Category: Physics Notes PPT

The ends of the magnet are known as the poles of the magnets. One side end is known as the North Pole and the other side of the magnet is known as the South Pole. If we take two magnets and one magnet’s south side is kept within distance of the north side of another magnet, then both will get attached. This property is known as the property of attraction. And if we place the magnets in the same direction, then both will become apart from each other. This property of magnet is known as the property of repulsion. We can conclude from this that opposite poles attract each other while similar does repulsion.

Magnetic Field Lines

The influence of magnetic forces in a region is described by magnetic field lines. It’s a visual used to depict and understand magnetic field lines. At a regional position  they describe the direction of magnetic fields in monopoles.

Though monopoles do not exist in nature so we describe field lines using different methods. One of them is the close connection between both the monopoles of the magnets and electric charges. Few conventions which we have adopted regarding the field lines are: that the field lines enter from the South Pole and get out from the North Pole of the magnet.

In principle, every position at the space field lines can be calculated. But in the visual medium it’s hard to represent. Therefore to indicate the field strength we use density of field lines. 

Monopoles: theoretical objects which have either north or south poles are known as the monopoles. Another way to analyse these poles are by magnetic charges, analogous to protons and electrons. As their existence is disputed so they can be artificially synthesized. It should be noted that electrostatic phenomenon is reduced by monopoles. The field lines converge at the south pole and emerge out of north poles.

Properties of Magnetic Field Lines

Magnetic field lines depict the direction of magnetic force. Discussing some of the properties of magnetic field lines. Magnetic field lines always form closed loops. These field lines originate from the north pole and end at the south pole by convention. The direction inside the magnet inversely appears to move from south pole to north of a bar magnet. The field lines move or bulge out when it’s moving from an area of higher permeability to an area of low permeability. Each of these lines contain the same strength. They never cross each other.

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Direction of Magnetic Field Lines 

Magnetic field lines are the lines which show the direction of magnetic force. 

In a bar magnet if there are two poles one designated as the north and the other as the south, the magnetic field lines make a loop and enter from the south and get outside from the north direction. In a monopole magnet the field line emerges from the north pole and converges in the south pole. If we isolate monopoles magnets in nature they will undergo similar interactions which are in an electric field. The electric field of charges and magnetic fields of monopoles will behave in a similar manner and a similar electric field would be observed in magnetic monopoles. The elegance of this idea  exists no matter whether poles exist or not.

Coulomb type law is seen when one claims the definition of magnetic charge  analogous to electric charge.

North and South Poles

A magnet consists of two poles of magnets which are designated as the south pole and the north pole. There are many magnets but primarily we will discuss the bar magnets. What we have observed above are the two poles of the magnets north and south poles. If we freely suspend a magnet it will always point out in the north direction. This property is known as the north pole of magnet.

Just opposite to the north lies the south end or south pole. If we see a compass which is itself a magnet and it always points in the north direction, except in the case of a strong magnet. In that case the pointing of the compass is different . The magnet field causes magnetic force which further causes attraction or repulsion. 

On the earth’s northern hemisphere the north magnetic pole is the wandering point at which earth’s magnetic field points downwards. 

This is the reason why the compass needle points in the north direction when freely suspended. But as we move towards the north magnetic pole it will point horizontally or in a straight direction.

According to the flux lobe elongation and magnetic flux the north magnetic poles move. Its counterpart south is in the south magnetic pole. The north and south poles are not antipodal as our earth is not symmetrical.

The human eye with its various parts and the roles which it plays are very important in our lives. Here, we are going to discover some of these roles, one of them is that it helps us to see. This may generally seem to us as a very simple process to just say it like that, but a series of operations occur from the point of light rays which is entering our eyes till we perceive the image of whatever we are seeing. One of these processes which we will see here is the power of accommodation of the eye.

What is Power of Accommodation of Eye?

