Category: Physics Notes PPT

Motional emf is a process in which an emf is inserted into a conductor as a result of its movement within a magnetic field. Suppose a U-shaped spinning wire is inserted into the magnetic field and a metal rod is placed over the wire. If a metal conducting rod is allowed to go right or left with a U-shaped wire, the emf will be inserted inside that loop. This inserted emf is commonly referred to as motional emf. Many applications of this concept exist, as we will see in the next article (electric blood flow meter).

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To understand electromotive electromagnetic force, let’s do something. Let’s take a rectangular coil, an L-shaped steel rod, traveling V-speed, passing through magnetic field B. There is a magnetic field somewhere.

Length, speed and magnetic field must always be at right angles to each other. The direction of the magnetic field goes inward. Assume that the steel rod is not rigid which means there is no loss of strength due to sliding and we use the same magnetic field. The conductor rod is moved at a constant speed and placed in a magnetic field.

But ‘x’ changes over time,

E = -[frac{dPhi }{Bdt} = -frac{d}{dt} = -left ( Blx right ) = -Blfrac{dx}{dt}]

E = Blv

The inserted emf Blv is a dynamic electromotive force. We therefore produce the emf by moving the conductor within the same magnetic field. The force required to move the conductor rod into the magnetic field,

P = [frac{B^{2}l^{2}v^{2}}{R}]

There,

B is a magnetic field,

l conductor length

v driver speed

R resistance

The magnetic flux associated with the coil is given by Φ = BA cos θ. We know that cos θ = 0, so Φ = BA. The electromotive power movement can also be described as the Lorentz power that works on free carriers. Lorentz’s strengths are in control:

F = qVB

EMF

Any change in magnetic flux induces an emf opposing that change is the process known as induction. The motion is one of the major causes of the process of induction. For example, we can say that a magnet which has moved toward a coil induces an emf and a coil which has moved toward a magnet produces a similar emf. In this section, we will discuss motion in a magnetic field stationary relative to the planet Earth producing what is loosely known as motional emf. There is one situation where we can say there is a motion that generally occurs, called the Hall effect and has already been examined. The moving charges which are moving in a magnetic field experience the magnetic force denoted by F = qvB. Refer to the official website of or download the app for an elaborate and comprehensive explanation. 

What is Motional EMF?

The charge which we are talking about in opposite directions and produces an emf = Bℓv. We can generally see that the Hall effect has applications which include measurements that are of symbols which are B and v. We will also notice now that the Hall effect is one aspect of the broader phenomenon of induction and we will conclude that motional emf can be used as a power source. Here we should consider the situation of a rod moving at a speed v along a pair of conducting rails which are separated by a distance denoted by symbol ℓ in a uniform magnetic field B. The rails which are stationary relative to B and are connected to a stationary resistor denoted by R.

 

Motional Electro-Motive Force

The resistor generally could be anything from a light bulb to even a voltmeter. Let us consider the area enclosed by the moving rod, rails, and resistor. The letter B which we know is perpendicular to this area and we can say that the area is increasing as the rod moves. Thus, here we notice that the magnetic flux generally enclosed by the rails and the rod and resistor is increasing. When the term changes then generally an emf is induced according to Faraday’s law of induction.

Here again, we see that to find the magnitude of emf induced along the moving rod uses the law of Faraday of induction without the sign:

denoted as emf = [frac{NDelta }{Phi Delta }]

Here and below also the term “emf” is the magnitude of the emf. In this equation we have learnt that the equation N = 1 and the flux denoted by Φ = BA cos θ. We have already seen a symbol denoted by letter or symbol θ = 0º and cos θ = 1 since B is perpendicular to A. Now the symbol ∆Φ = ∆(BA) = BΔA since B is uniform. We can see that the area swept out by the rod is ∆A = l∆x. 

Lenz’s Law

Lenz’s law of electromagnetic input states that the current induced magnetic field current (according to Faraday’s magnetic field) is so precise that the current induced magnetic field contradicts the original magnetic field that it produced. . Guidance for this current flow is provided by Fleming’s right-handed law.

