Category: Physics Notes PPT

All matter which we can move that too from one state to another. It may require very extreme temperatures or we can say that extreme pressures but it can be done. Sometimes we can say that a substance doesn’t want to change its states. we have to use all of our tricks when that happens to us. 

To create a very solid we might have to decrease the temperature to by a huge amount and then add pressure. For example we can say that the oxygen which is O₂ will solidify at -361.8 degrees Fahrenheit that is -218.8 degrees Celsius at pressure which is standard. However we can say that it will freeze at a temperature which is warmer when the pressure is increased.

Change of State Explained

Some of us may already know about liquid nitrogen written as N₂. It is nitrogen from the atmosphere which is basically in a liquid form and it has to be super cold as well to stay a liquid. What if we wanted to turn this nitrogen into a solid but we couldn’t make it cold enough to solidify? 

In this case, we could increase the pressure which is in a sealed chamber. Eventually we would reach a point where the liquid becomes solid. If we have liquid water denoted as H₂O at room temperature and we wanted water vapor gas, we could use a combination of temperature which is high or low pressures to solve your problem.

The Change of State from Solid to Liquid

The change with the phase that happens when we reach certain special points. Sometimes we can say that a liquid which wants to become solid. Scientists usually use something known as a freezing point or melting point to measure the temperature at which a liquid turns into a solid completely. 

There are physical effects that can change the melting point. The pressure is one of those effects. When the surrounding pressure of a substance increases the point which is freezing and other special points also go up. It is easier to keep things which are solid when they are under pressure which is greater.

Generally we can say that the solids are more dense than liquids because their molecules are together closer. The process of freezing compacts the molecules into a space which is smaller.

There are always exceptions which are in science. Water is a very special level of which are of many levels. It has more space which is between its molecules that are when it is frozen. The molecules which are organized in a specific arrangement take up more space than when they are all loosey-goosey in the state of liquid. Because the number which is the same as molecules take up more space and water which is solid is less dense than water or liquid. There are many other types of molecules which are organized in water which is solid.

Solid to Liquid is Called 

Imagine that we are a solid. We are a cube which is ice sitting on a counter. we dream of becoming water liquid. We need some energy here for this. Heat is probably a process which is the easiest energy we can use to change your physical state. The atoms which are in a liquid which is more energy than the solid atoms.

There is a temperature which is special for every substance known as the melting point. When a solid reaches the temperature that is of its melting point it can become a liquid. For the temperature of water that needs to be a little over zero degrees Celsius that is 0oC for you to melt.

Change of State Observation

If it were salt or sugar or the rock our melting point is higher than that of water. How do we know that fact? If their point which is melting were lower they would also be temperature which is of liquids is above zero degrees Celsius. The reverse of the process of melting which is called freezing. The water which is of Liquid freezes and becomes ice solid when the molecule’s energy is lost.

We know about melting solids and becoming liquids. Some of us may have also seen a solid become a gas. It’s a process known as sublimation. The example which is easiest of sublimation might be dry ice. The dry ice is solid carbon dioxide CO₂. Amazingly we can say that when we leave dry ice out in a room it just turns into a gas. Have we ever heard of liquid carbon dioxide? It can be made but not in a situation which is normal. Coal is an example or we can say another example of a compound that will not melt at normal atmospheric pressures. It will sublimate at a very high temperature which is high.

Practical Application

Can we go from a gas to a solid? Yes Sure. the deposition that occurs when a gas becomes a solid without going through the states of liquid of matter. Those of us who live near the equator may not have seen it but even closer to the poles which we see frost on morning of winter. Those little crystals of frost which are on plants build up when water vapor from the air becomes a solid on the leaves which are of plants. 

The Matter which is in everyday life exists in three forms that are liquid, solids and gases. In this article we will examine the interchangeability of the states one by one which are of matter and examine the conditions that are required for such a change to occur. The Changes which are in the state which is of matter that occur through changes in the energy of the substance are mainly thermal energy. 

The molecules that are supplied with energy that is the heat which start vigorously vibrating. If even more energy which is supplied for the molecules that eventually gain energy which is enough to separate out of the sample. We can best understand the concept that if we try to apply this practically.

