Category: Physics Notes PPT

The magnetic field is a region or space where there is an influence of a magnet. There are different types of magnets. Bar magnets, rod magnets, horseshoe magnet, ring magnet etc. All types of magnets have two poles; North Pole which is indicated by ‘N’ and South Pole which is indicated by ‘S’. Irrespective of shape every magnet has a field around it. For a better understanding of the magnetic field, place an iron nail in a particular distance from the magnet. Suddenly it gets attracted towards the magnet. If the iron nail is far away from the magnet, it will not have any influence. The area where the power of the magnet exists is known as magnetic field or B field.

The magnetic field can be illustrated in two different ways; vector field and magnetic field lines.

Vector Field

Vector field is the mathematical description of the magnetic field. It is considered that the magnetic field has both magnitude and direction. The vector field can be drawn as a set of vectors drawn on a grid. The direction of each vector points in the direction of the compass. The length of the vector depends upon the strength of magnetic force. 

Magnetic Field Lines

Magnetic field lines are imaginary lines around the magnet. The magnitude of a field is indicated by its line’s density. Near the South and North Pole of a magnet, the magnetic field is stronger and will get weaker when it moves away from the poles. This concept can be clarified by doing a simple experiment. Fix a sheet of white paper on a table and place a bar magnet at the center. Sprinkle some iron filings around the magnet. Gently tap the table. It can be seen that the iron filings align themselves in a specific pattern which represents the field of that magnet. If these patterns are observed clearly, it can be seen that iron filings are accumulated near the poles, whereas concentration is less in the region away from the poles.

Magnetic Field Lines have various Properties:

1. The magnetic field lines never intersect each other.

2. It takes the least resistant path between the opposite magnetic poles. Path of magnetic lines of force of a bar magnet is closed loops from one pole to the other.

3. The length of magnetic field lines will be the same.

4. As the field lines move from higher permeability region to the lower permeability region, their density will decrease.

5. Within a material magnetic field, lines flow from south pole to the north pole and in the air, their direction of flow will be from north pole to south pole.

6. Density of the magnetic field depends upon the distance from the pole. As the distance from the pole increases, their density decreases.

7. The magnetic field is a vector quantity because it has both magnitude and direction.

How to draw Magnetic Field Lines?

Magnetic field lines can be drawn by using a compass, bar magnet and a chart paper. First, fix the paper on a drawing board. Place the bar magnet at the center and mark the position with a pencil. Keep the compass near any one pole of the magnet. Make sure that there is no other magnetic material nearby. It can be seen that the compass arrow is pointing in some directions. Mark a dot in that direction. Move the compass from that position and place it on the dot in such a way that the base of the arrow is at the dot. Mark a new dot in the direction where the arrow of the compass is pointing now.

Until the compass reaches the opposite pole of the magnet, repeat this procedure. Join the dots. Again come back to the previous position and repeat the same steps by starting from a new spot. After drawing a number of lines, it can be seen that the lines are forming a closed loop and this seems to start from one pole of the magnet and ends in another pole. This is the method to draw magnetic field lines. If these lines are compared with the alignment of iron filings, the similarity of the patterns can be noticed. Depending upon the type of magnets, magnetic field lines also will vary.

How is the Magnetic Field produced?

The magnetic field is not only produced by the magnet but also can be produced by a moving charge or electric currents. We all know that matter is made up of tiny particles called atoms. The nucleus of an atom consists of protons and neutrons, with electrons revolving around it. Spinning and orbiting of protons and neutrons or nucleus of an atom produce the magnetic field. The direction of the magnetic field is decided by the direction of orbit and spin. The magnetic field is mathematically represented by the symbol ‘B’. Its unit is Tesla (T). 

Earth’s Magnetic Field

Evidence of earth’s magnetic field was first given by Sir William Gilbert in the year 1600. Based on some experiments he found that earth shows some magnetic properties and it has a magnetic field. If a magnet is suspended freely from a thread and is allowed to rotate in a horizontal plane, it will align automatically in the north-south direction and come into rest. Alignment of the magnet will be in such a way that the north pole of the magnet is attracted towards the geographical south and south pole of the magnet is attracted towards the geographical north. 

