Category: Physics Notes PPT

In 1945, an English scientist Michael Faraday FRS observed an effect while examining the effect of magnetic field on plane-polarized light waves. This effect was named after him as the Faraday Effect.

Faraday Effect is also known as the Faraday Rotation or the Magneto Optical Faraday Effect.

Faraday Effect causes the rotation of the plane of polarization (plane of vibration) of electromagnetic waves in particular substances in a magnetic field. 

This rotation varies proportionally with the projection of the magnetic field along the direction of the propagation of light.

This page discusses the observations of the Faraday effect, along with the Faraday Tyndall effect, and the Faraday effect in Layman’s terms.

Faraday Effect

The Faraday effect is a physical magneto optical Faraday Effect MOFE) phenomenon.

The Faraday effect results in a polarization rotation that varies proportionally with the projection of the magnetic field along the direction of the light propagation. 

Do You Know?

Faraday Effect is a special case of gyro-electromagnetism. 

The gyro-electromagnetism is achieved only when the dielectric permittivity tensor is diagonal.

History of Faraday Effect

The Faraday effect discovered this effect in 1845. It was the first experimental evidence that light and electromagnetism relate to each other.

James Clerk Maxwell completed the theoretical basis of electromagnetic radiation (including visible light) in the 1860s and 1870s and Oliver Heaviside. 

For most of the part, this effect occurs in optically transparent dielectric materials like liquids under the influence of magnetic fields.

The left and right circularly polarized waves propagating at varying speeds lead to Faraday. 

Therefore, the property of propagation is known as circular birefringence. 

As a result, linear polarization can decompose into the superposition of two equal-amplitude circularly polarized components of opposite handedness and different phases. 

Therefore, the Faraday effect induces the effect of a relative phase shift that rotates the orientation of a wave’s linear polarization.

Faraday Tyndall Effect

In the mid-1850s, Faraday spent an ample amount of time investigating the properties of light and matter. 

He made several hundred gold slides (thin enough to be transparent). These gold leaves were made by hammering the metal into very thin sheets (which were too thick for his purpose).

Also, he examined these thin sheets by shining light through them. However, Faraday used chemical means rather than mechanical.

For most of the part, his process involved washing the films of gold, which Faraday noticed produced a light/fainted ruby coloured fluid. 

                                       

Further, he kept fluid samples in bottles to use for future experiments: shining a beam of light through the liquid. 

In his record, Faraday observes that the cone was well-defined in the fluid by the illuminated particles.

As a result of this experiment, Faraday is known as one of the first researchers into nanoscience and nanotechnology.

Thus he realized that this cone effect was made because the fluid contained suspended gold particles that were too small to be observed with the scientific apparatus of the time, moreover,  which scattered the light to the side. This is known as the Faraday Tyndall effect in colloids.

Inverse Faraday Effect

The orbit of an electron directed by a circularly polarized light beam is usually a solenoid with an axis parallel to its displaced initial velocity. 

As a rule, the motion of the electron produces a solenoidal current that generates a magnetic moment depending on the direction of the shifted initial velocity.

The average of magnetic moments per unit volume in a free electron gas gives a plain microscopic explanation for the theory of the inverse Faraday effect in metals.

Inverse Faraday Effect in Optics

In optics, the inverse Faraday effect is the inverse of the Faraday effect. 

A static magnetization M(0) induces by an external vibrating electrical field with the frequency ω.  Here,  ω can be obtained with a high-intensity laser pulse.

Here, the induced magnetization lies proportionally to the vector product of E and E*.

M (0) α E (ω) and E* (ω)

From this equation, we see that the circularly polarized light with the frequency should induce a magnetization along with the wave vector k. 

Because [overrightarrow{E}] is in the vector product. Also, left- and right-handed polarization waves should induce magnetization of opposite signs.

Thus the induced magnetization is comparable to the saturated magnetization of the media.