The process by which certain muscles which are called ciliary muscles function to change the focal length of the eyes so that the image is clearly formed on the retina is known as the accommodation of the eye. This will vary for near objects and the ones which are distant and also for objects which are moving away or towards the eye. By adjusting the focal length, the eye is actually changing its lens power as well. So we can say that this is known as the accommodating power of the eye. The human eye has the power to change its accommodation.

We will now understand this with an example.

Keep a finger in front of you. Now you can see our finger try to focus only on the finger. 

You will notice that objects which are kept in the background tend to get blurry. 

Now we need to do the opposite. 

That is we need to keep our finger in front of our face but focus on something in the background. What happens now? Our finger is now seen as blurred.

So how does this accommodating power work? Considering varying distances we can ask this question.

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The answer is that if the object which we have kept for the experiment in consideration is at a distance for the image to form at the retina, that is,  the focal length has to be large. Here we will see that the ciliary muscles generally tend to relax thereby thinning the eye lens. The focal length which we are aware of will increase and the image is formed perfectly on the retina. 

Similarly, we can say that in the case of near lying objects the ciliary muscles contract and thereby thicken the lens. This causes a reduction in the focal length for ideal image formation.

Theories in Power of Accommodation 

• In 1855 the theory of Helmholtz — was the most widely held theory. It was proposed by Hermann von Helmholtz. It stated that while viewing a faraway object, the circularly arranged ciliary muscles relax allowing the lens zonules and suspensory ligaments to pull on the lens flattening it as well. The source which we are talking about is the tension and the pressure that the vitreous and aqueous humour exert outwards onto the sclera. On the other hand, while viewing a near object, the ciliary muscles contract, resisting the outward pressure on the sclera which causes the lens zonules to slacken which allows the lens to spring back into a thicker more convex form.

• In 1992 the theory of Schachar Ronald proposed what has been a bizarre geometric theory. It claims that the focus of the human lens is said to be associated with increased tension on the lens via the equatorial zonules.  When the ciliary muscles contract then the equatorial zonular tension is increased causing the central surfaces of the crystalline lens in nature to steepen the central thickness of the lens to increase and its anterior-posterior diameter and the peripheral surfaces of the lens to flatten. The tension on equatorial zonules is said to be increased during the accommodation process that is the anterior and posterior zonules are simultaneously relaxing.

What are Gases?

We say that gas is a state of matter and categorize it into the third category. Gas doesn’t have any shape, size, color, definite volume. So, wherever we place it, it takes the shape of that very container. 

The above statement signifies that a gas cannot acquire a definite shape and volume by itself, it always requires a medium to acquire these properties. 

There are other properties of gas like temperature, viscosity, volume, weight, entropy, and much more about which we will discuss in this article. 

What are the Properties of Gases?

In the above context, we already discussed that gasses do not possess any definite size, shape, and volume; they entirely occupy all the space accessible to them. 

The characteristic or properties of gases to fill the available volume within a container is because of the freedom that gas particles bear as they can randomly move in the accessible space. 

This determination of movement of gaseous molecules is because of the very weak binding forces among the molecules. In other words, their intermolecular force of attraction is very weak. Because of this, the molecules of a gas are in a continuous motion or we can say a Brownian motion. The below diagram shows the Brownian motion of gas molecules inside the container:

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The motion of gas from one place to another is related to the velocity of gas molecules. So, the higher is the velocity, greater will be the kinetic energy of gas molecules, which in turn, means a quick flow of gas, as we observe in the PNG gas pipeline system in our kitchens. There are many properties of gases; let’s discuss these one-by-one:

Properties of Gases

We say that when gases are compressed, they turn into a liquid state and this fact is true. We can see this in the below figure:

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The compression happens in a way that the molecules set apart in gases come close together and this, in turn, generates a good amount of interatomic force of attraction between these molecules, which is quite similar to the scenario of the molecular spacing and interaction, we observe in liquids.

