Category: Physics Notes PPT

What is Convection?

Convection is the process of heat transfer in which transfer of heat energy occurs by the mass movement of molecules of the fluids like gases and liquids. Gases and liquids are not a good conductor of heat under normal conditions, but they can easily transfer heat.

Heat transfer through convection occurs other through diffusion or advection or both. Convection does not take place in solids, because no movement of its constituent particles occurs. The diffusion of heat occurs in solids, and it is called thermal conduction.

The process in which heat transfer occurs between a surface and a liquid or a fluid that is in contact with the surface is called convection heat transfer. Convection plays a major role while transferring heat from one liquid to another liquid through a barrier. Heat transfer by convection either occurs due to thermal diffusion (motion of fluid molecule) or advection, in which heat is transferred by the bulk motion of heat currents in the fluid.

Newton’s Law of Cooling

Under normal conditions, the heat transfer due to convection is directly proportional to the temperature difference between the parts. Newton’s law of cooling has expressed this phenomenon, and the law states that:

The heat transfer rate of a body due to convection is directly proportional to the temperature difference between the body and its surroundings. The temperature difference should be small, and the nature of the radiating surface remains the same. This is the convection heat transfer equation:

P = [frac{{dq }}{dt}] = hA(T – T₀)

Where

P = [frac{{dq }}{dt}] is the rate of heat transfer

h is the coefficient of the convection heat transfer

A is the surface area of the body

T is the temperature of the object

T0 is the temperature of the fluid or liquid which is subjected to convection

Heat-transfer coefficient h depends on the following factors:

Density, Thermal conductivity, Viscosity, coefficient of convective heat transfer, and specific heat capacity

The constant of proportionality mentioned in the above formula is an important parameter and is called a coefficient of convective heat transfer ‘h’. It is defined as:

The rate at which heat transfer occurs between a solid and a fluid part per unit surface area and for the unit temperature difference:

𝒉 = [frac{{q}}{ΔT}] 

Where

q is the local heat flux density [W.m^-2]

H is the heat transfer coefficient [W.m^-2.K]

ΔT is the temperature difference [K]

The horizon is a visible line that separates all viewing lines depending on whether or not it intersects the Earth’s surface. The study of the horizon is called horizon astronomy. The horizon definition in astronomy is defined as, the particular line, which can only be observed when it lies on the sea surface. 

When looking at a sea from a seaside, then the part of the sea nearest to the horizon is called the offing. This line is obscured by terrain, towers, trees, houses, and mountains in many places, and the resultant convergence of earth and sky is referred to as the apparent horizon in astronomy.

The true horizon definition astronomy near the observer is generally assumed to be a circle, drawn on the surface of a spherical model of the Earth. 

The horizon centre is under the observer and below sea level. Its distance from the observer differs from day to day due to atmospheric refraction, which is seriously affected by weather conditions. 

Also, the horizon is far away from the observer, the higher the observer’s eyes are from sea level. For example, in standard atmosphere conditions, for an observer with eye-level above the sea level by 2 metres, the horizon is at a distance of about 6 kilometres. 

Types of Horizon

When it is observed from high standpoints, like as a space station, then the horizon is far away and it surrounds a much larger area of Earth’s surface. In this case, the horizon would no longer be an exact circle, not even a plane curve like an ellipse. Especially when the observer is above the equator, as the Earth’s surface can be much better modelled as an ellipsoid than as a sphere.

There are two main types of horizons

1)  Earth-sky horizons 

2) Celestial horizons. 

There are subtypes of earth-sky horizons and celestial horizons. The Local horizons, sea-level horizons and geographic horizons are the sub-parts of Earth-sky horizons.

While, the astronomical and true horizons are celestial horizons. 

Earth-Sky Horizons 

The local horizon is the visible boundary between the Earth and the sky. The local horizon includes trees, buildings, and mountains. The geographic horizon is the visible boundary between the Earth and the sky. Mountains, trees, buildings, and other elevated features are not considered part of the geographic horizon.