Magneto Optical Faraday Effect

In physics, the Faraday effect, the Faraday rotation effect or the magneto optical Faraday effect are synonyms. To be simply speaking, the Faraday effect is the magneto optical phenomenon. 

A Faraday effect or the magneto optical phenomenon is the interaction between light and a medium. We refer to this phenomenon as the magneto optic Faraday Effect or MOFE.

Faraday Cage Effect

A Faraday cage a.k.a Faraday shield. It is a mesh or metallic enclosure that blocks electromagnetic fields. 

A Faraday shield is formed by a continuous covering of conductive material. 

In the case of a Faraday cage, a cage can be formed by a mesh of such conductive materials.

The Faraday cage works on the principle of an external electrical field that causes electrical charges to reside within the cage’s conducting material distributed so that they cancel the field’s effect in the cage’s interior.

Faraday cages protect sensitive electronic equipment from external RFI or the radio frequency interference.

They also consider devices that produce RFI, likewise radio transmitters, to prevent their radio waves from interfering with other nearby devices.

They also protect people and equipment against electric currents such as lightning strikes and electrostatic discharges.

       

                                     

As a result, the enclosing cage conducts current around the outside of the enclosed space and nothing passes through the interior.

Faraday Effect in Layman’s Terms

A dipole moment (usually just called “magnetic moment”) is something an object has that creates it and behaves sort of like a compass needle. 

It’s kind of a virtual compass needle enclosed within an object.
 

When the thing is placed during a magnetic flux, the thing rotates until its dipole moment is lined up with the magnetic flux. 

The dipole moment of a compass needle itself is, of course, parallel to the length of the needle; so is that of a magnet. 

A flat loop of wire with a circulating current also features a dipole moment, which is perpendicular to the loop; so once you place the loop during a magnetic flux, it’ll tend to rotate until it’s perpendicular to the sector (because then the moment of a magnet are going to be parallel to the field).

In atomic physics and quantum effects on atoms, the study of the hydrogen atom and their spectrum plays an important role. When the hydrogen spectrum was studied, physics noticed that the familiar red spectral line of the hydrogen atom consists of two closely spaced lines. That means the spectral line was split into two closely spaced lines or closely spaced doublet. The splitting of spectral lines is known as the fine structure or fine structure of spectral lines and it is considered one of the first pieces of experimental evidence for the electron spin.

Fine Structure of Hydrogen Atom

The fine structure of the hydrogen atom is also known as the hydrogen fine spectrum. We know that the hydrogen atom is one of the simplest forms of atom available, which consists of a single electron in its valence shell. Before we start with the fine structure of the hydrogen atom let us have a look at the spectrum of the hydrogen atom. The spectrum of a hydrogen atom consists of different series of spectral lines and these sets of spectral lines fall into a different region of the electromagnetic spectrum, for example, the Balmer series lies in the visible region of the electromagnetic spectrum. 

Now, what is the fine structure of a hydrogen atom? When we examine the Balmer series of spectral lines we know that it consists of four different spectral lines corresponding to violet, blue, green, and red wavelengths. When spectral lines of the hydrogen spectrum were examined under a high-resolution spectrometer it was found that a single spectral line appears to be resolved into two pairs of closely spaced single lines such that these split lines will be having slightly different wavelengths. This splitting spectral line is known as the fine structure of a hydrogen atom.

When the red spectral line which is also known as The line is closely examined with high-resolution spectrometers, physicists found that it consists of two closely spaced doublet lines due to spin-orbit coupling. We know that the electrons are revolving around the nucleus in definite orbitals and due to the orbital motion of electrons a magnetic field is generated. When the spin electron magnetic moment interacts with the magnetic field, this interaction is familiarly known as spin-orbit coupling. 