The second evidence is that there are some neutral points in the magnetic field lines. Magnetic field due to the magnet, which is used to draw field lines, is canceled by the earth’s magnetic field. Without earth’s magnetic field these neutral points cannot be seen. Third evidence is that a soft iron becomes a magnet if it is buried under the earth in the north-south direction. 

 

The Hypothesis for the source of Earth’s Magnetic Field

1. The Earth’s core is in the form of hot molten liquid and it contains ions. These ions are circulating in the form of current loops inside the liquid and as a result, the magnetic field is produced.

2. The Earth is rotating about its axis and matter on the earth is made of charged particles. These charged particles also rotate about earth’s axis in the form of current loops and are responsible for the production of the magnetic field.

3. The Earth’s outer layer consists of ionized gasses. When the earth is rotating, movement of ions produces electric current and a magnetic field is produced due to this.

Characteristics of the Earth’s Magnetic Field

1. Earth’s magnetic field is uniform.

2. The magnetic field strength at the surface of the earth is approximately 10-4 Tesla

3. The magnetic field of the earth is extended up to a height of 5 times the radius of the earth.

 Applications of Magnets in Real Life

1. Magnets are used in electric bells.

2. They are used in the construction of generators and electrical motors.

3. Magnets are used to find the geographical directions.

4. Magnets play an important role in the separation of magnetic and non-magnetic materials from the scrap.

5. In the medical field also, magnets are widely used in treating pain of different body parts.

Operating the Magnetic Field

Each magnet has a field surrounding it, regardless of its shape. Put an iron nail at a certain distance from the magnet in order to obtain a better understanding of the magnetic field. At that moment, the nail becomes drawn to the magnet. The iron nail will not be able to exert any influence on the magnet if it is far away from it. The magnetic field that exists around magnets is called the B field.

The magnetic field is created by moving magnets or electric charges. Magnetism operates inside the magnetic field surrounding magnetic materials or moving charges. A magnetic field line represents a magnetic field. A visual tool that provides information about the direction and strength of the magnetic field.

The magnetic field lines can be drawn using a compass needle. It is recommended that the compass needle be placed near the magnet on a piece of paper. Check the direction of the compass needle and mark it. Move the compass needle to various positions and mark the directions. By joining the points, you can see the magnetic field lines.

Before we are going to start about “what is mmf”,magnetomotive force and its unit. First, we must have the knowledge regarding the magnetic circuit and various terms related to it like magnetic reluctance, magnetic flux etc. Therefore first we are going to study magnetic circuits. A magnetic field, shown as lines of magnetic flux, is restricted to a magnetic circuit, which is a closed channel. In contrast to an electric circuit, where electricity flows, a magnetic circuit has no electricity flowing through it. The magnetic field or flux in a ring-shaped electromagnet with a tiny air gap is nearly totally contained to the metal core and the air gap, which together form the magnetic circuit. 

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The magnetic field of an electric motor is restricted mostly to the magnetic pole pieces, the rotor, the air gaps between the rotor and the pole pieces, and the metal frame. Each magnetic field line forms an uninterrupted circle. The total flux is the sum of all the lines. The magnetic circuit is considered parallel when the flux is split so that part of it is limited to one section of the device and the other to another. A series magnetic circuit is formed when all of the flux is contained within a single closed loop, as in a ring-shaped electromagnet. The current, electromotive force (voltage), and resistance are all related by Ohm’s equation in a magnetic circuit, just as they are in an electric circuit.

What is MMF?

The electric current is equivalent to the magnetic flux. The magnetomotive force, abbreviated as mmf, is comparable to the electromotive force and may be thought of as the flux-setting factor. The mmf is measured in ampere-turns and is comparable to the number of turns of wire carrying an electric current.The mmf rises as the current through a coil (as in an electromagnet) or the number of turns of wire in the coil is increased, and the magnetic flux increases accordingly if the remainder of the magnetic circuit stays unchanged. A magnetic circuit’s reluctance is similar to an electric circuit’s resistance. Reluctance is determined by the geometric and material aspects of the circuit that provide resistance to the presence of magnetic flux.