 

The spatial horizon is the same as the sea-level horizon, but only at sea level. A beach is one of the best ways to see the sea-level horizon where the Earth seems to touch the horizon, the ocean and sky have a clean, flat surface. If the observer is standing on the beach and looking out at the sea, the offing refers to the part of the sea that “touches” the horizon.

Celestial Horizons

Celestial horizons are used by astronomers, for the measurements of the position of the Earth relative to the rest of the sky. The celestial horizon is a flat passing from the earth’s centre perpendicular to the zenith-nadir axis. The visual horizon approaches this plane at the earth’s surface. 

The astronomy horizon is the type of celestial horizon whose imaginary horizontal plane is always at a 90-degree angle from the observer’s zenith. Celestial horizons are perfect circles that surround the observer. The true horizon is the theoretical plane that passes through the centre of the Earth, its radius is perpendicular. From orbit, the true horizon is spherical, following the shape of the Earth. The altitude of a celestial body is calculated using the celestial horizon as a reference point. Celestial horizons are called rational horizon to compare sensible horizon. 

Important Points

1. The theory of the horizon is important to different types of work, including aviation, navigation, and art. 

2. The horizon is used by pilots to keep the plane level when in the air. This method is called “attitude flying,” Pilots can handle their aircraft by determining the relationship between the aircraft’s front end or the aircraft’s nose, and the horizon. By shifting the horizon to be mostly sky or mostly earth, pilots may adjust their altitude or flight pattern.

3. Before the explanation of the latest tools such as Global Positioning System (GPS) devices, sailors depended on a perfect view of the horizons to navigate the ocean.

4. The sun’s position to the horizon told sailors what time of day it was and what direction they were boat or crew.

5. You will see stars appearing on the eastern horizon astronomy (just as the Sun and Moon), spreading around the dome of the sky during the night, and settling on the western horizon if you lay down in an open field and watch the night sky for hours, as ancient shepherds and travellers did. 

6. In astronomy, the horizon is the point where the sky seems to touch the earth or the sea. (In astronomy it is called the intersection on the celestial horizon sphere of a plane perpendicular to a straight line). The higher the observer, the lower and more distant is his visible horizon in astronomy.

Event Horizon Astronomy

In astronomy, event horizon definition is a partition beyond which events cannot affect an observer. The term was discovered by Wolfgang Rindler.

The event horizon definition astronomy, is the circumstance defining the region of space around a black hole from which nothing can escape. And an object within the event horizon has a faster escape velocity than light. The name arises since it is impossible to observe any event taking place inside it is the horizon beyond which we cannot see. As a result, the event horizon essentially covers the singularity at the black hole’s core, which is a relief for astrophysicists concerned about the collapse in physics at such a point.

All singularities are obscured by an event horizon, according to the cosmic mind regulation hypothesis, and this violation of the laws of physics is not visible. In theory, mass can be compressed sufficiently to form a black hole. The only stipulation is that it must be less than the radius of the event horizon. For example, our Sun would become a black hole if its mass was contained within a sphere about 3 km across.

Have we ever wondered that whatever we want we get it by saying or expression. One of the best modes to express our feelings is by our voice. We can say that voice is one of the medium by which one recognises us as well.

The size that is of vocal cords generally affects the pitch of voice. This opens when there is a process of breathing and vibrating for speech or singing and then the folds are controlled via the recurrent laryngeal branch of the vagus nerve.

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Parts of Production of Voice 

The means of communication is said to be very  essential for the well-being of any animal and human as well. Even the organisms which are the microorganisms communicate with each other by means of chemicals.  Fortunately we can say that our means of communication are far better than that. So we rely on it every day to interact with others. As is the case with walking and seeing, taking as well. We can say that the human voice is very versatile and this is rich both incontent and  range. We generally use it to laugh and cry and scream as well as shout, sing and the list goes on. The human voice which is produced by the vocal cord is capable of producing highly sound intricate. We  can tell if our mother is angry at us by her voice. Some people do one better and can tell if people are lying that too just by their voice.