In atomic spectroscopy, the energy levels of electrons of an atom are given by the formula:

[n^{2s+1}l_{j} … (1)]

Where,

n – The principal quantum number

s -The spin angular momentum quantum number

l -The orbital angular momentum quantum number

j -The total angular momentum quantum number (i.e., the sum of both spin and orbital angular momentum i.e., [(l pm s)]

Depending upon the value of l different orbits or energy levels are designated, for example, for l =0 we have S-orbit, for l =1 we have P-orbit, and so on.

Fine Spectrum

The fine structure of the spectral line describes the splitting of spectral lines due to the electron spin and the relativistic correction to the total energy of the hydrogen atom electron. When electrons transit from lower energy levels to higher energy levels by absorbing the energy, they will be unstable and hence lose their energy in the form of photons of different wavelengths that further result in a spectrum.

The interaction between the magnetic field generated due to the relative motion of the nucleus and the electron spin angular momentum will result in the splitting of the energy of electrons into two energy levels.  

The electron with [+frac{1}{2}] will have a magnetic spin momentum and experience a torque due to the presence of a magnetic field and hence it will rotate it, at the same time, the electron with [-frac{1}{2}] will also have some magnetic spin momentum and experience a torque due to the presence of magnetic field and hence it will rotate it in opposite direction. As the electron rotates, there will be a change in its internal energy and it is given by:

[Rightarrow  U = -mu B]

(Note: since they rotate by a different amount, hence they will also have a different amount of energy)

Suppose that the electron in hydrogen atom transit from 1s level to 2P level, we know that the motion of the electron is associated with the orbital quantum number and the spin quantum number. When the electron is in the 1S state it is in its orbit and hence a single energy level is obtained, whereas the 2p state due to spin-orbit interaction splits into two levels. Mathematically, we write:

[Rightarrow  j = (1pm s) …(1)]

For P-orbit the value of l is 1and we know that the spin quantum number of the electron is 12. substituting, these values in equation (1) we get,

[Rightarrow j = frac{3}{2} , frac{1}{2}]

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Thus 2P level is split into two energy levels. Thus, when the transition of an electron from 1S to 2P is observed we notice only a single spectral line, when it is observed through a high-resolution spectrometer, we notice that there are two closely spaced spectral lines with slightly different wavelengths, and this splitting of spectral lines is known as the fine structure of hydrogen atom or the fine spectrum.

Fine Structure of H Alpha Line

The H-alpha(H)line is a specific deep-red visible spectral line found in the Balmer series and the wavelength of the H-alpha is around 656 nm. The H-alpha line originates when the electron transit from its third to second lowest energy level. The H-alpha line is one of the brightest spectral lines in the Balmer series. 

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More About Fine Structure:

The fine structure is the breaking of an atom’s primary spectral lines into two or more components, each indicating a slightly different wavelength, in spectroscopy. When an atom transitions from one energy state to another, it produces light, which creates a fine structure. The split lines, also known as the fine structure of the main lines, result from the interaction of an electron’s orbital motion with its quantum mechanical “spin.” An electron may be compared to an electrically charged spinning top, and as a result, it behaves like a little bar magnet. The fine structure is created when a spinning electron interacts with the magnetic field created by the electron’s revolution around the atomic nucleus.

The fine-structure constant is a dimensionless constant that describes the amount of splitting.

Alkali metal atoms, such as sodium and potassium, have two fine structure components (called doublets), whereas alkaline earth atoms have three fine structure components (called triplets) (triplets). This is because alkali metal atoms have only one electron outside of a closed core, or shell, of electrons, whereas alkaline earth atoms have two. With increasing atomic number, doublet separation for matching lines rises; therefore, a doublet with lithium (atomic number 3) may not be resolved by an average spectroscope, but a doublet with rubidium (atomic number 37) may be widely separated.

When a light source is put in a magnetic field, the Zeeman effect occurs, dividing a spectral line into two or more components of slightly different frequencies. Pieter Zeeman, a Dutch scientist, first noticed it in 1896 as a thickening of the yellow D-lines of sodium in a flame held between strong ma
gnetic poles. Later, it was discovered that the widening was caused by a distinct splitting of spectral lines into up to 15 components.