In order to understand the concept of coefficient of friction, we must be well versed with friction, friction force, and type of friction. A surface can be classified as frictional if it resists relative motion between two surfaces in contact, for example, two surfaces might be in contact while sliding or rolling, or resting. Rough surfaces are usually responsible for friction. It means that if the surfaces are not designed for motion, the relative motion between them will lead to friction. Surface roughness is always directly correlated with friction. Surfaces with more roughness experience more friction. Smoother surfaces will have less friction than rough ones.

Friction Force or Force of Friction

In a vector quantity, the friction force has both a magnitude and a direction. In simpler terms, friction is a reaction force. In other words, the friction force doesn’t exist directly, it’s the reaction of another force on the body. Additionally, friction is a resistive force. 

The formula for the coefficient of friction

In terms of friction between two surfaces, the coefficient of friction indicates the amount of interaction between the two surfaces. Surface roughness can be determined by the coefficient of friction value. Any object under observation experiences friction when it is subjected to the normal force acting on it. This can be expressed mathematically as follows:

⇒Fᵣ ⍺ N …… (1)

 An object of mass m is placed horizontally on a rough surface (and even inclined). As the object’s weight acts downward, the block’s normal force is in the opposite direction as the weight of the object. Assuming that the block is moving to the left, the friction force will be directed to the left as well.

There exists a direct relationship between the friction force and the normal force acting on it, but this relationship breaks down when a coefficient of friction is introduced. 

Mathematically, we write:

⇒Fᵣ=μN……..(2)

Where,

μ – The coefficient of friction

⇒μ=Fᵣ / N ………(3)

 

A coefficient of friction equation can also be known as the coefficient of friction formula. It is clear from equation (3) that friction causes force to be directly proportional to the friction coefficient. It stands to reason that if the coefficient of friction is greater, then the force of friction will also be greater.

The formula for static friction

When an object is at rest, static friction is defined as the tendency to move relative to it. The force of static friction acts even before we slide the object as long as the normal force exists between the two surfaces. 

The static friction formula is given by:

 ⇒ Fₛ=μₛN

Where, 

μₛ- Coefficient of static friction.

⇒μₛ=Fₛ / N……..(1)

Equation (1) is known as the coefficient of static friction formula.

The formula for Kinetic Friction:

In its simplest form, kinetic friction is the resistance to relative motion between surfaces when the motion starts. The formula for kinetic friction can be translated as follows:

 ⇒ Fₖ=μₖN

Where,

 μₖ- Coefficient of kinetic friction

⇒ μₖ=Fₖ / N

The above expression is known as the Coefficient of kinetic friction formula. 

Did You Know?

Every material will have a different coefficient of friction depending on the roughness of its surface. For example, if you slide the glass over the glass, you can slide easily without any jerk in the motion. At the same time, if you slide a piece of glass over a road or any unfinished surface, the motion will not be smooth and observe variation in the force. 

Let us have a look at the coefficient of friction of a few materials as listed below:

 

There are also coefficients of friction calculators available which will ease our calculation while doing numerical.

Theory and Importance

Compton effect refers to the increase in the wavelength of photons (X-rays or gamma rays), due to their scattering by a charged particle (usually an electron). The impact has ended up being one of the foundations of quantum mechanics, which represents both wave and particle properties of radiation.

The American physicist Arthur Holly Compton clarified (in 1922 and distributed in 1923) the frequency increment by considering X-rays as made out of discrete heartbeats, or quanta, of electromagnetic energy. The American physicist Gilbert Lewis later authored the term photon for light quanta. 

Photons have energy and force similar to material particles. They also have wave nature, for example, frequency and recurrence. The energy of the photon particle is dependent on its electromagnetic frequency. Photons of low energy therefore have low frequencies and longer wavelengths.

The singular protons collide with the free and loosely bonded electrons present in the atoms of the matter. Impacting photons move a portion of their energy and force to the electrons, which like this pullback. In the moment of the impact, new photons of less energy and force are delivered that dissipate at points the size of which relies upon the measure of energy lost to the withdrawing electrons. Due to the connection between energy and frequency, the dispersed photons have a more extended frequency that additionally relies upon the size of the point through which the X-rays were redirected. The decrease in frequency, or Compton shift, doesn’t rely upon the wavelength of the incident photon.

What is Compton Scattering?

Compton scattering is a case of inelastic dispersing of light by a free charged molecule, where the frequency of the dispersed light is not quite the same as that of the incident radiation. In Compton’s unique test the energy of the X-ray photon (≈17 keV) was a lot bigger than the coupling energy of the nuclear electron, so the electrons could be treated as being free in the wake of dispersing. 