Following Are Said to Be the Main Parts of Production of Voice

• We can say that the power source: that is lungs.

• The  vibrator: that is the voice box.

• The resonator: that is the throat, mouth, nose and sinuses.

The Power Source: Which is Lungs

We can say that the lungs here perform the essential function of supplying adequate airflow and air pressure in order to vibrate the vocal cord. When we inhale the oxygen that is when we draw air into the lungs. This air is then later exhaled which is creating a stream of air that is through our wide throat and pipe. This is said to be very exciting that the air provides the energy to vibrate the vocal cords in the box or we say the voice box to produce sound. If we want to make a sound that is loud then we have to exhale hard to create a strong airflow.

• The Vibrator: The Voice Box

The part of the throat that generally moves when we swallow is called a voice box. The Voice Box that is the Larynx sits on the top of the wide pipe. The voice box is said to be a part of the wide pipe and the exhaled air which is from our lungs generally passes through the voice box. The vocal cord generally consists of two tight strings that open during breathing and later close when we exhale to make a sound. They vibrate very fast that is almost from 100 to 1000 times per second in terms. We may vary the pitch that is ‎which explains the concept of frequency and pitch etc by controlling the tension in the muscles that is present in the voice box. The vocal cord is generally also known as a fold that is the vocal fold. The vocal cord generally modulates the flow of air from the lungs.

• The Resonator: That Includes Throat and Nose and Mouth and Sinuses

The chords that are the vocal cords by themselves produce only a buzzing sound much like a bee. The sound is not usually created by vocal cords. Instead we can say that it is created by the interactions of the vibrations which are created by our vocal cord with the muscles and tissues which are present in your mouth, nose, throat and tongue. When we talk, our tongue generally darts all around our mouth which is helping us to pronounce complex syllables. The vibrations that are said to be deliberately altered in our throat and mouth to produce the unique voice of humans.

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Disorders of Voice

There are many disorders which affect the voice of humans. These usually include speech impediments and the growths and lesions on the folds of the vocal box. We are talking improperly for long periods of time causing vocal loading which is stress inflicted on the organ of speech. When vocal injury is done then often an specialist of the ENT may be able to help but we can say that the best treatment is said to be the prevention of injuries through good vocal production. The therapy of voice is generally said to be delivered by a speech-language pathologist.

The nodules which are the vocal are generally caused over time by repeated abuse of the vocal cords which results in soft and then the swollen spots on each vocal cord. These spots which usually develop into harder that is the callous-like growths known as the nodules. The longer and the abuse generally occurs the larger and stiffer the nodules will become.  We can say that most polyps are larger than nodules and may be known by other names such as polypoid degeneration or the Reinke’s edema. The polyps are said to be caused by a single occurrence and may require removal from surgery. The irritation which occurred after the removal may then lead to nodules if additional irritation persists for a longer time.  The hoarseness or the breathiness that lasts for more than two weeks is a symptom that is common of an underlying disorder of the voice such as nodes or polyps and should be investigated medically.

In physics, impedance of free space, also recognized as the characteristic impedance of free space, is a physical constant signified by Z0. This narrates the magnitude of the magnetic field and the electric field of electromagnetic radiation roaming through free space.

The impedance of free space (means the wave impedance of a simple wave in free space) is equal to the multiplication of the speed of light in vacuum c0 and the vacuum permeability μ0.

Before 2019, the magnitudes of both these constants were considered to be precise (they were arranged in the descriptions of the ampere and the meter respectively), and the rate of the impedance of free space was taken to be exact similarly. 

However, with the redefinition of SI base units that approached into force on 20 May 2019, the impedance of free space is a matter to experimental measurement because only the speed of light in vacuum recollects a correctly distinct value.

Value of Intrinsic Impedance of Free Space

It is explained as the square root of the proportion of permeability of free space to the permittivity of free space.

The particular value of the impedance of free space is universally acknowledged, and the elaborated value is-

The Impedance of free spaceZ₀ = 376.73Ω.