A given component of a magnetic circuit’s reluctance is related to its length and inversely proportional to its cross-sectional area and permeability, a magnetic property of the supplied material. Iron, for example, has a very high permeability in comparison to air, therefore it has a very low reluctance, or gives very little resistance to the presence of magnetic flux. In a series magnetic circuit, the total reluctance is the sum of the individual reluctances encountered around the closed flux channel.

Magnetomotive Force Definition

The presence of electromotive force causes current to flow in an electric circuit, while the presence of magnetomotive force (MMF) causes magnetic flux to flow in a magnetic circuit. Magnetomotive Force is the magnetic pressure that creates the magnetic flux in a magnetic circuit. The SI unit of magnetomotive force is ampere – turn (AT) and in CGS system is G (gilbert). The MMF for the inductive coil seen in the diagram below is,

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The product of the current around the turns and the number of turns in the coil equals the MMF’s strength. Under work law, MMF is defined as the force required to move the unit’s magnetic pole once around the magnetic circuit. Therefore, the magnetomotive force formula is expressed as,

F_m = NI

Here, F_m is the magnetomotive force, N is the number of turns and I is the current flowing through a coil.

The magnetic potential is another name for the MMF. It is the property of a substance that causes a magnetic field to form. The product of magnetic flux and magnetic reluctance is used to compute the magnetomotive force. The resistance is the magnetic field’s opposition to establishing the magnetic flux on it. The reluctance and magnetic flux MMF is given as,

F_m =
ФR

Here, Ф is the magnetic flux and R is the reluctance of a circuit.

The magnetomotive force may be measured in terms of magnetic field intensity and material length. The magnetic field strength is the force acting on the magnetic field’s unit pole. The MMF for field intensity is stated as,

F_m=Hl

Here, H is the magnetic field intensity and l is the material length.

Two measures are there, such as distance and displacement, appear as the same, but both are dissimilar with altered meanings and explanations. The distance can be explained as the measurement of total space that an object has completed at a time during its motion.

• Distance is reserved as a scalar quantity that depicts “how much space an object has traveled” in the course of its motion. 

• Displacement is reserved as a vector quantity that mentions “the course of an object from its original to its final position”; it is the object’s complete alteration in position.

Further, the displacement can be signified as the measurement of total space covered by an object along with its significant direction. We have concluded the vital modification between distance and displacement.

The distance is a mathematical measurement of how distant apart substances or places are. In our daily usage, distance can be referred to as a physical length or approximation built on other criteria (e.g., distance over two cities).

What is Distance in Physics?

Distance is the summation of the movement of a body without considering its direction. We can express distance as the total space, which is covered by an object despite its first or last point.

• Distance and displacement are dissimilar measures, but they are interconnected. The distance should be equal to the displacement’s magnitude.

• Distance and displacement have the identical size only when we deliberate small intermissions. Meanwhile, the displacement is calculated along the straight (shortest) path between two points, and its value is always equal or lesser than the distance.

Several things can be meant about physical distance, such as:

• Distance Traveled: The specific path’s length is covered between two junctions, for example, the distance covered by walk while directing a maze.

• Straight-Line Distance or Euclidean Distance: The length of the path in-between two points is the possible shortest path through space that could be considered if there were not any hurdles.

• Geodesic distance: The length that falls between two points as the shortest path while enduring on some surface, for example, the distance of the great-circle along the curve of the Earth, the length of a precise path that comes back to the initial point. 

• For example, a ball is thrown straight upward direction or the Earth when it completes one orbit.

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Let’s visualize this diagram. Can you calculate the overall distance?

From the figure, the total distance covered by the boy will be:

D = (4 + 3 + 5) meter = 12 meters.

What is the Distance Between two Points?

Distance between any two points can be measured through the length. For instance, it has been concluded that the distance of a road is alternatively spoken how long the road is?

In the metric measurement system, the most shared units of distance are kilometers, meters, centimeters, and millimeters.

The alteration in this place can be calculated through the measurements of distance.

This permits us to distinguish how slowly, or fast motion is. There is a motion everywhere, such as the motion of a snail on the ground, a butterfly flying from flower to flower, and the flowing of the river in the obstacle-free paths. 