The sum by which the light’s frequency changes is known as the Compton move. Albeit atomic Compton dissipating exists, Compton dispersing alludes typically to the communication including just the electrons of a molecule. 

The Compton impact was seen by Arthur Holly Compton in 1923 at Washington University in St. Louis and further checked by his alumni pupil Y. H. Charm in the years following. Compton procured the 1927 Nobel Prize in Physics for the disclosure. 

The impact is huge as it shows that light can’t be clarified simply as a wave marvel. Thomas dispersing, the traditional hypothesis of an electromagnetic wave dissipated by charged particles, can’t clarify shifts in frequency at low force. Traditionally, the light of adequate power for the electric field to quicken a charged molecule to a relativistic speed will cause radiation-pressure to withdraw and a related Doppler effect to take place of the dissipated light. However, the impact would turn out to be self-assertively little at adequately low light powers paying little heed to frequency. Hence, light acts as though it comprises particles, on the off chance that we are to clarify low-power Compton scattering.

Difference Between Compton Effect and Photoelectric Effect

The photoelectric effect happens in the bound electrons, while Compton impact happens in free and loosely bound electrons.

In the photoelectric effect, the energy of the photon is consumed by the electron. While in the Compton effect, a photon is dissipated.

A superior method to examine this is to understand that in the photoelectric impact, the electromagnetic wave couples two-electron states (bound and energized) by means of the recurrence contrast which those states share with the electromagnetic wave. In the Compton impact, there is additionally an electromagnetic wave and two-electron states (in a focal point of-mass framework we can think of them as approaching and active). Yet in this framework, it is the frequency, not the recurrence contrast, which couples the electromagnetic wave to the electron states. This is generally obvious on account of a head-on “impact” where the superposition of the approaching and active electron states makes compelling diffraction grinding of equal sheets of charge, which is absolutely impenetrable to an approaching electromagnetic wave.

Zodiac Constellations

Thousands of stars can be visible to the naked eye on a clear and dark night. We can create shapes and patterns by using these stars and our creativity. The patterns which are made from a group of stars are called constellations.

Ancient people were aware of these constellations and named them after some objects and animals they resembled. They also made stories about the constellations. For example, the constellation Perseus, Cetus, Andromeda, Cassiopeia, and Pegasus are part of Greek mythology. Different cultures name the constellations by similar names, like Pisces – fish in Greek and Meena – fish in Sanskrit.

Zodiac and Constellations

Since the Earth rotates from west to east, the constellations also appear to move in the sky from west to east. The constellations of the Northern Hemisphere are not visible from the Southern Hemisphere, and vice versa. That’s because the Earth is spherical, and some constellations don’t fall in the line of sight. However, people from the equator are able to see all the constellations.

All Zodiac Constellations

All total, you can find 12 major constellations that line-up around the sun’s path along the sky; otherwise known as ecliptic. These are called as zodiac zodiac constellations: 

Aries (Mesha), Gemini (Mithuna), Taurus (Vrushabha), Leo (Simha), Crab/Cancer (Karka), Virgo (Kanya), Scorpion (Vrushika), Libra (Tula), Capricorn (Makara), Saggitarius (Dhanusha), Aquarius (Kumbha), Pisces (Meena). Initially, these constellations were used to track the movement of the sun and determine the time during ancient times.

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Zodiac Signs and Constellations

The 12 zodiac signs listed in the horoscope closely determine the movement of the Earth through the heavens. The zodiac signs are derived from the constellations, which carve out the sun’s path through the universe. It’s not like that sun passes through some constellations at a particular date or time of the year, as many people believe. 

A closer observation of the Earth, the sun, and the stars reveal that the zodiac signs are more intricate than we think.

As Earth orbits around the sun, it appears like the sun is passing through different constellations. As the moon appears in a different position on the sky every night, the position of the sun also drifts towards the east with relative to distant stars. The sun doesn’t actually move. It appears to be moving due to the movement of the Earth around the sun.

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Constellations and Constellation of Stars

Sometimes, we might have looked up in the sky at night and lost within the stars’ wonders. You may also have heard about the constellations, but don’t know how to identify the constellations by yourself. 