Lenz’s law is based on Faraday’s import law. Faraday’s law tells us that a flexible magnetic field will apply current to a conductor.

Lenz’s law tells us the direction of what is currently being done, which contradicts the first ever-changing magnetic field it has produced. This is indicated in the Faraday law formula with the negative symbol (‘-’).

E = -[frac{dPhi _{b}}{Bdt}]

To find the direction of the induced field, the direction of the current and the polarity of the induced emf we apply the law of Lenz’s The term Flux is increasing too since the area enclosed is increasing. Motional emf also occurs if the magnetic field that moves and the rod or other object is stationary relative to the planet Earth or we can say some observer. We have also seen an example of this in the situation where a moving magnet induces an emf in a stationary coil. It is the relative motion that is important. What is emerging in these observations that we have already seen is a connection between magnetic and electric fields. A moving magnetic field generally produces an electric field seen through its induced emf. We already have seen in our article a moving electric field which generally produces a magnetic field moving charge that generally implies moving electric field and moving charge which produces a magnetic field.

Calculating Motional Electro-Motive Force

The emf of earth’s weak field magnetic is not ordinarily very large or we would notice voltage that along the rod of metal such as a screwdriver during ordinary motions. For example, we can say that a simple calculation of the motional emf of a 1 m rod that is moving at 3.0 m/s perpendicular to the planets earth’s field gives emf = Bℓv = (5.0 × 10⁻⁵ T)(1.0 m)(3.0 m/s) = 150 μV. 

We can say that there is a spectacular exception, however. In 1996 and 1992 attempts were made with the space shuttle to create large motions that have EMFs. A tethered Satellite which was to be let out on a length of 20 km of wire to create a 5 kV emf by moving at a speed orbital through the field of the planet Earth’s. To complete the circuit the stationary ionosphere was to supply a return path for the current to flow. The ionosphere is rarefied and we can say it is the partially ionized atmosphere at orbital altitudes. It could be said to conduct because of the ionization. The ionosphere that generally serves the same function as the stationary rails and the connecting resistor without which there would not be a complete circuit.

 

Concept Explanation

This concept of moving emf can be explained with the help of the Lo
rentz force concept that works on driver-free carriers. Let us consider any incorrect charge on the PQ conductor. As the rod moves at a constant speed v, the charging also travels at a constant speed v in front of the magnetic field B. Lorentz’s power in this charge is given:

F = qvB

The work done to move the charge from P to Q can be provided by,

W = QBvl

As, emf is defined as the function performed per unit,

∈ = wq = Bvl

A neutron is a subatomic particle holding no charge. This particle was discovered by James Chadwick in 1932 where he observed that when beryllium was bombarded with the alpha particles neutral radiation was emitted. The application of principles of conservation of energy and momentum stated that the bombardment of beryllium with alpha particles led to extremely penetrating radiations that could not be deflected by an electrical or magnetic field were not protons. They were neutrons because neutrons are chargeless particles, and do not get deflected by an electric or magnetic field.

 

Moreover, after the discovery of the neutron by James Chadwick, the English physicist, several investigators in the entire world began to study the interactions and properties of the particle. Besides, it was also discovered that when elements are bombarded by neutrons, they undergo fission which is a nuclear reaction that happens when the nucleus of any heavy element splits into two equal but smaller fragments.

 

In the year 1942, under the leadership and guidance of physicist Enrico Fermi, a group of researchers showed that to sustain a chain reaction, free neutrons are made during the fission process. This major development led to the formation of the atomic bomb. Nevertheless, neutrons have become an important instrument for pure research purposes.

 

 

The Neutrons Have Slightly Higher Mass than the Protons Given by,

 

Isodiaphers 

In nuclear physics, isodiaphers refer to the set of elements having different numbers of protons (atomic number) and neutrons and mass number (no of neutrons + no of protons) however they have the same difference between the number of neutrons and protons and neutrons excess are same.

To determine if the atoms are isodiaphers, we use the formula,

 

Where P is the number of protons and N is the number of neutrons that can be calculated by the difference in mass number (A) of an atom and the number of protons in that atom. 

