. The energy level of photoelectrons can be investigated through an experiment depicted in Figure 2.

To conduct the experiment, ultraviolet radiation of varying frequencies can be employed. A graph depicting the relationship between the frequency of the radiation and the maximum kinetic energy of the emitted photoelectrons can be generated from the data collected:

B. Work Function Energy

The energy required for an electron to escape a source is known as the work function energy (Φ).

C. Threshold Frequency

Photoemission only occurs if the frequency of the incoming radiation exceeds a minimum value known as the threshold frequency (fo).

D. Einstein’s Theory of Photoelectric Emission

Max Planck, a German physicist, proposed that electromagnetic radiation could be comprised of distinct packets of energy known as quanta. The amount of energy (E) present in each quantum can be determined using the following equation:

E = hf

Where,

h – Plank constant (6.63 x 10^-34 J s)

f – Frequency of the radiation

Albert Einstein’s theory of quantized energy posits that light energy is composed of a series of energy packets called photons, which are quanta of energy that manifest as electromagnetic radiation. Einstein utilized the principle of energy conservation to derive the photoelectric equation.

E. Summary

• For an electron to escape from the surface of a metal, it must receive energy. If the energy is provided by light, then the process is referred to as photoelectric emission.
• Photoelectric emission is the process in which electrons are released from a metal’s surface upon exposure to electromagnetic radiation.
• Electrons released during photoelectric emission are known as photoelectrons.
• The minimum energy required for an electron to escape a metal’s surface is known as the work function energy (Ф).
• Photoelectric emission only occurs when the frequency of the incident radiation exceeds the threshold frequency (fo).
• The energy present in each quantum is referred to as the quantum energy, E = hf ( – Plank constant (6.63 x 10^-34 J s)
• A photon is a quantum of energy present in electromagnetic radiation.