You shouldn’t worry because with some simple orientation and little knowledge about the constellations; you can easily identify the constellations which commonly appear in the night sky.

a. Big Dipper/Ursa Major, ‘The Great Bear’

Big Dipper of the great bear is not actually a constellation, but it is a part of the constellation called Ursa Major. The Big Dipper is usually identified in a pattern of stars of the Northern Hemisphere, and hence it is an excellent starting point to begin the search of constellations.

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b. Little Dipper, ‘The Little Bear’ (Ursa Minor) 

Little Dipper can be spotted by the constellation of Big Dipper. If you look at the two stars which form the right part of the cup and follow the north’s straight line, it will lead you to Polaris, the North Star. Polaris is located at the end of Little Dipper’s handle, which is actually the Little Bear’s cup & tail forms part of the bear’s side part.

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c. Orion, ‘The Hunter’

It is the easiest constellation to spot in the night sky. Search for three bright stars that form the straight line of the hunter’s belt. If you have recognized it, you can easily locate Betelgeuse, the bright star that forms the hunter’s armpit, and towards the east, you can locate the hunter’s arm holding a bow.

d. Taurus, ‘The Bull’

Taurus “The Bull’ is easy to locate if you have found the Orion constellation. Taurus is located just above Orion constellation. You can easily locate Taurus if you find the large red star, Aldebaran, which lies near the folk of bull’s horn. 

The bottom horn is a part of the Crab Nebula. The Pleiades is a famous star cluster located above the bull. These clusters are lovely and can be seen with the naked eyes.

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e. Gemini, ‘The Twins’

Orion is also the key to locate the Gemini constellation. The twins can be found above one of the sides of the hunter’s raised arm. The constellation resembles two stick figure twins with touching outstretched arms. Start by locating two bright stars of the twins. The rest of the parts are simple to track. Both twins have heads, torsos, and legs. The left twin appears to lift one leg, perhaps like a small jig.

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Our Sun is surrounded by an atmosphere, which is a layer of gases. The corona is the Sun’s atmosphere’s outermost layer. The brilliant brightness of the Sun’s surface frequently obscures the corona. This makes it impossible to see without the use of specialised equipment. The corona, on the other hand, may be observed during a total solar eclipse. The moon passes between the Earth and the Sun during a complete solar eclipse. When this occurs, the moon conceals the Sun’s strong brightness. The eclipsed Sun is then surrounded by a dazzling white corona. In this post, we’ll look at what coronal meaning is, how solar eclipses affect the corona and solar wind.

Corona of Sun

The corona is the outermost portion of the Sun’s atmosphere, made mostly of plasma (hot ionised gas). It has a temperature of around two million kelvins and a very low density. As a result of the Sun’s magnetic field, the corona’s size and form change all the time. The solar wind, which sweeps radially outward through the whole solar system, is created by coronal gas expansion and only reaches the heliopause. Despite its high temperature, the corona generates very little heat due to its low density; that is, the component gas molecules are so sparse that the energy content per cubic centimetre is significantly less than that of the Sun’s core.

The corona radiates only about half as brilliantly as the Moon and is generally invisible to the naked eye due to the brilliance of the solar surface. During a total solar eclipse, the Moon blocks out the light from the photosphere, allowing for naked-eye observations of the corona and this is one of the major effects of solar eclipse on corona. The corona may also be observed under non-eclipse conditions using a coronagraph, which is a specialised telescopic equipment.

Reason for the Hotness of the Corona of the Sun

The high temperatures of the corona are a bit of a mystery. Assume you’re sitting close to a bonfire. It’s comfortable and toasty. However, as you move away from the fire, you feel a lot better. This appears to be the reverse of what appears to occur on the Sun. For a long time, astronomers have been attempting to answer this puzzle. The corona is located in the Sun’s outer atmosphere, far from its surface. The corona, on the other hand, is hundreds of times hotter than the Sun’s surface.

One conceivable solution might have come from a NASA project named IRIS. The expedition detected “heat bombs,” which are packets of extremely hot material that flow from the Sun into the corona. The heat bombs burst in the corona, releasing their energy as heat. However, scientists believe that this is merely one of several ways in which the corona is heated.

Solar Wind

The solar wind is a stream of particles that flows throughout the solar system at roughly one million miles per hour after leaving the sun. The solar wind, initially proposed by University of Chicago professor Eugene Parker in the 1950s, is visible in the halo encircling the sun during an eclipse and, on rare occasions, when the particles collide with the Earth’s atmosphere, resulting in the aurora borealis, or northern lights. While the solar wind protects Earth from potentially harmful space particles, storms may also damage our satellite and communications networks.