If the difference of N- P in each atom comes out to be the same, then those two atoms are considered as isodiaphers.

 

Isobars and Isotones

Isobars

The set of elements has the same number of nucleons, where nucleons are protons or neutrons. For example, 40 Sulfur, 40 Chlorine, 40 Argon, 40 Potassium, and 40 Calcium are all isobars. Moreover, despite having the same mass number, isobars have different atomic numbers for different chemical elements. While stable isotopes can exist in a free state, radioactive isotopes are way too unstable to even sustain. Besides, in 1918, Alfred Walter Stewart, recommended the word isobar while it is derived from the word isos, which means equal, and baros, which means weight in the Greek language.

 

Isotones

The two or more atoms or nuclei having the same number of neutrons are called isotones. For example, 36S, 37Cl, 38Ar, 39K and 40 Ca nuclei are isotones as they all comprise 20 neutrons. 

 

Isotones Examples

Example 1

Chlorine-37 and Potassium-39

Chlorine (Cl)

No of protons  = 17

No of neutrons = 37 – 17 = 20

Potassium (K)

No of protons = 19

No of neutrons = 39- 19 = 20

Cl and K are isotones

 

Example 2

32 Ge 76 and 34 Se 78

Germanium (Ge)

No of neutrons = 76 – 32 = 44

Selenium (Se) 

No of neutrons = 78 – 34 = 44

Ge and Se are isotones.

 

Isodiaphers Examples

The atoms of different elements have the same difference of neutrons and protons.

Example1

Thorium – 234  =  90 Th 144

No of protons (atomic number Z ) = 90

Since mass number = no of neutrons + no of protons

Mass number (denoted by A) = 234 and no of protons = 90

No of neutrons = 234 – 90 = 144

Difference between neutrons and protons  = 144 -90 = 54…(1)

and Uranium-238  =  92 U 238

No of protons (atomic number Z)  = 92

No of neutrons = 146

Difference between neutrons and protons  = 146 – 92 = 54….(2)

As you can see in eq(1) and eq(2) the difference between the neutrons and protons for Thorium-234 and Uranium-238 are the same. Hence we can say that these two elements are isodiaphers.

 

Example 2

9 F 19 and Sodium 11 Na 23

Fluorine  

No of protons = 9 

and number of neutrons = 10 (19 – 9)

Difference  = 10 -9 = 1

Sodium 

No of protons = 11  and

number of neutrons = 12 (23 – 11)

So the difference will be  = 12  – 11  = 1

Here, we can see that the difference is the same, i.e. 1.

Hence fluorine and sodium are isodiaphers.

 

Isomer and Isotope

Isomer

Isomer is a Greek word, which means having equal share or part.

In nuclear physics, any two or more nuclei that possess the same number of neutrons and protons and mass number, however, exist in different energy states and have different radioactive properties.

It can also be said that the nuclei exist in any of several energy states for a measurable period of time.

For example, two nuclear isomers of Cobalt-58 are 58Co and 58mCo

Where 58Co  is a lower energy isomer has a half-life of 71 days and the high energy isomer is 58mCo (here m is for metastable which means 58mCo tends to remain in the state of equilibrium) having a half-life of 9 hours undergoes gamma decay further to form 58Co.

 

Gamma Decay

It is the stage that occurs when a nucleus is in an excited state and has too much energy to be stable, only energy is emitted however the number of protons remains the same.

 

Half-life 

In radioactive decay, the half-life is the duration of time following which there is a 50% chance that the atom will undergo nuclear decay.

 

Isotope

Isotopes are the set of atoms or nuclei that have the same number of protons however different numbers of neutrons. For example, Carbon-12 and Carbon-14 have 6 protons in each, however, have 6 and 8 neutrons respectively.