Zeeman’s Discovery

Zeeman’s discovery won him the Nobel Prize in Physics in 1902, which he shared with fellow Dutch physicist, Hendrik Antoon Lorentz. Lorentz theorized that the oscillations of electrons inside an atom generate light and that a magnetic field would impact the oscillations and hence the frequency of the light emitted. Lorentz had previously devised a hypothesis concerning the effect of magnetism on the light. This idea was validated by Zeeman’s study and later updated by quantum mechanics, which states that as electrons transition from one discrete energy level to another, spectral lines of light are emitted. In a magnetic field, each of the levels, which is defined by its angular momentum (a quantity related to mass and spin), is divided into substates of equal energy. The ensuing patterns of spectral line components reflect these energy substrates.

The Zeeman effect has aided physicists in determining and identifying the energy levels of atoms in terms of angular momenta. It also makes it possible to investigate atomic nuclei and phenomena like electron paramagnetic resonance. The pattern and quantity of splitting indicate the presence of a magnetic field as well as its intensity. The quantum number L can have non-negative integer values. The magnetic field splitting in terms of levels may be determined using the formula 2* L+1.

The Balmer series lines we observe are creatively referred to as alpha, beta, and gamma.

When an electron travels between the second and third orbits (N=2 and N=3), a line forms in the red section of the spectrum, and the wavelength at which this happens is 656nm. The Hydrogen-alpha line is named after it, and hydrogen alpha filters are designed to block out as much of the spectrum as possible, leaving just a very small bandwidth for light with the H-alpha frequency to pass through.

Did You know?

• Spectral lines give information on the nucleus. The main effects are isotope shift and hyperfine structure.

• The study of the hyperfine structure of the H alpha line is of importance in many fields of science. The emission of the H alpha line determines many features of the solar atmosphere including prominences and the chromosphere.

In general terms, we say that the push or pull of an object is force, but what does this mean? 

A force is defined as the application of push or pull on an object with a mass in such a way that it will affect the motion of an object when unopposed. It can cause an object to move from its state of rest, i.e., change its velocity (to accelerate) or can change its direction of movement. It is an interaction that causes or changes the motion of an object. When a force is applied, it has both magnitude and direction. Hence, it is a vector quantity. 

It is denoted by the symbol F and its S.I. unit is Newton (N). The other units of force are dyne,kgwt, etc. 

Now, let us understand the push and pull force in basic language.

What is a Push Force? 

Push is defined as a force that causes an object to move away from the person who is applying the force from its state of rest. When an object is pushed, it tends to move away. Kicking a ball, closing a door, pushing a trolley, and inserting a plug into the socket are all examples of push force.  

Assume that you are asked to push a lawn roller or push the luggage from the stairs and throw it on the floor. For this, you will have to put an effort and that effort you apply through your feet to the object you are pushing is the push force. Applying this force is easier; however, there is another category of force that demands a lot of energy from your end. This force type is called the pull force. Now, let us understand what it is!

What is a Pull Force? 

The pull is defined as a force that causes an object to move towards the person who is pulling the object. Opening a door, plucking the string of a guitar, drawing a bucket of water from the well, and pulling the curtain are all examples of pull force. 

So, this was all about the force in general. Now, let us understand its types.

 

Types of Forces

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A force can be applied to an object in two ways, i.e., by making a contact with the object or by not making a contact with the object. Based on that, there are two types of forces. They are known as contact forces and non-contact forces. 

Contact Force

A contact force is defined as a force that requires a contact to apply a force on an object. Kicking a ball and closing a door are all examples of contact forces because contact is made in each case. It is further classified into three forces, namely, frictional force, applied force, and normal force.

• Frictional Force: When a ball is softly kicked, it rolls over the floor. At that time, a force acts opposite to the direction of the moving ball which eventually stops the ball. This type of force is called frictional force. Generally, it resists the motion of the object when the surface of an object comes in contact with the surface of another object.

