Category: Physics Notes PPT

A.C. motors are induction motors. The air A.C. motor is a motor that transforms alternating current into mechanical energy. 

Working Principles, Construction, Classification, and Types

Working Principles

Induction motors operate on the theory that when a closed conductor is placed in a magnetic field, it produces torque, or on the combined action of electromagnetic induction and the motor principle.

Construction

The three-phase induction motor is made up of two parts:

Stator

It is built out of a steel frame that surrounds a hollow, cylindrical cone made up of thin silicon steel laminations to minimize eddy current and hysteresis loss. On the inner periphery of the core, a huge number of similar slots are carved.

The stator conductors are inserted into these slots, which are isolated both from one another and from the slots themselves. A balanced star or delta winding is used to link the conductors. Depending on the speed requirement, the windings are wound for a specific number of poles.

When high speed is required, the winding is wound with fewer poles and vice versa.

Rotor

Any mechanical load can be linked to the rotor, which is positioned on the motor’s shaft. There are 2 types of rotors:

A squirrel-cage rotor’s core is a cylindrical laminated core. It also has parallel slots for rotor conductors. Heavy copper or aluminum bars serve as the rotor’s conductors. Each slot receives one bar.

The rotor is made of laminated materials. The cylindrical core features uniform slots in which three-phase star-connected winding is installed. The open ends of the star winding are connected to three insulated slip rings installed on the motor shaft, which are coupled to carbon brushes.

Types

The different types of AC motors are:

A Brief Description of A Switch

As we all use switches to control various electronic devices in our day-to-day life, this article deals with switches and their types. It aims to give a basic idea about switches and their types. Switches are important but they are not given the respect that they should be getting since their availability. 

Meaning of a Switch

What do you understand from the terminology Switch? A switch is an electrical device that is used to interrupt the flow of electricity or in simple terms turn on or turn off any electronic appliance like – fans, lights, television, computer, washing machine, etc. A switch is used to make or break the electronic circuit when the switch is on it means the circuit is closed and the current is flowing and when it is off, the circuit is open and there’s no flow of current.

Mechanical Switches.

Depending upon poles and throws mechanical switches can be classified into various types. These can be explained as follows along with sub-categories: 

1. Single Pole Double Throw

 Single pole double throw switch which has two terminals; one input terminal which is referred to as pole and one output terminal known as throw. Hence it got the name single pole single throw. This switch is one of the simplest examples of switches. This switch is generally used in a single loop, which means the circuit requires to control only one close path.

2. Single Pole Double Throw

It has three terminals, two output terminals, and one input terminal. We can also use this switch to supply current to two loops. It is also known as a selector switch.

3. Double Pole Single Throw

These   Double pole single throw switches are used to control the two circuits at the same time. It consists of four terminals, two input terminals, and two output terminals. These types of circuits have two switches and are connected with a single lever so that they can operate at the same time. It can be said that DPST switches are very similar to two SPST.

4. Double Pole Double Throw

This switch has six terminals, two input terminals (poles), and four output terminals (throw), two for a terminal for each pole. In a double pole double throw switch, one pair of output or throw is connected with two terminals of input or pole.

5. Two Pole Six Throw

It is made up of 12 output terminals- six output terminals (throw) for each pole and one input terminal (pole). This type of switch is generally used for change-over in the circuit with a common input terminal.

6. Momentary Control Switches

These are further divided into various categories. Few of them are as follows: 

Temperature switch: Various temperature sensing devices like RTD (resistance temperature device) are composed in this type of switches. This switch operates according to the value of measured temperature.

Toggle Switch: This type of switch is very common and used in household applications to ON and OFF electrical appliances. It has a lever by which we can move up or down to ON and OFF appliances. 

Rotary Switch: This type of switch is used for connecting one line with another of the many lines. Nob of multimeter, channel selector, range selector metering device band selector in communication devices is the example of this type of switch. This switch is similar to a single pole multi throw switch. But the arrangement of this switch is different. 

Electrical Switches

Power Diode

To construct power diodes silicon is used. When the pn junction is reverse biased the power diode acts as switch off and it acts as switch on when the pn junction is forward biased.

Bipolar Transistors

A transistor works similar to that of a normal switch.  Transistor’s active region is not used for switching applications. When the transistor works in the saturation region, it is on and it is off when it works in the cut-off region. For npn and pnp transistors, to operate it as a switch when it’s on a base current needs to be supplied.