 

Nevertheless, you may have never noticed but in the periodic table, each square on it represents a family none other than isotopes, in which atoms have different masses but share the same chemical properties and name. In order to understand and go in-depth to know what isotopes can be used for, one must take a peek into the interior of an atom. Besides, in nature, there are around three isotopes of carbon consisting of carbon-12, carbon-14
, and carbon-13 while all these three carbons have six protons but their neutron numbers differ. All these three are chemically indistinguishable as in each of three isotopes, the number of electrons remains the same. So if we speak chemically, different isotopes of the very same element remain identical. But if the isotope transforms into another element then the ability of this rule changes.

The process in which the nuclei of two light atoms combine to form a new nucleus is known as nuclear fusion. It is the process that powers the sun and the stars and is the ultimate energy source for the future of mankind as it is another way of producing nuclear energy like nuclear fission.

The combination of Deuterium and Tritium, the two isotopes of Hydrogen to give Helium and releasing a neutron and giving out around 17 MeV of energy is an example of a nuclear fusion.

Nuclear Fusion reactions occur when two or more nuclei of the atom come close enough up to the extent that the nuclear force pulling them together exceeds the electrostatic force that pushes them apart, fusing them into heavier nuclei. For nuclei lighter than iron-56 the reaction is exothermic, thus releasing energy while for nuclei heavier than iron-56, the reaction is endothermic, thus requiring energy. 

Therefore we can say that nuclei smaller than iron-56 are more likely to fuse while those heavier than iron-56 are more likely to break apart.

Nuclear Binding Energy and Nuclear Fusion

When two lighter nuclei undergo a fusion reaction, the combination has a mass that is less than the mass of the initial individual nuclei. This difference in the mass between the reactants and products is compensated by either the release or absorption of energy known as binding energy between the atomic nuclei before and after the reaction. 

Einstein’s mass-energy equivalence explains the energy that the reaction gives out energy during Fusion.

Applications of Nuclear Fusion

One of the main uses of nuclear fusion is that of generating electricity. Fusion power makes use of heat that is generated from nuclear fusion reactions to produce electricity with the help of a device called a thermonuclear reactor. In this process, two atomic nuclei that are considerably lighter, are combined to form a heavier nuclear, while releasing energy. 

It is a very safe, environmentally friendly, and clean source of energy that creates way less waste than the process of nuclear fission does. 

Types of Fusion Reactors 

There are several approaches to control and contain a fusion reaction to exist, but the two primary approaches based on confinement are the concept of magnetic confinement and inertial confinement.

Magnetic confinement fusion (MCF) reactors are the more advanced of the two approaches, as and in this they utilise magnetic fields generated by electromagnetic coils to confine a fusion plasma in a donut-shaped (torus) vessel.

Unlike magnetic confinement approaches, inertial confinement fusion (ICF) approaches attempt to externally heat and compress fusion fuel targets to achieve the very high temperatures and even higher densities required to initiate nuclear fusion. 

For most ICF concepts and approaches, high power lasers are used to compress and heat the fuel.

Recently, a third approach, which exploits the parameter space between the conditions produced and needed for magnetic and inertial confinement has gained traction in recent years and is receiving much scientific, and even commercial, attention. This is called Magnetised target fusion (MTF), sometimes known as magnetized inertial fusion (MIF), it looks to exploit the use of higher density plasmas than for MCF approaches, but lower power lasers and other drivers than those used in ICF approaches. MTF offers a unique route to fusion, and the accelerated development of several unique concepts has seen significant support.

Components of Magnetic Confinement Reactors

• Vacuum vessels are used to hold the plasma and to keep the reaction chamber in a vacuum.

• A neutral beam injector is used to inject particle beams from the accelerator into the plasma thus heating the plasma to its critical temperature.

• Magnetic field coils are used in magnetic fields, and the plasma is confined in the superconducting magnets.

• A central solenoid is used to provide electricity to the magnetic field coils.

• Cooling equipment is used to cool down the magnets.

• Blanket modules: These are generally used to absorb heat and high-energy neutrons from the fusion reaction.

• Diverters: They are used to exhaust helium products.