• Applied Force: When a person or an object applies force on another object, which results in the movement of the object. It is called an applied force.

• Normal Force: When an object is resting upon a surface, the surface exerts an upward force to balance the force exerted by the weight of the object. The upward force is known as the normal force which is applied by the surface. 

Non-Contact Force 

Non-contact force is defined as a force that is exerted without making any contact. It is further classified into three forces. They are gravitational force and magnetic force. 

• Gravitational Force: The attraction between any two objects with mass is known as gravitational force. It is a natural phenomenon. Stars, planets, and galaxies have an attractive force acting between them all the time. On Earth, physical objects possess weight due to gravity and the ocean tides occur due to the Moon’s gravity.

• Magnetic Force: A magnetic force is defined as a force exerted between two poles of a magnet and also between electrically charged moving particles. It can be either attractive or repulsive.  

Did You Know?

It is assumed often that if an object is at rest, no force is acting on it. But, this is not true. When an object is at rest, there are two forces that  act simultaneously on it. One is the gravitational force which acts downwards and the other one is the normal force which acts upwards. These two forces balance each other. Hence, the net force acting on the ball is zero. Now, if the ball is kicked, then only it will move from its stationary position because an external force greater than the other two forces is applied to it now. Hence, it will move in a particular direction. 

So, this was all about pushing and pulling along with the types of forces. Now, let us assume that your mother asked you to pull heavy luggage from one cart and put them into another cart in the first case. In another situation, she just asks you to drag the luggage, which one would you prefer the easier task? Well, dragging is easier. Here, dragging is a push force, on the other hand, taking out luggage from one cart to another is a pulling force. This is the reason we say that pushing is better than pulling. 

The Gibbs free energy, also commonly known as the Gibbs function, Gibbs energy, or free enthalpy, is a thermodynamic potential that is used to measure the maximum amount of work done in any given thermodynamic system when the temperature and pressure of the system are kept constant. Gibbs free energy is denoted by the letter G. Its value is usually expressed in either Joules or Kilojoules as it is also a form of energy. Gibbs free energy is defined as the maximum amount of work done that can be extracted from a closed thermodynamic system.

Gibbs energy is a thermodynamic property and it was determined by American scientist Josiah Willard Gibbs in the year 1876 when he was conducting experiments to predict the behaviour of systems when combined together or whether a process could take place simultaneously and spontaneously at a given temperature. Gibbs free energy was also known as available energy. Gibbs free energy can be visualized as the total amount of useful energy present in a thermodynamic system that can be utilized to perform some work.

 

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Gibbs Energy

Gibbs energy is also known as Gibbs free energy, it is one of the four thermodynamic potentials. Gibbs free energy is equal to the difference in enthalpy of the system with the product of the temperature and entropy. The equation is given as:

G= H – TS

Where,

G = Gibbs free energy

H = enthalpy

T = temperature

S = entropy

Gibbs free energy is a state function thus it doesn’t depend on the path (i.e., its path independent entity). Thus, the change in Gibbs free energy will be equal to the difference in the change in enthalpy with the product of temperature and entropy change of the system.

ΔG= ΔH – Δ(TS)

If the reaction is carried out under constant temperature i.e., assuming that the reaction is isothermal in nature, (ΔT=0) then:

ΔG= ΔH – TΔS

This equation is called the Gibbs Helmholtz equation.

Now, depending on the value of the change in Gibbs free energy, we can define many new reactions:

• Suppose the change in Gibbs free energy is greater than zero (ΔG > 0), then the reaction is nonspontaneous and endergonic.

• Suppose the change in Gibbs free energy is less than zero (ΔG < 0), then the reaction is spontaneous and exergonic.

• Suppose the change in Gibbs free energy is equal to zero (ΔG = 0), then the reaction is at equilibrium condition.

There are some important key points to be remembered regarding Gibbs free energy such as:

1. According to the second law of thermodynamics, the entropy of the universe always increases for a spontaneous process and it can never be equal to zero.