Besides, the flying of an airplane is high enough in the air, which makes jet trails, the moon rotating around the Earth, blood traveling inside our bodies, and many more.

The total distance covered = speed * total time taken.

Metric Units of Length Conversion Chart

Here you will find the unit of length conversion customary to metric units of lengths.

When the length is used in mathematics, we have an idea that ‘Meter’ is the standard unit of length, which is inscribed in short denoted by (m).

A metre length is separated into hundreds of equal parts, where a single part is centimetre symbolized as cm.

As such, 100 centimetre is 1 metre and 1 metre is 100 centimetre.

We know its use, such as kilometer is utilized for measurements of the long distances. We know that 1 kilometer equals 1000 meters. Here, the kilometer is written in short as km.

Metric Length Conversions

Measurement of Length Distance

The distance can be exemplified as follows:

d = s * t

Where,

d = the distance traveled in metre

t = time taken to cover the distance in second

s = the speed in metre/sec

Generally, we use Kilometer as km, Meter as m, & Centimeter as cm as the length measurement units in our daily usage. These are the most used parameters for the measurement of distance.

The term micrometre, as used by the International Bureau is used in Weights and Measures. The SI symbol μm is also commonly called as a micron that is an SI derived unit of length equalling 1×10−6 which is the metre that is the SI standard prefix “micro-” = 10−6. Micrometer is the one-millionth of a metre that is or one-thousandth of a millimetre which is  0.001 mm or about 0.000039 inch.

What is a Micrometer

The width that is of a human which is single hair ranges from approximately 20 to 200 μm. The longest human chromosome that we are talking about is said to be approximately 10 μm in length. We can say that this is around 100 μm that is 0.1 millimetres which is the smallest thing visible to the naked eye.

The term which is micron is also the symbol denoted by μ were officially said to be accepted for use in isolation to denote the micrometre in 1879 but was officially revoked by the International System of Units that is the SI in 1967. This generally became necessary because of the reason that the older usage was incompatible with the official adoption which was of the unit prefix micro- which is denoted by μ during the creation of the SI in 1960.

In the SI unit, the systematic name which is micrometre that has become the official name of the unit and μm became the official unit symbol.

‘Micrometer’ Symbol 

Additionally, we can say that in American English the use “micron” generally helps differentiate the unit from the micrometer which is a measuring device. In 1950 the plural of micron was officially called “microns”, though “micra” was occasionally used before.

The official symbol which is generally used for the SI prefix micro is the Greek lowercase mu. In the Unicode, we can say that there is also a micro sign with which the code point that is U+00B5 (µ) is said to be distinct from the code point U+03BC (μ), which again we can say is of the Greek letter lowercase mu. And again if we see according to the Unicode Consortium that is the Greek letter which is swift or character is preferred but during implementations, we must recognize the micro sign as well. Most of the fonts which we know use the same glyph for the two characters.

Principle of Micrometer Gauge

A micrometer sometimes is also known as a micrometer screw gauge. It is a device which is said to be incorporating a calibrated screw that is widely used for accurate measurement which is of components in mechanical engineering and machining as well as most mechanical trades also. That is we can say which is along with other meteorological instruments that are such as dial and then the vernier and digital callipers. The micrometers which are said to be usually but not always in the form of callipers that are opposing ends joined by a frame. 

Micrometers are also used in telescopes or we can say in the microscopes which is to measure the apparent diameter that is of celestial bodies or the objects that are microscopic objects. 

Micrometers which we know already use the screw to transform small distances that are too small to measure directly which are into large rotations of the screw that are big enough to read from a scale. The basic operating which is said to be the principles of a micrometer are as follows:

1. The constant is called the screw’s lead. The head of the screw’s lead is the distance it moves that is said to be forward axially with one complete turn that is to 360.  We can say that in most threads and all single-start threads, generally lead and pitch refer to essentially the same concept.

2. Here we can say that with an appropriate lead and major diameter of the screw. a given amount of axial movement will be amplified in the resulting circumferential movement.