Advantages of Nuclear Fusion

Fusion is capable of powering the whole world at a very low cost since there is virtually limitless fuel available that can be used to make electricity. There is a lot of energy released in fusion rather than fission, therefore it would be more profitable if it is set up. Also when producing nuclear fusion energy, there is hardly any waste. As a result of this, there would be no money wasted in disposing and clearing of the wastes produced by the reaction.

Thus, Fusion is capable of powering the entire world at a much low cost, as compared to power sources used nowadays. It is a clean energy source that means no greenhouse gases and emitting only helium as exhaust. It is easier to stop nuclear fusion reactions as compared to fission reactions since there is no chain reaction in fusion.

Disadvantages of Nuclear Fusion

It would be very expensive to build a power plant to produce energy because Nuclear fusion can only occur between 14999726.85 degree celsius to 9999726.85 degree Celsius. (Or 10-15 million kelvin) Thus, there are no materials that can cope with 10-15 million K and also since it is a non-renewable energy. There can also be radioactive wastes.

Interesting Facts about Nuclear Energy

Nuclear energy is derived from uranium which is a non-renewable resource that we get from mining. 

In the 1930s, a scientist named Hans Bethe discovered the possibility of nuclear fusion and how it was an energy source for the sun. 

The energy generated from the process of nuclear fusion is abundant in supply, limitless even. 

The largest successful nuclear reactor is at the Culham Science Centre in Oxford. 

This article contains an explanation of the orthorhombic system, examples, and some solved examples. If you incur any doubts while reading the article you can refer to the frequently asked questions at the end.

In the study of crystals, there are classifications based on the basic geometry of the crystal. Scientists named these groups the primitive crystal systems. The orthorhombic crystal system is one of the categories into which we can classify our crystalline solids. The names of all the seven crystal systems are as follows: cubic, tetragonal, orthorhombic, hexagonal, triclinic, monoclinic, and rhombohedral. These systems work on the principle of the three axes on which we draw the crystals and the relation of the axes to each other. This article lays focus on the orthorhombic structure. 

Orthorhombic Crystal

In this category of crystal systems, we can place the crystal on three mutually perpendicular axes which are of unequal length. This property is the defining characteristic of this group. The orthorhombic crystal system has its own set of unit cells. To understand what a unit cell is, one must imagine the atoms or atom groups in the crystal structure as points. If we join these points, we obtain a structure known as the lattice. If we observe, this lattice consists of stacks of blocks, and these we call unit cells. 

 

The orthorhombic is a three-axis System each of which are mutually at 90° angles and x axis is vertical and the shortest with the a axis which is intermediate in length and is from front to back and the B axis is taken as left to right with the longest.

Orthorhombic Unit Cell

The orthorhombic unit cell has its own set of unique characteristics. This unit cell has a set of three axes which we call the axes of twofold symmetry. If we rotate the crystal about these lines by an angle of 180°, the crystal will not change its appearance. To fulfill this property, the unit cell must have certain defined characteristics. In an orthorhombic unit cell, the angle between any two edges is always 90°. The edge lengths can, however, be unequal. 

 

Examples of Orthorhombic Structure 

Some examples of crystalline solids which take up the orthorhombic structure are as follows:

• enargite 

• marcasite 

• cerussite 

• barite 

• staurolite

• topaz

• orthoenstatite 

• aragonite 

• olivine 

• cementite 

• alpha-sulfur 

 

 

Variants of the Orthorhombic Crystal System

The orthorhombic system undergoes further classification to give rise to three subgroups of crystals. The common characteristic of these subgroups is that they consist of three mutually perpendicular axes which are unequal in length. These types are named the body-centred orthorhombic crystal system, base-centred orthorhombic crystal system, and face-centred orthorhombic crystal system respectively. The definitions of each of these crystal systems are as below: 

• Body-Centred Orthorhombic Crystal System: In this type of crystal structure, the lattice point is in the middle of the unit cell. 

• Base-Centred Orthorhombic Crystal System: In this type of crystal structure, there is a lattice point in the middle of each of the two ends. 

• Face-Centred Orthorhombic Crystal System: In this type of crystal structure, there exists a lattice point in the middle of each side. 