2. The change in Gibbs free energy (ΔG) determines the direction and extent of chemical change.

3. The change in Gibbs free energy (ΔG) is useful only for reactions in which the temperature and pressure remain constant (i.e., it is in good agreement with the isothermal and isobaric process). The system is usually open to the atmosphere (constant pressure) and we initiate and terminate the process at room temperature (after any heat we have supplied or which is released by the reaction has dissipated).

4. Standard Gibbs free energy is often used as the single master variable that determines whether a given chemical change is thermodynamically possible. Thus, if the change in free energy of the reactants is more than that of the products, the entropy of the world will increase when the reaction takes place as written, and so the reaction will tend to take place spontaneously. 

       ΔS_universe =  ΔS_system + ΔS_surroundings

5. If the change in Gibbs free energy is negative, the process will occur spontaneously and is referred to as exergonic.

6. Therefore spontaneity of the reaction is dependent on the temperature of the system (Gibbs free energy spontaneous).

Even though the change in Gibbs free energy is temperature-dependent, we assume the change in enthalpy ΔH and the change in entropy ΔS independent of temperature when there is no phase change in the reaction. So if we know the change in enthalpy ΔH and the change in entropy ΔS, we can calculate the change in Gibbs free energy ΔG at any temperature.

 

Relationship Between Free Energy and Equilibrium Constant

The change in Gibbs free energy of the thermodynamic reaction in any state, ΔG (at equilibrium) is related to the standard free energy change of the reaction, ΔG° (that is equal to the difference in the free energies of creation of the products and reactants both in their standard states) 

 

According to the equation:

ΔG = ΔG⁰ + RT In Q

Where,

Q- The reaction quotient.

ΔG=0 and Q become adequate to the constant. Hence the equation becomes,

⇒ ΔG⁰=-RT ln K_eq

⇒ ΔG⁰= -2.303 RT log K_eq

Where,

R=gas constant = 8.31 J mol^-1 K^-1 or 0.008314 kJ mol^-1 K^-1 

T is the temperature on the Kelvin scale

In any reversible reaction, the free energy of the reaction mixture is less than the free energy of reactants also as products. Hence, Gibbs free energy decreases whether we start from reactants or products i.e, ΔG is -ve in both backward and the forward reactions.

Relationship Between Gibbs Free Energy and EMF of a Cell

In the case of galvanic cells, Gibbs energy change ΔG is said to be the trade done by the cell.

ΔG = – nFE_cell

Where,

n = no. of moles of electrons involved

F = the Faraday constant

E = emf of the cell

We know that 1 Faraday=96500 coulombs.

Did You Know?

• We know that both the enthalpy of the system and the Gibbs free energy are the thermodynamic potentials, and one of the unique facts is that even the unit of ΔG is the same as that of ΔH.

• The tesla free energy is modern fr
  ee energy, though it is named free energy it is not free, it requires components. Usually found in a free electricity generator or free energy motor.

• A free energy generator magnet follows a mechanism that generates electrical energy using the neodymium magnet theory. There are various sizes of generators, and one kind of generator that produces electrical energy is the free energy generator.

What is a Galaxy?

Mother Earth, our home planet, is a part of the solar system which consists of 9 planets (including Pluto). The solar system where we live is a part of the Milky Way Galaxy.

A galaxy is a system of millions of stars consisting of gas and dust which are bound by each other through gravitational force. Our Milky Way Galaxy has a supermassive black hole and its centre is known as “Sagittarius A.”

During night time, we can see the stars of the Milky Way Galaxy if we look up in the sky. We can also have a choice to view the diary band of the Milky Way, when it is too dark at night and far from citylights.

Besides our Milky Way galaxy, there are millions and millions of galaxies in the known universe. The Hubble Space Telescope discovered more than 10,000 galaxies by viewing a small part of space continuously for 12 days.

What is the Milky Way?