Intrinsic Impedance of Free Space Formula

The impedance of free space can be accurately inscribed as:

Z[_{0}] = [frac{E}{H}] = [mu _{0}]c[_{0}] = [sqrt{frac{mu _{0}}{c_{0}}}] = [frac{1}{varepsilon _{0}c_{0}}]

Where,

μ₀ is the magnetic constant

ε₀ is the electric constant

C₀ is called the speed of light in free space.

E is the electric field strength.

H is the magnetic field strength.

Z₀ sometimes also denoted the admission of free space.

Let’s hope that you have agreed with the Impedance of free space or the characteristic Impedance of free space alongside units, values, and the formulations.

Characteristics Impedance of Free Space

These are some answers start to appear as we consider these facts such as:

1. Characteristic impedance is a characteristic of any medium that can embrace the transmission of an electromagnetic wave irrespective of whether or not it is associated with a power source at one terminal and a load at the other end.

Characteristic impedance adjusts signal or the current passing through a conductor. But if there is no non-stationary energy at a certain point in time, that does not change the fact that the medium has a precise characteristic impedance. 

A reel of coax in the ware-house has similar characteristic impedance as when it is wired into an active, working network.

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2. Characteristic impedance, nothing like conventional impedance, is free of length or distance over which signals propagate. Consequently, the characteristic impedance of the universe is the equivalent of the characteristic impedance of a circuit navigating about 50 feet of free space.

3. The characteristic impedance of a vacuum is considered equivalent to that of dry air which has almost no effect on conductance.

4. The characteristic impedance of free space is equivalent to the sq root of the proportion of penetrability of free space (henrys per meter) to the penetrability of free space (farads per meter). It figures out about 377 Ω, and that is the characteristic impedance of the universe.

Impedance of Free Space Derivation

The impedance of free space also recognized as the characteristic impedance of free space is a physical constant represented by Z0 which co-relates the magnitude of the magnetic field and the electric field of electromagnetic radiation traveling through free space.

The wave impedance in free space of plane waves is illustrated by:

Z[_{0}] = [frac{E}{H}] = [mu _{0}]c[_{0}] = [sqrt{frac{mu _{0}}{c_{0}}}] = [frac{1}{varepsilon _{0}c_{0}}]

How to Make Notes on Impedance of Free Space

• Go through and click on Impedance of Free Space

• Read the page and then start writing down everything in your own language

• Follow the sequence of the page

• Mark all they key areas using some colour

• Write brief sentences

• Do not just copy-paste from the main page

• Revise from these before an exam

How Prepares Students for Impedance of Free Space in Physics

has Impedance of Free Space on its platform that helps it to understand the chapter. This material has been provided free of cost and is useful for all students to read from. The formulas and other subtopics have also been provided as per the student’s understanding. is India’s leading onlne tutoring platform that employs teachers from all over the country to write for its platform. It has the best of study material which has shaped the careers of multiple students and is instrumental in helping the students get placements in all the premier institutes.

Do You know?

Is there any characteristic impedance in the universe? If yes, then what is the value? 

The universe is collected of huge quantities of blank space between relatively small stars broadly spaced apart. It is believed that when our Milky Way and the Andromeda Galaxy encounter 4 billion years from now, not even one star from galaxies will truly strike. 

Scientists explain if stars were the size of balls like ping pong, they would be spread out on the order of two miles apart. However, there will undoubtedly be no collisions; both galaxies will be deeply exaggerated by the connections of their enormous gravitational fields.

Employing an electrical channel with characteristic impedance, the universe was possibly built with enhanced quality control than our best coaxial cable.

Let’s suppose that you and your friend plan out a day to meet at your favorite restaurant and as the time comes, you feel happy to meet each other. So, the meeting of you and your friend at commonplace is called interference in Physics. Interference Physics clearly says that when two waves coming from varying sources that are not necessarily coherent meet at a point, that point is exactly the interference.

Here, you will learn about interference, its types, its effect on two waves, and also its contrast with the diffraction of light.