We often use the term “compressibility” in the field of thermodynamics to describe the deviance in the thermodynamic properties of a real gas from those desired from an ideal gas. We define the compressibility factor with the following equation:

Z = PV/RT

Where,

Z = compressibility

P = Pressure inside the gas molecules

V = Volume of gas

T = Temperature in Kelvin

R = Universal gas constant 

We hear that the entropy of surroundings keeps on increasing and this fact is very true. If we talk about gases, on rising temperature, the molecules gain super kinetic energy because of which they start colliding with each other and with the walls of the container. 

However, on the other hand, if we decrease the temperature, the molecules come closer together and the volume of the gas increases with the decrease in its pressure. It can be explained by Boyle’s law, which is given by:

P α [frac{1}{v}] 

Also, temperature is the greatest factor in the kinetic theory of gases. 

On rising the pressure, the volume of the gas decreases, as we can see in the pipeline gas system, the gas is passed through the pipe with high pressure. Now, if we increase the temperature, the molecules of this gas gain kinetic energy and because of this, we get a faster supply of gas.

So, pressure and temperature vary inversely with each other and this relationship was explained by Charle’s law, which is as follows:

V α T

The molecules of the gas remain in perpetual or continual motion which means at a very high velocity.

There is a large amount of intermolecular space amid the gas molecules. When two gases are mixed, particles of one gas can effortlessly pass through the intermolecular space of the other gas, which is known as diffusion, and this property of a gas is called diffusibility. As an outcome both the gases get consistently and entirely mixed. Thus, a mixture of gases at all times remains homogeneous, which is a great feature of diffusibility in gases.

As we know that gases have large intermolecular spaces between molecules, they have very large volumes when compared to the mass of the gas. Therefore, gases have fewer densities. 

Let’s suppose that 2 ml of water at 78.4 ⁰F is converted into steam at 424 ⁰F and 2-atmosphere pressure or ‘2 atm’, it occupies a volume of 3400 ml.

• The Exertion of Pressure on Gas

As solids exert pressure only in the downward direction liquids apply pressure downward as well as to the sides but gases apply pressure in all directions. 

A good example is a balloon when we fill the gas inside it, it expands completely. This pressure is because of the breakdown of the particles against the walls of the vessel it is placed in.

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Physical Properties of gas include its color and odor.

Before moving into nuclear physics, students should note that matter is made up of particles called Electrons, Protons, and Neutrons. However, the fundamental or primary constituent of this matter is called quark.  Several quarks combine to form composite particles, also known as hadrons.  The protons and neutrons are also known as hadrons. Protons and neutrons are known as the constituents of matter and components of the atomic nucleus. 

Quark is the simplest part of a particle to date. It is the elementary particle that makes up the entire matter surrounding us. Quark is denoted by the letter “q”. 

 

Few of the Crucial Aspects of Quark Particle 

 

Example of Quark 

As per quark physics definition, it is the most fundamental particle present inside matter. However, they cannot have an independent existence like protons or neutrons. Therefore, two or more quarks combine to form a composite particle called hadrons. 

Proton is a stable hadron that comprises one down quark and two up quarks. Furthermore, a neutron consists of one up quark and two down types of quark. These concepts will help you understand what quark is and how the standard theoretical model explaining quark also explains the presence of other elementary particles and other unobserved particles. 

Antiquark – The antiparticles of quarks are known as antiquark. They are similar to quarks in terms of lifetime and spin. However, they differ in terms of concerning charges from that of a quark. 

The Building Block of Matter – Matter is made up of two kinds of fundamental particles 

1. Quark 

2. Leptons 

Both are segregated into six different types, thereby, 12 different types of particles are responsible for forming matter. 

 

Types of Quarks

There are six types of quark, among which up, down and strange are the primary types. These are also known as the flavour of quark. Knowing the properties will help you know what a quark is. 