Solved Examples 

1. Define an Orthorhombic Crystal. 

Answer: Orthorhombic system is one of the structural categories of crystals systems into which we can classify crystalline solids. In this type of crystal structure, the lattice consists of three axes that are perpendicular to each other and whose lengths may or may not be inconsistent. 

 

2. State Whether this Statement is True or Not: In the Orthorhombic Crystal System, All Axial Angles are of the Same Value and are Identical. 

Answer: The statement is correct. The orthorhombic structure is such that all the crystallographic angles are of the same measure. This property is a fundamental characteristic of this type of crystal. 

 

3. State How a Crystal Structure and a Crystal System are Different Terminologies.

Answer: When we talk about a crystal structure, we mean the arrangement of atoms and the geometry which exists within the unit cell of the crystal. However, when talking of crystal systems, only the unit cell geometry comes into consideration. For example, body-centred and face-centred are crystal structures that fall under the orthorhombic crystal system.

 

4. Why is it So Essential to Know about Crystal Systems?

Answer: The importance of our awareness of crystal systems and crystal structures becomes clear when we obtain crystalline solids for use in our daily life. Two crystals having different structures will exhibit very different physical characteristics. The finest example of this is graphite and diamond. Due to their separate crystal systems and structures, one of these solids is exceptionally hard while the other is soft. These properties define their application, and thus, knowing how these crystals will behave under different physical conditions is essential.

 

5. What is orthorhombic and monoclinic?

Answer. Monoclinic is (crystallography) has three unequal axes with two perpendiculars and one oblique intersection while orthorhombic is (crystallography) has three unequal axes at right angles. Monoclinic and orthorhombic are two different kinds of crystal systems. Molecules or atoms in the case of a monoclinic crystal system are different to that of an orthorhombic Crystal system.

6. How many atoms are in orthorhombic?

Answer.  Although there are many crystal structures that fit with “orthorhombic” symmetry, the simple orthorhombic crystal structure has exactly 1 atom per lattice point in the simple orthorhombic Bravais lattice. Primitive orthorhombic crystals based on the Bravais lattice that exist with multiple atoms overall displaying primitive orthorhombic symmetry.

7. What is orthorhombic Sulphur?

Answer. Orthorhombic sulphur, Sα: The most significant form of sulphur is orthorhombic, Sα.  This is described as orthorhombic Sulphur,α Sulphur, Muthmann sulphur and rhombic sulphur by many. It is stable at room temperature and also at atmospheric pressure. Rhombic sulphur has a molecular structure. In the neighbouring molecules, the closest distance of approach of atoms is about 3.3A.

The entire experiment is based on the purpose of the heat generator that also derives from the Peltier effect application. 

Here, we find a different concept of the Peltier effect. The experiment called ‘Peltier effect’ was discovered by a French scientist in 1834. The concept was named after him.

This experiment is all about absorption or radiation of heat effect when there will be the passage of electrical current. We call the electrical junction a Peltier junction.

The concept of LJ effort is the fact where heat is given out when an electrical current is passed across the junction of two materials. Detailed information on the Peltier effect in thermocouple has been provided here.

Peltier Effect and Thomson Effect

The Peltier effect and Thomson effect possess some similarities. Thomson effect is something which states that the generation of reversible heat is possible when the passage of electrical current is sent via a conducting material under a certain temperature gradient.

The thermoelectric cooling devices are dependent on the Peltier effect. Each effect generated from the Peltier experiment is meant to convert the electrical energy into a temperature gradient.

However, we will study it later. Let’s clarify all your doubts on Peltier effect efficiency. The efficiency of the Peltier modules is found to be around 5% only. Also, it is concluded that there is an additional loss of 3% during the process.

(Image to be added soon)

In the above figure, the electric current is travelling through a circuit comprising two different Peltier materials. One Peltier device called a couple consists of one n-type and one p-type semiconductor pellet. 

The charge carries the negative electron and positive holes. This behaviour also promotes the transport of heat. Thermoelectric coolers (TECs) are used as Peltier effect devices. These devices are suitable for Peltier effect as they act as the beast heat exchanger between two electrical junctions.