In Physics, we can say that interference is a phenomenon in which two waves superpose to form a resultant wave of greater, lower, or the same amplitude. Both Constructive and destructive interference result from the interaction of waves that are correlated or coherent with each other because they come from the same source. The Interference effects can be observed with all types of waves. 

Interference Physics

Now that we know the meeting point of two friends or waves coming from different places or sources is called interference. Also, we know that friendship is unity. 

 

Now, add another scenario by supposing that you both are army men and some intruders with their superpower guns start firing in the restaurant. As for a single person, it becomes hard to fight these goons, so you both and other army men or policemen having their lunch unite or superimpose by fighting these goons together and protecting hundreds of lives.

 

So, here, the greater the number of brave people, the more people’s lives are saved at the restaurant. 

 

In Physics, the scenario is similar, the two waves superimpose on each other to give a wave of greater amplitude; let’s see how it happens by observing the following diagram.

 

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So, people find security under these bravos, and this situation talks about the constructive interference of light. This context could surely give you an idea that there are types of interference and about one is already discussed above. Now, let’s talk about the types of interference.

Types of Interference

There are two types of interference in Physics which are described as below:

This type of interference is  called constructive interference. Constructive interference is interference that occurs at any location along with the medium where the two interfering waves have a displacement in the same direction.

Both waves have an upward displacement as the  medium has an upward displacement that is greater than the displacement of the two interfering pulses. The constructive interference is observed mainly at  locations where the two interfering waves are displaced upward and also both interfering waves are displaced downward. 

Example

We join two or more bogies to get a big train and fetch maximum people to a particular location without needing to manufacture two or more trains for a single location and utilize a lump sum of money for the same.

Destructive interference occurs at any location along with the medium where the two interfering waves have a displacement in the opposite direction. When  a sine pulse with a maximum displacement of +1 unit meets a sine pulse with a maximum displacement of –1 unit, destructive interference occurs. 

Constructive Interference VS Destructive Interference 

So, we know that the waves making a big wave is constructive interference whereas two waves canceling each other is destructive interference. The difference between the two types of interference is described in the form of the following graph:

In this graph, we can see that the crest and troughs of the two waves overlap each other. The same scenario is observable when we drop a stone in water, the waves spread in the form of concentric circles, and the point of this overlap is the interference; this is for constructive interference.

 

Now, talking about the destructive interference, another stone is dropped in the vicinity of these already formed concentric circular waves. So, here, the waves of another stone may cancel out the already formed waves. Now, this canceling may produce no effect and that’s the point where we get the destructive interference.

Equation of Interference in Physics

Constructive Interference: When the phase difference is an even multiple of π (φ = ….., –4π, –2π, 0, 2π, 4π,……), then cos φ/2 =1, so the sum of the two waves is a wave with twice the amplitude.

 

W₁+W₂ = 2A cos(kx−ωt)W₁+W₂=2A cos (kx−ωt)

Destructive interference: When the phase difference is an odd multiple of π (φ =….., –3π, –π, 0, π, 3π, 5π,……), then cos φ/2 = 0, so the sum of the two waves will be zero.

W₁+W₂=0

Constructive Interference Equation

The equations for constructive interference are as follows:

           y₁ = Cos (kx – t), and

           y₂ = Cos [Cos (kx – t + frac {pi}{2})]

Here,

ω = Frequency in per Radians

k = wave number (= 1) 

δ = phase difference between two waves

t = time

x = wave position in a given time ‘t’

 

The frequency of two waves is the same as in constructive interference. We get the superimposed wave of the same amplitude and frequency. 

Point to Remember

In determining the interference of light, we use fringes, so in the pattern of interference, the intensity at minima is usually negligible or close to zero, which means minima is usually dark. 

 

Also, there is a very good contrast between the dark and bright fringe.

Interference and Diffraction of Light

Interference of Light

Interference of light takes place on the meeting of the two waves as they travel along with a similar medium. Besides this, the interference causes the medium to take a particular orientation; moreover, this shape is due to the whole effect of two individual waves on the medium’s particles.