• Up – These particles have the lowest mass and hence are the lightest. This is one of the reasons why these quark particles are most stable. It is represented as U and antiquark is expressed as U. The up quark mass ranges from 1.7 to 3.1 Me [frac{V}{C^{2}} ], and quark charges are equal to [frac{2}{3} e]. 

• Down – These particles have low mass followed by up quark and hence are highly stable. It is represented as d and antiquark is described as d. The down quark mass ranges from 4.1 to 5.7 Me [frac{V}{C^{2}}] and its electric charge is equal to [frac{-1}{3} e].

• Strange – This is the third-largest quark amongst the six. Strange Quark is represented as S and antiquark is represented as S. The strange quark has an electric charge equal to [frac{-1}{3} e].

• Bottom – Bottom quark is represented as b and its subsequent antiquark are represented as b. The bottom quark mass approximates 4.1 Ge [frac{V}{C^{2}}], and the quark charge is equal to [frac{-1}{3} e]..

• Top – Top quark is represented as t and antiquark are represented as t. The quark mass is 172.9 +1.5 Ge [frac{V}{C^{2}}], and quark charges are equal to [frac{2}{3} e].

• Charm – It is represented by C and antiquark is denoted as C. The electric charge of the charm quark is equal to [frac{+2}{3} ].

On the other hand, leptons are another type of elemental material that makeup matter and are divided into 6 types known as an electron, electron neutrino, muon neutrino, muon, tau neutrino, and tau. 

 

Multiple-Choice Questions 

1. Name the Particle Which is Made up of 1 up Quark and 2 Down Quarks?

1. Electron 

2. Atom

3. Proton 

4. Tachyon 

5. Neutron

2. Name the Fundamental Particles Which Help Create Strong Force Between Quarks?

1. Leptons

2. Quarks

3. Photons

4. Gluons

5. All of the above 

Learn the fundamentals of quark by reading these notes. You will also be able to learn quark definition, its types, and related concepts with the help of our app. This can be especially helpful since you can access the study material at your convenience.

An electric device that converts alternating current (AC), which periodically reverses direction, to (DC) direct current, which flows in only one direction is known as a rectifier. The process of doing this is known as rectification as it straightens the direction of current . physically describing rectifiers, take a number of forms including diode and vacuum tubes, wet chemical cells, mercury arc valves, stocks of cotton and selenium oxide plates, semiconductor diode, silicon controlled rectifiers and other silicon based semiconductor switches.  rectifiers have many uses but more often they are seen serving as components of DC supply of power and high voltage direct current power transmission system.

Bridge Rectifier

An important part of electronic power supply is the bridge rectifier. Different types of electronic power circuits also require the DC power supply for powering the various electronic components available in AC mains supply. Rectifiers are also found in various wide variety of electronics, AC power devices like the home appliances, modulation process, motor controllers, welding applications etc.

A bridge rectifier is a converter of alternating current (AC) to direct current (DC) that rectifies main AC input to main DC output.  These rectifiers are used in power supply that provide necessary DC voltage for electronics devices or components. Bridge rectifiers are of different types: 

Single Phase and Three Phase Rectifier 

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The nature of supply is dependent on the single phase or three phase rectifiers. A single phase rectifier consists of four bodies for converting the AC current into DC. on the other hand a three phase rectifier uses six diodes, as presented by the figure. 

Uncontrolled Bridge Rectifier

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This rectifier uses diodes for rectifying the input. As the name shows that this diode is a unidirectional device so it allows the current to flow in one direction only. With this diode configuration in the rectifier it does not allow the power to vary depending on the load requirement. 

Controlled Bridge Rectifier

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This is called an AC/DC converter or rectifier instead of uncontrolled diode controlled solid state devices like SCR, IGBT are used to vary output power at varying voltage.

Full Wave Rectifier

It is one of the methods to improve the cycle of conversions. Two bodies are used in the full wave rectifiers one for each half of the cycle. Multiple winding transformers are used whose secondary winding is equally split into two halves with a common center taped connection. 