For example, we can say that if the lead of a screw is 1 mm but the major diameter which is the outer diameter is 10 mm, we can say that then the circumference which is of the screw is 10π or about approx which is 31.4 mm. Therefore we can say that an axial movement of 1 mm is amplified that is magnified to a circumferential movement of 31.4 mm. 

The monoclinic system is the structural category of crystalline solids. Well, crystalline solids can be categorized according to the structure of crystals. In the monoclinic system, crystals are referred to mainly three axes, a, b, and c, where axes a is perpendicular to axes b and c, but simultaneously, a and b are not perpendicular to each other. Suppose atom groups or atoms in crystalline solids are represented by points and lattices when points are connected with each other. The monoclinic unit cell is differentiated by a single axis called two-fold symmetry, where the monoclinic unit cell can be rotated by 180 degrees without disturbing appearance. Some of the solids that belong to the monoclinic crystal system are borax, gypsum, beta-sulfur, orthoclase, muscovite, kaolin, clinoamphibole, azurite, jadeite, and spodumene.

What is Crystallography and its Types?

Crystallography is the study of the arrangement of bonds of atoms in crystalline solids. In this system, mainly atoms arrangement is studied based on the crystal lattice. In modern days, DNAs and minerals are examined through crystallography. Well, many kinds of crystal systems are used nowadays. All the structure is defined based on three factors: how many axes used, length, and angles of the axis. 

Six different crystal systems are isometric system, tetragonal system, orthorhombic system, monoclinic system, triclinic system, hexagonal system, trigonal subsystem. All these systems have three axes, and the direction of the axis indicates the sides. The longest axis is C, and the shortest axis is A, and axis B is also there; in some systems, you can see axis D.

Monoclinic Crystal Shape And Monoclinic Crystal Angles

In crystallography, the monoclinic crystal system is one of the practical crystal systems. Three vectors describe a crystal system. In the monoclinic system, the quartz is described by vectors of inequitable lengths, as in the orthorhombic system forming a rectangular type prism with a parallelogram base. Hence two combinations of vectors are perpendicular (join at right angles), while the third pair forms an angle other than 90°.

• Orientation of a crystal has few constraints – where b is the only fixed axis by symmetry.

• Axis C is generally chosen based on cleavage and habit.

• α and γ = 90

• In some cases, the b axis will be 90 degrees that result in pseudo- orthorhombic form.

• Symmetry operation in a monoclinic system, the unprecedented operation is 2/m – a twofold axis of rotation with a mirror plane.

• The axis b is the rotation, while c and a lie in the mirror plane

• Monoclinic crystals have two forms: pinacoids and Monoclinic shape crystals have two shapes: pinacoidal and prisms.

• Common monoclinic rock-forming crystals include clinopyroxene, orthoclase, mica, and titanite.

Orthorhombic System In Crystallography

As we have discussed, crystallography has many types, and the orthorhombic system is one of them. Orthorhombic lattices are formed by extending cubic lattices with two orthogonal pairs by two different factors. While raising the cubic lattice with the two factors, a rectangular prism is formed, and axis a and b form the rectangular prism base. Axis c determines the height of the prism in the orthorhombic system in crystallography. Here all three-axis a, b, and c are different and intersect each other at the rectangle. Hence, all the three orthorhombic lattice vectors remain mutually orthogonal.

• In Orthorhombic crystallography, all the three-axis are of a distinct length that is mutually perpendicular to each other.

• Convention has it that a crystal is oriented so that c is the most significant axis and a minor axis.

• In such a case, b is taken as unity, and after that, you can calculate ratios.

• The unique symmetry operation in an orthorhombic system is The special symmetry operation in an orthorhombic system is 2/m 2/m 2/m – Three twofold axes of rotation coinciding with the three crystallographic axes.

• There are three types of patterns in the class: prisms, pinacoids, and dipyramids.

• Common orthorhombic rock-forming minerals incorporate andalusite and sillimanite, olivine, orthopyroxene, and topaz.

Forms of Orthorhombic System in Crystallography

The orthorhombic system has two types of forms, unique form, and general form. A possible form has the maximum number of faces of any pattern in its crystal class. Particular forms may appear in any crystal class of the system. In general form, three-axis a, b, and c intersect with each other at a specific angle, and it will never be zero. Different forms are pyramid, prisms, domes, disphenoid, sphenoid, pedion, pinacoids, and dipyramid.