Our Sun is a star, which is the central part of our solar system. The Sun along with the planets is part of the Milky Way galaxy. A galaxy is a system of stars, dust and gas which are bound by gravitational force. Galaxies are found in various sizes, shapes and colors.

The Milky Way is our home galaxy. The Milky Way is spirally shaped having length of about 1,00,000 light-years, and width of 10,000 light-years. It contains billions of stars which include our sun. You can get a glimpse of the band of stars in the Milky Way from a dark place at night. Our solar system is located somewhere between the centre and the edge of the Milky Way.

The band of the Milky Way is usually seen from dark sky areas. Scientists or space lovers use the Atacama Large Millimeter/sub-millimeter Arra (ALMA) antenna to see it.

What Galaxy is Earth in?

The Milky Way: It is the home galaxy of our planet. The spiral arm of the Milky Way is made up of giant clouds of gas and dust with star clusters. Some parts of the galaxy are also made of dark matter. Our galaxy consists of four spiral arms which emerge from the central bar.

What Type of Galaxy is the Milky Way?

Barred spiral galaxy- The shape of the Milky Way galaxy is of barred spiral type. The stars that we see at night are part of it. The galaxy appears as a milky band of light in the sky, that’s why it is called the Milky Way Galaxy.

A bright band of light stretches across the sky in the night sky. It can be seen from naked eyes when the sky is very dark. This band is the disk of stars that forms the structure of the Milky Way. It depicts that the Milky Way is flat.

What is the Milky Way Made of?

The Milky Way galaxy is made up of approximately 90% dark matter and about 10% “luminous matter.” This large amount of dark matter initiates an invisible halo which causes the Milky Way to spin.

What are the Types of Galaxies?

There are basically four main types of galaxies:

• Elliptical

• Irregular

• Spiral

• Barred spiral

These main categories of galaxies are further divided into subcategories. Some other types of galaxies also exist based on their size and other features.

● The most common type of galaxy found in the universe is the spiral-shaped galaxy. Almost 77% of the galaxies discovered till date are spiral shaped galaxies. For example, the Andromeda galaxy is a spiral shaped galaxy.

●  A majority of spiral galaxies have a bar-like structure called a barred-spiral galaxy. Around two-thirds of spiral galaxies are barred shaped. Our Milky Way galaxy is a barred shaped galaxy.

●  An elliptical doubled-ringed galaxy is the rarest type of galaxy. The galaxy PGC 1000714 is such a type of galaxy. According to scientists around 0.1% of galaxies are of this type. It is also called the Hoag-type galaxy.

●  Irregular galaxies are also found, which are usually smaller in size. Around a quarter of known galaxies are irregular in shape. These galaxies don’t have a distinct shape and give a chaotic appearance.

●  Elliptical galaxies are also found which are usually composed of old stars having a low mass. They normally occur in Virgo superclusters. Around 10 – 15% of known galaxies are of this type. The starlight from these galaxies is very dim as compared to spiral galaxies.

Geostrophic motion is a fluid flow that occurs in a direction parallel to the lines of equal pressures/isobaric in a rotating system, such as the Earth. 

A Geostrophic flow occurs by the balance of the Coriolis force (a force caused by the Earth’s rotation), and the pressure-gradient force (when the friction is low).

Hence in a geostrophic flow, instead of water moving from a high-pressure region to a low-pressure region, it moves along with the lines of equal pressure and this happens because of the Earth’s rotation.

On this page, we will understand what Geostrophic motion, pressure-gradient  force is and Geostrophic flow is all about.

What is a Geostrophic Motion?

From the above text, we understand that water does not flow from a high sea level to a low sea level, it just gets along with the lines of equal pressure. 

The velocity of the flow varies directly with the pressure gradient and conversely with the latitude. 

In practical, observed fluid flow is not strictly geostrophic, though large-scale oceanic and atmospheric movements approach the ideal stage. It means that the geostrophic current usually portrays the actual current within around 10 percent, provided the comparison is made over large areas and there is a little curve in the isobars.