The TECs Have Certain Benefits for Which it is Used in the Peltier Effect. Those Points Are:

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The Experiment of Peltier Effect Gives Two Annotations Such As

1. Heat is evolved at one junction

2. Heat is absorbed in the other junction

This is why the Peltier effect is considered as the converse of the Seebeck effect. So, the electric current is passed through a fuse consisting of its two dissimilar junctions. Heat is at one and absorbed at another junction. This is the basic output of the entire Peltier effect.

The Seebeck effect behaves like the opposite of the Peltier effect as they do not keep their function in one path but in two different ways. 

You can visualize from the figure that the current is able to pass within the two dissimilar natures, such as one is the absorption of heat, and another is releasing heat. 

Peltier Thermocouple

In a Cu-Fe thermocouple, the current flows from Cu to Fe, at junction number 1. In this case, the heat is absorbed. So, the thermocouple gets cooled.

(Image to be added soon)

However, in junction 2 you notice that the current flows from Fe to Cu and heat is liberated. That is why it gets heated. 

(Image to be added soon)

The reverse of the current occurs during this experiment. This initiates a healing effect at junction 1 and initiates the cooling effect at junction 2. This is why the Peltier effect is considered a reversible process. The reversible process is dependent on the direction of the current. 

The Peltier effect is a fact that depends on the passage of electric current and the absorption or rejection of heat current. Here, heat energy is absorbed or sent out from a homogeneous conductor. The Peltier effect is something that enables us to detect the different flows of electricity. 

The accompanying heat current is a type of electric current that can be explained by the different velocities of the flow of the electrons. All of these electrons are an active carrier of electric current. The electric flow of the current has certain velocities. Each electron’s velocity depends on the conduction electrons’ energies.

Peltier Coefficient

Peltier coefficient can be denoted as the total amount of heat evolved or absorbed at one end of the junction of a thermocouple during the passage of one ampere of current flows through it within one second (one coulomb). 

Pie ‘π’ is the symbol that is used for the Peltier coefficient. The unit of measurement is volt. Assume that H is the total heat absorbed or sent out at one point, then the formula for Peltier effect is:

H = π I t

Here, t = total time

I = current flow through the conductor

π = Peltier coefficient

Peltier electromotive force or Peltier emf is found at that junction where the Peltier coefficient is found. The co-efficient relies on certain facts such as the pair of metals in contact and the junction’s temperature.

The Sun is considered as the centre of our solar system which also consists of planets, satellites, etc. Hydrogen and Helium are the two most elements of its composition. It has a different structure consisting of Internal and external structure. Different ranges of temperature can be observed in these layers which have their own significance. In this article, we will cover one of these layers i.e. Photosphere of the sun. We will learn what is the photosphere, its definition, its features and other related aspects as well. This topic is very much essential in the fields of Astronomy, Geography, and Earth Science.

Introduction

The atmosphere of the sun is composed of different layers and gases. It has outer and inner layers. The inner layer of the sun is the core, radiative zone and convection zone while the photosphere, the chromosphere, the transition region and the corona are the outer layers of the sun. Out of these, we talk about the main photosphere which is the outer layer of the earth. The photosphere is the external layer of the Sun which is known as the luminous envelope or the visible layer of the sun from which light as well as heat radiate. The lowest visible layer of a star is the photosphere. It is located under the chromosphere and the corona. In the universe, the stars have no gases but the gas beneath the photosphere is opaque. So, the photosphere acts as their effective visible surface.

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Photosphere of the Sun

The lowest layer of the sun is the photosphere. It is the outer layer of the sun. The term photosphere derived from the ancient Greek roots, photos means “light” and sphaira means “sphere” which refers to being a spherical surface. It is the deepest region of the luminous object. It is composed of convection cells which are called granules. Granules are cells of plasma that are 1000 km in diameter with hot rising plasma in the centre and the cooler plasma laying in the narrow spaces between them. It is flowing at a velocity of 7 km/second. The thickness of the photosphere is 500 kilometres. At this layer, the energy of the sun is released in the form of light. This is the layer of the sun from which most of the light of the sun comes out. Because of the distance between the earth and the sun, the light of the sun reaches the earth in eight minutes. It is the most visible surface of the sun. It is the part from where the sun’s light reaches directly to the Earth. The sun is so distant from the earth as the edge of the photosphere appears sharp to the naked eye. But the sun has no surface because it is too hot to be a matter in it. But it is in the plasma state, that is a gas. The sun has so many gases composed of ionized atoms. 