The eyes are the sense organs of sight in our body. Each eye is a spherical-ball like structure and is referred to as the eyeball. The ability of the eye to see the object equally clear from various distances is called the power of accommodation. However, this power of accommodation can get defective at times. Like some times the eye is not able to see distant objects for eg. Highway signs clearly while sometimes it is not able to see near objects clearly. Here we are going to learn about the defect of the eye where distant vision is blurred while near vision is clear. Such a condition or abnormality of the eye is known as myopia. Let’s study this defect of the eye (myopia)in detail.

 

What Is Myopia?

Myopia is an eye defect or common abnormality of the eye in which the near vision is clear while distant vision is blurred. This condition is known as myopia also it is called near or short-sightedness.

 

Retina is that part of the eye which provides a surface for image formation. In myopia what happens is light rays entering the eyes converge too soon and are brought to focus before reaching the retina hence the image cannot be formed on the retina.

 

Causes Of  Myopia

This eye defect called myopia can be caused basically due to the defected eye structure.

 

Structure of the eye causing myopia can have two defects:. 

• The eye lens becomes too convex or curved 

• Depth of the eyeball is too much i.e. eyeball lengthened from front to back. When the length of the eyeball is too long as compared to the focusing power of the lens of the eye and cornea. Because of this, the light rays focus at a point in front of the retina and not on the retina itself.

Because of the above mentioned defects in the eye structure, the light that enters our eye doesn’t focus correctly. Hence, images are formed in front of the retina which is the light-sensitive part of our eye instead of being formed directly on the retina which causes blurred vision.

 

Myopia is also referred to as the refractive error.

 

In the above diagram, we can see that due to the eye lens being too convex or curved the image formation that should happen on the retina is happening in front of the retina. Thus, causing blurred vision of distant objects known as myopia.

 

Types of myopia:

• Simple Myopia – In this, the eye of a person is almost healthy, wearing glasses or contact lenses of suitable power can easily correct the defect and can correct the issue of a person’s eye vision.

• High Myopia – High myopia is a severe form of myopia. When a person is diagnosed with myopia at a young age then with the growing age this defect becomes worse. High myopia increases the chances of development of other eye problems such as cataract, glaucoma etc.

 

Myopia Correction

Myopia isn’t a very complex disability. It can be corrected easily by wearing concave lenses. Concave lenses cause parallel rays of light to diverge before they converge and focus on the retina. 

 

Let’s understand it more easily through a diagram:

 

Whenever asked what lens is used in myopia or what lens is used to correct myopia the answer should be the concave lens.

 

Now we will talk about the symptoms and also the treatment of this eye defect known as myopia.

 

Myopia Symptoms And Treatment

Symptoms of Myopia:

• If a person is myopic he or she will not be able to see the road signs and distant objects clearly but the nearer object will be visible to him/her clearly.

• Feeling of fatigue while playing sports or driving is also a symptom of myopia.

• When there is a need to close eyelids partially to see clearly or there is a need to squint is also a symptom of myopia.

• Eyestrain is caused due to myopia

• Headache is another symptom of myopia

• squinting and frowning.

• complications as a result of eyestrain.

 

Treatment of Myopia 

After a person is diagnosed with myopia he can have the following ways to treat this eye defect.

The custom lenses fit into frames and are worn as specs while the contact lenses are discs that sit on the surface of eyes.

 

• Orthokeratology – Orthokeratology is using overnight rigid contact lenses to reshape the cornea. It really works with the aid of pulling down the significant cornea, thinning the central corneal epithelium, thickening the mid-peripheral cornea, and producing a myopic shift in peripheral vision. This quickly reduces or eliminates refractive errors and decreases the want to put on contact lenses or spectacles in the daylight hours. Researchers observed that orthokeratology is as effective as atropine in delaying myopic progression.

Orthokeratology is a nonsurgical method for the treatment of myopia. This can be helpful in the treatment of a mild form of myopia. This treatment involves wearing a series of rigid contact lenses to reshape the cornea.