This configuration results in each diode conducting in turn when it’s anode terminal is positive with respect to the center of the transformer which is producing output during both half cycles, twice for the half rectifier so it’s 100% efficient. 

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Half Wave Rectifier

A rectifier converts AC current to DC. It is done with the help of a diode or group of diodes, but a half wave rectifier uses only one diode whereas a full wave uses multiple diodes. It is the simplest form of rectifier available. Its working is: when a standard waveform is passed through it only half of the AC waveforms remain. It only allows half cycle of AC voltage through and it blocks the other half cycle on the DC side. 

Only one diode is required to initial a half wave cycle. As we know that the DC system is designed in such a manner that the current can flow in one direction only, putting a waveform from negative and positive cycles through a DC device may result in destructive consequences. So we use the half wave rectifier to convert the AC input to the DC output. 

The complete half circuit consists of three main components that are:

A transformer, resistive load, diode. 

Some Applications of Rectifiers

The primary use of a rectifier is to derive DC power from an AC supply. Inside the power supplies of the virtually electronic equipment. DCAC power supplies are divided into two parts that are linear power supply and switch mode power supplies. The rectifier in such power supply will be in series following the transformer and be filled by a smoothing filter and a voltage regulator. From one volt converting the DC power into another is much more complicated. DC-to-DC first converts power to AC then to change a voltage used by the transformer. And finally rectifies power back to DC. 

For the detection of amplitude modulated radio signals also rectifiers are used. The signal may get amplified before detection. 

Polarised voltage is supplied by rectifiers for welding purposes; in such circuits the output current is controlled, this is achieved sometimes by replacing the diode in a bridge rectifier with thyristors, diodes whose voltage output can be regulated.

Let’s suppose that you are climbing high mountains and your friend is observing you and climbing the small mountains. Here, your friend took time and could not complete the climbing task, while you were able to complete your journey, as the height was less, so it was enough energy that you had to accomplish the task. Here, you both had to cover the same distance; however, the amplitude of your friend was high, but the frequency was low, while in your case, it was just the reverse.  So, there is an inverse relationship between amplitude and frequency.

Amplitude and Frequency 

Do you know what amplitude is? Well! Amplitude is something similar to the height of a string that is hurled while skipping. Whenever the height is greater, we can say that is the amplitude of that instant hurl. Similarly, when you and your partner keep on hurling the string, the more complete waves, i.e., a crest and a trough are made, the higher is the frequency. Definition of amplitude: We define the amplitude of a periodic variable is a measure of its change/variation in a given period such as time or spatial period. There is another definition and that is the phase of a periodic function.

Definition of frequency: We define frequency as the number of occurrences of a repeating event in a unit of time. We often refer to frequency as temporal frequency, which emphasizes the contrast between spatial frequency and angular frequency. We measure the frequency in Hertz, which is symbolized as Hz. Hertz is defined as one occurrence of a repeating event per second, where the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency and its unit is seconds or s.

Amplitude Formula

The following formula is used to compute amplitude:

x = A sin(ωt+ϕ)

Where,

• x = displacement of the wave, in metres.

• A = amplitude of the wave, in metres.

• ω = angular frequency of the wave, in radians.

• t = time, in seconds.

• ϕ = phase shift, in radians.

Importance of Frequency 

For example, if a newborn baby girl’s heart beats at a frequency of 180 times a minute (3 hertz), its period, T, i.e., the time interval between beats, i.e., is one-third a second (60 seconds divided by 180 beats). We consider frequency as a significant parameter/function of time that is used in science and engineering to specify/understand the rate of oscillatory and vibratory phenomena such as mechanical vibrations, audio signals or a sound, radio waves, and light, etc.

Difference Between Amplitude and Frequency 

Amplitude- Amplitude is also a very important concept in periodic motion. To understand this we need to have a crystal clear understanding of harmonic motions. A simple harmonic motion or SHM is a motion that describes the relationship between the displacement and the velocity in the form of a = -2x, where “is the angular velocity and “x” is the displacement. 