 

Diffraction of Light

Diffraction is observable in the scenario of waves passing through an aperture spread out in the dark region like a light coming out of a tunnel. In the case of diffraction, the size of the obstacle or aperture is of straight dimensions to the incident wave’s wavelength, and its occurrence is significant. Furthermore, it takes place when the traveling wavelength’s part gets shaded.

The basic unit of mass in the current metric system and the International System of Units (SI) is the kilogram. Its unit symbol is kg. It is a widely used unit in the field of science, engineering, and commerce all across the globe, and it is often even called a kilo in everyday speech. A kilogram was originally defined in 1795 to be equal to the mass of a thousand cubic cm or one liter of water. One kilogram is said to be 2.2 times heavier than a pound. A pound is defined to be exactly equal to 0.45359237 kg.

The International System of Units

During the initial times, the Meter convention was just concerned with the units, kilogram, and meter, but the scope of the treaty extended in 1921 to accommodate all the physical measurements and thus all the aspects present in the metric system. In 1960, the 11th CGPM held in Paris approved the International System of Units.

Just as the initial formulation of the metric system had grown out of the confusions scientists came across in dealing with the medieval system, so a new system grew out of the problems an enormously large scientific community faced in the rapid growth of the subsystems improvised to serve certain disciplines. At the same time, it came to the notice of the people that the initial standards of the 18th century were not accurate to the degree demanded by the 20th-century operations so new definitions were required. In 1960 October, after a long discussion, the 11th General Conference on Weights and Measures in Paris defined a new International System of Units. Its abbreviation is SI. The base units for the following were adopted and defined accordingly:  

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

• Thermodynamic Temperature: kelvin (K)

• Electric Current: ampere (A)

• Light (luminous) Intensity: candela (cd) 

• Amount of Substance: mole (mol)

What is Kg?

As originally defined, the unit of mass kilogram was represented by a solid cylinder of platinum in the late 18th century. The measurement of the mass of the volume of water turned out to be pretty imprecise and inconvenient to be made, making the platinum artifact itself the standard. Later in 1889, it was replaced by a standard kilogram, also called a cylinder, of height equivalent to its diameter, made up of the exact same platinum-iridium alloy which was then used as the standard for determining the unit meter. The standard kilogram was kept in France, at the International Bureau of Weights and Measures at Sevres. However, in 1989 it finally came to notice that the sample kept at Sevres was 50 micrograms lighter than the other copies of the standard kilogram. To avoid the confusion of having the kilogram defined by an object of inconsistent mass, a proposal was agreed to begin to redefine the kilogram not by a physical artifact but by a fundamental physical constant in the year 2011 by the General Conference on Weights and Measures (CGPM). Planck’s constant was the constant that was chosen, which was to be defined as equal to 6.62607015 x 10-34 joule second. One kilogram times meter squared per second squared is said to be equal to one joule. 

Some SI Multiples of Mass

As SI prefixes are not concatenated within the name or symbol for a unit of measurement, SI prefixes are used with the unit of mass, gram, and not kilogram. This is because kilogram already has a prefix as a part of its name. For example, one-millionth of a kilogram is not 1 microgram, but 1 milligram.

Some Common Multiples of Gram are:

Some Common Facts on Certain Multiples of the Unit Gram are:

• The microgram is abbreviated as “mcg” and this unit is used in pharmaceutical and nutritional supplement labelling.

• Another very commonly used multiple of the unit gram is hectogram. It is used in the retail food trade in Italy. It is usually called etto which is a short form for ettogrammo which is the Italian for hectogram. 1 hectogram is equivalent to 100 g.

• The unit megagram is rarely used. For most purposes, the unit tonne is used. Its symbol is “t”. The unit megatonne is used in general-interest literature on greenhouse gas emissions. The equivalent unit found in science papers on the subject is often teragram (Tg).

• In the UK due to some serious medication errors which have occurred due to the confusion between milligrams and micrograms, microgram must be written in full and it is unacceptable to use “mcg” or “µg”.