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The photoelectric effect is a phenomenon in which electrons are ejected from the surface of a metal when light strikes it. These ejected electrons are called photoelectrons. It is important to note that the photoelectron emission and the kinetic energy of the ejected photoelectrons depend on the frequency of the light incident on the metal surface. The process by which photoelectrons are ejected from the metal surface due to exposure to light is commonly known as photoemission.
In this article, we will learn about Photoelectric Effect, Photoelectric effect equation, Photoelectric effect was discovered by and more.
Introduction
The photoelectric effect occurs because electrons on the metal surface tend to absorb energy from incident light, thereby overcoming the attractive forces that bind them to metal cores or metal nuclei.
The photoelectric effect is a phenomenon in which electrons are ejected from the surface of a metal when light strikes it.
Definition
The photoelectric effect is a phenomenon in which electrons are ejected from the surface of a metal when light strikes it. These ejected electrons are called photoelectrons.
History Of photoelectric effect
The photoelectric effect was discovered by Wilhelm Ludwig Franz Hallwachs in 1887 and experimentally verified by Heinrich Rudolf Hertz. They observed that when a surface is exposed to electromagnetic radiation with high threshold frequency, the radiation is absorbed and electrons are emitted. Today we study the photoelectric effect as a phenomenon in which a material absorbs electromagnetic radiation and releases electrically charged particles.
Threshold Energy for Photoelectric Effect
Photoelectric effect arises when the photons which are incident on the surface of metal must have to carry sufficient energy to overcome the attractive forces which bind the electrons to the nuclei of metals. The minimum amount of energy required to remove an electron from the metal is called the threshold energy (indicated by the symbol Φ). For a photon to have an energy equal to the threshold energy, its frequency must equal the threshold frequency (which is the minimum frequency of light required for the photoelectric effect to occur).
Einstein’s Equation of the Photoelectric Effect
According to the Einstein-Planck relationship, Einstein explained the photoelectric effect on the basis of Planck’s quantum theory, according to which light radiation propagates in the form of discrete photons.
The photoelectric effect equation which is given by Einstein is
E=h
Here,
E = Energy of photon
h = Planck’s constant
v= Frequency
From the experiments of the photoelectric effect, it is found that no electron emission occurs when the incident radiation has a frequency lower than the threshold frequency. From the equation you can see that energy is directly related to frequency and this also explains the instantaneous nature of the electron emissions.
When the photoelectron leaves the metal surface, it is converted into pure kinetic energy since there is no electric field in the exterior of the surface. The quantum energy which is transmitted by the photons is partly used by the electron to get rid of the molecular attraction of the surface.
Hence,
Kinetic energy = (Energy Imparted by photon) – (Energy used to come out of the surface).
This is the photoelectric effect equation which is given by Einstein.
Properties of the Photon
- For a photon, all quantum numbers are zero.
- A photon has no mass, no charge and is not reflected in a magnetic and electric field.
- The photon moves at the speed of light in empty space.
- When matter interacts with radiation, the radiation behaves as if it is made up of small particles called photons.
- Photons are virtual particles and their energy is directly proportional to the frequency and inversely proportional to the wavelength.
Threshold Frequency
It is the minimum frequency of the incident light or radiation that produces a photoelectric effect, i.e. H. the ejection of photoelectrons from a metal surface is known as the threshold frequency for the metal. It is constant for a given metal, but can be different for different metals.
Threshold Wavelength
During electron emission, a metallic surface that corresponds to the longest wavelength of the incident light is called the threshold wavelength.
{th}=c/v{th}
Here,
{th}= Threshold wavelength
c = velocity
v{th}= Threshold frequency
Work Function or Threshold Energy (Φ)
The minimum energy of thermodynamic work required to remove an electron from a conductor to a point in vacuum just outside the surface of the conductor is known as the threshold energy/work function.
=h{th}
=(hc)/{th}
Here,
= work function
{th}= Threshold wavelength
c= velocity
{th}= Threshold frequency
Characteristics Of Photoelectric Effect
- The threshold frequency varies with the material, it is different for different materials.
- The photocurrent is directly proportional to the light intensity.
- The kinetic energy of photoelectrons is directly proportional to the light frequency.
- The stopping/braking potential is directly proportional to the frequency and the process/action is instantaneous.
Conclusion
The photoelectric effect is a phenomenon in which electrons are ejected from the surface of a metal when light strikes it. These ejected electrons are called photoelectrons. It is important to note that the photoelectron emission and the kinetic energy of the ejected photoelectrons depend on the frequency of the light incident on the metal surface. The process by which photoelectrons are ejected from the metal surface due to exposure to light is commonly known as photoemission.
In this article, we learn about Photoelectric Effect, Photoelectric effect equation, photoelectric effect was discovered by and more.
The minimum energy of thermodynamic work required to remove an electron from a conductor to a point in vacuum just outside the surface of the conductor is known as the threshold energy/work function.
There are some applications of Photoelectric effect which are given below
- Photoelectric cells are used in burglar alarms.
- Photoelectric effect is used in photomultipliers to detect the low levels of light.
- Photoelectric effect was used in video camera tubes in the starting days of television.
Example
Brakes applied by bus driver suddenly
On a bus trip, when the bus driver suddenly presses the brake, we tend to feel a momentary push forward. The reason for this feeling by passengers sitting inside the bus is because of the law of inertia. Due to the inertia of motion, our body continues to maintain a state of motion even after the bus has stopped, thus pushing us forward.
Newton’s Second Law of Motion
Sir Isaac Newton’s First Law of Motion states, A frame at relaxation will continue to be at relaxation, and a frame in movement will be in movement until it’s far acted upon via any outer or external force. Then, what occurs to a frame while an outside force is carried out to it? That scenario is defined by Newton’s Second Law of Motion. According to NASA, this regulation states, Force is identical to the change in momentum in line with change in time. For a regular mass, force equals mass into acceleration. In mathematical form it is written as F = ma, where F equals force, m is mass of object and a is acceleration of object. The math at the back of that is pretty simple. If you double the force, you double the acceleration, however in case you double the mass, you narrow the acceleration in half. Because the acceleration is directly, and mass is inversely proportional.
Formula
According to Newton’s Second laws of motion
F = ma
Where, F = force, m = mass of the object, a = acceleration
Example
Hitting of a ball
A ball develops a certain acceleration after being hitted. The acceleration with which the ball moves is directly proportional to the force acting on it. This means the harder you will hit the ball, the faster it will move, proving Newton’s second law in everyday life.
Newton’s Third Law of Motion
According to Newton, whenever objects A and B interact, they exert force on each other. When you sit in the chair, your body exerts a downward force on the chair, and the chair exerts an upward force on your body. Here are two forces resulting from this interaction: a force on the chair and a force on your body. These two forces are called action force and reaction force and are the subject of Newton’s third law of motion. Basically it stated by Newton’s third law is: for every action, there is an equal and opposite reaction. The statement means that in every interaction there is a pair of forces acting on the two interacting objects. The size of the forces on the first object is equal to the size of the force on the second object. And the direction of the force on the first object is opposite to the direction of the force on the second object. Forces always occur in pairs of equal and opposite reaction-action forces.
Example
Stretching an elastic band
When someone pulls an elastic band, it returns to its authentic position automatically after leaving it. The more distance you pull it, it exerts the extra force. This is identical while you pull or compress a spring respectively. This pull action is stored as energy and is released as a reaction with the same and opposite force.
Conclusion
Newton’s give three important laws of motion that become the root of classical mechanics, it explains every aspect related to rest and motion of any object. Moreover it explains about the force acting on the object and it also explains that every object exerts forces on each other when they are in contact.