Acceleration and displacement are nonparallel, which means that the net force on the object is also in the direction of the acceleration. This relationship describes a motion where the object oscillates about a central point. We know that when the displacement is zero the net force on the object is also zero, and this is the equilibrium point of the oscillation. We also know that the maximum displacement of the object from its equilibrium point is known as the amplitude of the oscillation. The amplitude of a simple harmonic oscillation entirely relies on the total mechanical energy of the system. 

For a spring-mass system, the total internal energy is E, the amplitude is equal to 2E/k, where k is the spring constant/force constant of the spring. At this amplitude, the instantaneous velocity is zero; hence, the kinetic energy is also zero, which means the total energy of the system is in the form of potential energy.; however, at the equilibrium point, the potential energy becomes zero.

Frequency- Frequency is a concept that is discussed in the periodic motions of objects. To understand the logic behind the term frequency, a proper understanding of periodic motions is required. A periodic motion is a motion that repeats itself in a fixed period. For example,

• A planet orbiting around the sun is in periodic motion.

• A satellite revolving around the earth is a periodic motion.

• The movement or the motion of a balanced football set is a periodic motion.

 

We must note that most of the periodic motions that we encounter are circular, linear or semi-circular. A periodic motion has a frequency. The frequency means how “frequent” the event is or how often an event occurs. For our understanding, we take frequency as the events per second; however, periodic motions can either be uniform or non-uniform. 

Amplitude and Frequency Relation

In the above context, we understood the amplitude and frequency relationship. A uniform motion can have a uniform angular velocity. Functions such as amplitude modulation or AM can have double periods; they are periodic functions encapsulated/hidden in other periodic functions. The inverse of the frequency of the periodic motion gives time for seconds. Simple harmonic motions and damped harmonic motions; are also considered periodic motions. Since the frequency of a periodic motion can also be obtained using the time difference between two similar occurrences/events. The frequency of a simple pendulum only depends on the length of the pendulum and the gravitational acceleration for small oscillations (vibrations).

Amplitude of Sound

We can hear sound because it is a kind of energy. When you ring a bell, it makes a sound. The vibrations may be felt if you touch the bell. The bell is ringing, as you can see. The bell’s to-and-fro motion is referred to as vibration. A sound wave’s amplitude is a measure of the wave’s height. The largest displacement of vibrating particles of the medium from their mean location at the moment the sound is emitted may be characterized as the loudness of a sound wave. It is the distance between the crest or trough of a wave and its mean position. The loudness of a sound is related to its amplitu
de. The amplitude of a sound wave enhances the loudness of the sound. If the amplitude is little, the sound will be weak. The greatest displacement of a sound wave from its equilibrium location is defined as its amplitude. It’s also known as the loudness of a sound after it’s been created.

The sine wave is given by the equation:

y = A sin ω t

Where,

A = amplitude of the wave,

ω = angular frequency of the wave,

t = period of one oscillation.

Depending on how the wave oscillates, the amplitude will fluctuate. A sound wave’s amplitude and loudness are proportional. The sound will be louder if the amplitude is greater. The sound generated will be smaller if the amplitude is little.

Frequency of Sound

A sound pressure wave’s frequency is the number of times it repeats itself per second. The frequency of a drumbeat is significantly lower than that of a whistle, while the frequency of a bullfrog cry is much lower than that of a cricket. The fewer the oscillations, the lower the frequency. Oscillations are more common at higher frequencies. The frequency units are called hertz (Hz).  Sounds between 20 Hz and 20,000 Hz can be heard by those with normal hearing. Ultrasound is defined as frequencies greater than 20,000 Hz.

Effect of frequency and amplitude on sound

Does Amplitude affect Frequency?

The relationship between the wave’s amplitude and frequency is such that it is inversely proportional to the frequency. The amplitude decreases as the frequency increases. The amplitude increases as the frequency decreases.