The temperature in the photosphere ranges from  4,100 °C or 7,400 °F at the top to 9,700 °C or 17,500 °F. In this layer, photons that are generated are deeper. This cannot get out without any absorption and remission. The density of the ionized gas is the same as air at the earth’s surface. The density of ionized gas is 1/1,000. But it is more opaque. It is because of the absorption of the strong light by the hydrogen ions. 

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Definitions of Photosphere of the Sun

Some of the standard definitions are given below:

• “Photosphere is the visible surface of the sun, several hundred kilometres thick or a sphere of light or radiance or the luminous visible surface of the sun, being a shallow layer of strongly ionized gases.” – Collins Dictionary

Features of the Photosphere

The features of the photosphere are mentioned below:-

• The presence of dark sunspots.

• Bright faculae

• Granules

• By the Doppler effect, we can measure the material of the flow in the photosphere.

• It consists of super-granules and large scale flows as well as patterns of waves and oscillations.

• It is the most visible surface of the sun.

• The temperature of the photosphere is 5,780 degrees as compared to the temperature of the inside of the sun.

• It is measured in millions of degrees.

• The edge of the atmosphere is also measured in degrees.

• If we talk about the location of the photosphere, it is located above the solar convection zone where heat from the core radiates outward.

• The gases which are made in the photosphere are totally opaque means that we cannot see through them.

• The photosphere is constructed from the convection of the cells which are called granules.

• It produces a boiling effect and lives from 8-9 minutes.

• Sunspots are the cooler region of the photosphere. It is dark in colour because of its lower temperatures.

Sunspots

The areas which appear dark on the surface of the sun are called sunspots. It is a temporary phenomenon in the sun’s photosphere. It is darker than the other surrounding areas. It is the place where the magnetic field is about 2,500 times stronger than the earth’s. The most higher magnetic field is there than anywhere else in the sun. The temperature increases because of the strong magnetic field and the surrounding atmospheric temperature decreases. That is why the temperature in the sunspots turns lower than in the surroundings. 

The magnetic fields pointing in opposite directions, here sunspots occur in pairs. The region which appears as dark is called “umbra” and the region which is surrounded by light is called “penumbra.” The sunspots look dark because the surrounding surface of the photosphere is about 10,000 degrees Fahrenheit while the surface which is dark is about 6,300 degrees Fahrenheit. The disturbances in the sun’s magnetic field running over the photosphere which is the visible surface of the sun. The size of the sunspots is as an average or the same size as earth.

Why is the Photosphere Cooler than Corona?

As we all know, the photosphere is the visible surface of the sun. It is the first layer of the sun. It is the outer layer of the sun that is present outside of the core. Because of this, it is the coldest layer of the sun. The corona is the outermost layer of the sun and it is hotter than the photosphere. The chromosphere is the layer between the corona and photosphere. This layer of the Sun is considered the visible surface of the sun. The dark areas are present on it that are cooler than the surroundings. That is why the photosphere is
cooler than the corona.

Conclusion

To conclude, we said that the photosphere is the outermost layer of the sun. It is the lowest visible surface of the sun. It is a yellow coloured layer that is thick. The thickness of the layer is about 300 miles(500 kilometres). There are hot gases present in the layer which is known as sunspots. It is composed of convection cells i.e. granules. It is present in 1000 kilometres in the centre and it is flowing at the velocity of 7 kilometres per second. The temperature of the layer is 5,780 degrees as compared to the temperature in the sun. The gases which are present in the layer made it opaque. This article will help whenever you are studying the Sun and its various layers in Science or Astronomy.