Pressure-Gradient Force

The pressure gradient quantifies the lowering of the atmospheric pressure in an area at a specific time. For instance, gale force winds turn into a light breeze in a specific city after an hour. 

A pressure-gradient force is a relative force that is calculated when there is a difference in pressures. The below diagrams shows the relative pressure difference:

Geostrophic Flow

A geostrophic current is an oceanic current in which the pressure-gradient force is balanced by the Coriolis effect or the Earth’s rotational force. 

The direction of geostrophic flow is parallel to the lines of equal pressure/isobars, with the high-pressure to the right of the flow in the Northern Hemisphere, and the high-pressure to the left in the Southern Hemisphere. 

The concept of Geostrophic current is taken from weather maps, whose isobars show the direction of geostrophic flow in the atmosphere. 

The below image shows that surface currents generally mirror average planetary atmospheric circular patterns:

Geostrophic flow can either be barotropic or baroclinic. A geostrophic current can be assumed as a rotating shallow-water wave with a zero frequency. 

The geostrophic principle is useful for oceanographers because it helps them infer ocean currents from measurements of the sea surface height (by combined satellite altimetry and gravimetry) or from vertical profiles of seawater density taken by ships or autonomous buoys. 

Do You Know the Examples of Geostrophic Currents?

Examples of Geostrophic Currents

The major currents of the world’s oceans, like the Gulf Stream, the Agulhas Current, and the Antarctic Circumpolar Current,  the Kuroshio Current are all approximately in geostrophic balance and hence they are considered examples of geostrophic currents.

Concept of Geostrophic Motion

You may think about how an oceanographer changes overestimations of the surface slope into a current speed. The premise supposition will be that when we take a gander at the huge flows oversized of 100 km or more there is a considerable balance between two forces – the pressure gradient and the Coriolis force.

Now, let’s understand the concept of Geostrophic flow through ocean currents.

Ocean Currents

Now, talk about the ocean current.

Imagine for a moment (an ideal situation) that there is a ‘high’ and a ‘low’ level in the sea surface (an altimeter can measure this( and that there is no Coriolis effect. 

In the absence of Coriolis force, water would naturally flow from the high to the low region in order to restore the equilibrium. In other words, there is a force that pushes the water from the high level to the low level – and if this force lies proportionally to the difference in levels, then it is the ‘pressure-gradient ’.

Now, considering that Coriolis force occurs on the water. Now, it will pull the current to the right in the Northern hemisphere (as shown in the figure below) and to the left in the Southern hemisphere.

Geostrophic Balance

A time comes when the pressure-gradient force becomes equal to the Coriolis force, the balance between these two forces on a parcel of the water is what we state as the Geostrophic balance. The below image represents the above statement:

So, when the situation is the same as depicted in the figure above, we say that there is a geostrophic balance and that the current is purely geostrophic.

The best part is, an oceanographer can compute the current by the measurement of the slope.

So, let’s understand the Geographic Wind in brief.

Geostrophic Wind                   

The geostrophic wind is a theoretical wind directed along with isobars, i.e., the lines of constant pressure at a given height. This balance rarely holds exactly in nature. 

However, the real wind somewhat differs from the geostrophic wind (imaginary wind) because of the other forces such as friction from the ground. 

From the above diagram, we see the deviation of a real wind from its original path; however, geostrophic wind seamlessly flows without getting affected by any force.

Do You Know?

The suspicion that there is geostrophic balance is just precise when we take a gander at the large-scale flows, for example at scales bigger than a few tens of km. All the significant currents can be considered geostrophic to a first estimate. 

At more limited sizes, the geostrophic (non-geostrophic) segments of the flows, for example, because of the force by the neighborhood wind, become increasingly significant. 

In several coastal areas, the dissemination is to a great extent geostrophic. An altimeter can anyway still be utilized to measure the geostrophic part.