The Sun, like all stars, loses material by a stellar wind. Stellar winds are fast-moving material flows that are ejected from stars (protons, electrons, and atoms of heavier metals). These winds are distinguished by a continuous outflow of material flowing at velocities ranging from 20 to 2,000 km/sec. In the case of the Sun, wind speeds range from 200 to 300 km/sec in tranquil parts to 700 km/sec in coronal holes and active regions.

Stellar winds have different sources, ejection rates, and velocity depending on the mass of the star. The extraordinarily high temperature (millions of degrees Kelvin) of the corona causes the wind in comparatively cold, low-mass stars like the Sun. This high temperature is thought to be the result of magnetic field interactions at the star’s surface, giving enough energy for coronal gas to escape the star’s gravitational pull as a wind.

Although stars of this sort release a small proportion of their mass as a stellar wind each year (for example, only 1 part in 1014 of the Sun’s mass is ejected in this fashion each year), this nevertheless implies material losses of millions of tonnes each second. Stars like our Sun lose only a fraction of a percent of their mass through stellar winds during their entire lifespan.

When the solar wind interacts with the Earth’s upper atmosphere and magnetic field, it produces a variety of phenomena, the most visible of which are the aurorae (Borealis and Australis). These are formed when solar wind particles propelled by the Earth’s magnetic field clash with upper-atmosphere atoms and molecules. Light at specific wavelengths is emitted as atoms and molecules de-excite. A similar effect may be witnessed at Jupiter’s magnetic poles.

Have you ever wondered what current density is and how you can determine it? Before you can understand the current density formula, you must possess proper knowledge of current itself.

Defining Current

Current is the flow of electrons from an electrically abundant source to an electrically deficit destination. We use the symbol I to denote current, whereas ampere is the standard unit for measuring the same. 

Current always follows in a specific direction of flow. Thus, you will find current flowing from a positive to a negative point. 

What are AC and DC Current?

Before proceeding to learn what current density is, you should also be able to point out the differences between the two types of current – direct (DC) and alternating (AC). 

  

Current Density Definition

Current density is referred to as the total amount of current which is flowing through one unit value of a cross-sectional area. If this is of uniform current flow, then the amount of current which is flowing through a specific conductor is the same at all points of the conductor, even if the conductor area differs.

Current density formula can help to determine the amount of current in a specific portion of the conductor. 

What is the Current Density Formula?

Current Density (J) = I/A

In this equation, ‘I’ is the amount of current in Amperes while ‘A’ is the cross-section area in sq. meters.  

Current Density Example

Now that you are aware of the formula for calculation, take a look at the example below to get a clearer idea. 

Example – A 10mm2 of copper wire conducts a current flow of 2mA. Determine this current density using the current density formula.

Solution – In this example, current (I) = 2 x 10-3 

A = 10 x 10-3

Thus, current density (J) = 2 x 10-3/10 x 10-3

J = 0.20 A/m2

What is the Unit of Current Density?

The SI unit of current density is Ampere/meter2. This unit also helps you remember the formula for calculation of such a density. Since Ampere is the unit of current and meter2 is the unit for measuring cross-sectional area, one can easily derive the formula for current density. It is the current flow divided by the area of the cross section.

Quick Exercise – 1

What is this density when 137 Ampere of current flows through a conductor cross-section, measuring 1.2m2?

Solution – 

Here I = 137A

A = 1.2m2

Therefore, J = I/A

=> J = 137/1.2

=> J = 114.66 A/m2

What is the Relation between Current Density and Electric Field?

With the help of Ohm’s Law, you can determine a connection between electric field and current density.

We know I = nEavd

I = nAe(eE/m)

We know J = I/A

Now, I/A = ne2(E/m)

This is why charge density is so crucial in Physics. It relates to the electric field in electromagnetism. 

True or False

Q. Unit of measuring frequency for alternating current is Joule.

Ans. False. The unit for measuring the frequencies of AC is Hertz and not Joule. 

To form a better understanding of such concepts like density, Ohm’s law and more, join our online classes. Conducted by experts, each class looks to clear doubts for students. Now you can even download our app for convenient access to these online classes and study material on every topic.