All The Terms of Photoelectric Effect For Quick Reference

When electromagnetic radiation is absorbed by a material, electronically-charged particles are released from the material (or even within itself). This phenomenon is called the photoelectric effect.

The photoelectric effect was discovered by German physicist Heinrich Rudolf Hertz in 1887.

In this article, we have compiled all the terms of photoelectric effect for your easy and quick reference.

Kinetic energy

Kinetic energy is defined as the energy that a body possesses due to it being in motion.

The movement of the electrons or electric charges causes electrical energy. The electrical energy produced is directly proportional to the speed of the electrons. Electrical energy is said to be a form of kinetic energy because it is caused by the movement of electrons.

Frequency

Frequency is the number of waves that pass through a fixed point in a certain amount of time. So, in case the time taken for a wave to pass a point is 1/50th of an hour, then the frequency is 50 per hour.

Current

Current or electric current is the flow of electrons or electron-deficient atoms (collectively referred to as electrical charge carriers). Current is inversely proportional to resistance and directly proportional to voltage. 

Electric potential

The electric potential is defined as the amount of work required to be done to move a single unit of charge from a reference point (say ‘A’) to a specific point (say ‘B’) against the resistance of an electric field.

The difference in electric potential between two points is defined as the voltage. Its standard SI unit is Volt.

Conservation of momentum

Conservation means something that doesn’t change. Hence, conservation of momentum implies that if two or more bodies interact with each other in an isolated system (that is, no external force is acting upon them), then the total momentum of all the bodies remains constant.

Terms of the photoelectric effect

Having refreshed key concepts, let us now look at all the associated terms of the photoelectric effect.

Photoelectric effect or Photoemission or Photoelectric Emission

Under specific circumstances, electrons can be emitted out of the surface of a solid, when light strikes it. This is called the Photoelectric effect. It is also referred to as Photoemission or Photoelectric Emission.

Internal Photoemission

When the photoexcited electron or the photoelectron is emitted from one material to another, then the photoemission process is often referred to as Internal Photoemission.

External Photoemission

When the photoelectron is emitted from a material to a vacuum, then the photoemission process is referred to as External Photoemission.

Photoelectrons

The electrons which are emitted from a metal surface upon the influence of light are called photoelectrons. However, it is to be noted that these photoelectrons are not different in property from the electrons that remain behind in the metal. 

Photoemissive Material

The material that can exhibit the phenomenon of the photoelectric effect (that is, it is capable of emitting electrons when light strikes its surface) is said to be photoemissive material.

Binding Energy

In an atom, the negatively-charged electrons are held tightly together by the powerful electrostatic pull created by the positive charge of the nucleus. Thus, the binding energy of an electron is the smallest amount of energy required for an electron to overcome this force of attraction and break free from the atom. It is measured in electron volt (eV).

1eV = 1.6 x 10-19 J

Photon or Light Quantum

Light is said to consist of corpuscles or particles called photons. These photons, also sometimes referred to as light quantum, are small energy packets of electromagnetic radiation. Each photon contains a definite amount of energy called quantum. A photon has energy and movement. However, it is massless and does not have any electrical charge.

Threshold energy or Work function

Threshold energy is the minimum amount of energy needed by the electron to break free from the metal and eject from it.

Threshold frequency

The energy contained by a photon of light depends upon the frequency of the light. Thus, threshold frequency is the lowest frequency of electromagnetic radiation that will produce a photoelectric effect in a material. 

If light having a lower frequency than the threshold frequency were to fall on the material, then photoemission will not occur.

Threshold wavelength

The Threshold wavelength is the largest possible wavelength of the incident radiation which allows photoemission to take place. No photoemission occurs if the wavelength is higher than the threshold.

Saturated current

During photoemission experiments, if the intensity and frequency of the incident light or radiation are kept fixed, the photoelectric current will increase with an increase in the positive voltage (applied externally). However, beyond a certain voltage level, no incremental photoelectrons can flow. In such a situation, the photoelectric current is said to have reached a saturation value and this is called saturated current.

Stopping potential or Cut off potential

In the photoelectric experiments (refer to ‘Saturated current’), if the external voltage applied is negative, the flow of electrons is hindered. As the negative voltage is increased, the current becomes weaker due to lesser electrons flowing across. At a certain voltage level, the electrons completely stop moving and the current stops flowing. This voltage difference that’s required to stop the electrons from moving between the plates and generating a current in a photoelectric experiment is called the stopping potential or the cut-off potential.

Conclusion

In this lesson, we learned about the various terms of the photoelectric effect, how photoemission is caused and its application in our daily lives. When electromagnetic radiation is absorbed by a material, electronically-charged particles are released from the material. This phenomenon is called the photoelectric effect. Most common terms of photoelectric effects are threshold frequency, work function, kinetic energy of photoelectron, stopping potential, saturated current, photoelectron, etc.