MOSFET

MOSFET- Metal Oxide Semiconductor Field Effect Transistor which is a unipolar switching device. It is made up of three terminals: drain (output), source (common), and gate (input). As the device is voltage controlled, the on and off state of the device can be determined by controlling the input voltage and resistance across the drain and the source. 

Pressure in physics is the amount of force applied normal to the surface area of an object. In other words, it is the force applied per unit area. Therefore, it is different from the total force that operates on a surface. It is also possible to apply and maintain single point stress on a solid.

 

Nevertheless, the surface of a sealed substance, i.e. a fluid or gas, can only be overcome by pressure. Therefore, in terms of pressure, it is more useful to describe the forces that operate on and within the fluids. 

 

Units of pressure are often expressed as P = FA

e.g. pounds per square inch (psi), dynes per square inch, or Newtons (N) per square meter (Nm²)

 

Definition of Pressure:

The pressure is defined as the force per unit area which is perpendicular to the surface. Thus, the formula is often expressed as P = FA

 

Pressure is designated with the letter although the capital letter “P” can also be seen being used on some occasions.

 

What Does this Force Per Unit Area mean?

The force per area implies that a given region is impacted by a certain power. When we look at force, it is expressed as. Since there are so many different engineering systems used for both mass and area, there is a huge number of these variations. In fact, there are also many stress units that do not have the mass or region in their names explicitly, although they are sometimes identified.

 

It is good to notice that in practice the “force” is not always included in the pressure unit names. 

 

For Example:

Pressure should be indicated as kilogram-force per square centimetre as kgfcm², but often it is expressed as without the force “f”.

 

Similarly, pound-force per square inch (pfsi) is generally expressed as pounds per square inch (psi).

 

What is the SI Unit of Pressure?

SI method is the most frequently employed measurement system in the world. It was published in 1960, but before that, it has a very long history.

 

SI Unit of Pressure:

For pressure, the SI system’s basic unit is Pascal (Pa), which is Nm² 

 

In formula, we can express it as:

 

Pa = Nm² = kgm xs²

Pascal is a low-pressure unit. The usual atmospheric air pressure is equivalent to approximately 101325 Pa.

 

Using Pascal’s definition, the can be substituted with different units such as g(gram), force, and metre can be replaced with centimetre or millimetre. 

 

By doing this, we get other variations or units of pressure, including kgfm², gfm², kgfcm², gfcm²,  kgfmm², gfmm² just to list a few of the units.

 

The unit “bar” in some regions is still used often. It is based on the metric system but does not adhere to the SI system. Bar being 100000  times Pascal (i.e. 100 times kpa), it is anyhow easy for conversion. 

 

A uniform prefix scheme has been set up since the calculated amounts can have such a wide range.

 

And as with all pressure units, whether SI or not, we can use the standard prefixes/coefficients before them such as milli 1100, centi 110, hector , kilo (1000) , and mega (1000000).

 

Just to mention a few instances, we already have different units, all of which are widely used: Pa, hPa, Mpa. The unit bar is most commonly written without using a prefix or with using a prefix for ‘milli’ as bar.

 

But we get a number of variations by having all the volume units and integrating them with all the SI framework zone units.

 

Although the SI design is used in several countries, many other pressure models are still being used as well. So, let us look at other such systems.

 

Imperial Units

For nations using the Imperial system (such as the United States and the United Kingdom), the construction units used for both volume and area vary from the SI standard system.

 

Mass is generally measured in pounds or ounces and the area and length with feet or inches.

 

Thus, some of the pressure units derived are lbfft², psi ,ozfin², iwc , in H₂O , ft FH₂O.

In the United States (U.S.), the common pressure unit used generally is “psi” (i.e. pounds per square inch). And for all the process industries, a common unit for pressure used generally is also in H₂O (inches of water).

 

Liquid Column Units

By using fluid in a translucent U-tube, the older pressure monitoring tools were often made. If the force is the same at both the ends of the pipe, the amount of water on both sides is the same. But if the forces vary, there is an inequality in the amounts of water.

 

The variation in the rate is linearly proportional to the difference in pressure. For example, you could keep one side of the pipe exposed to the ambient pressure of the space and attach the force to be tested to the other side.

 

What is the CGS Unit of Pressure?

The abbreviation “CGS” is based on “centimetre-gram-second” terms.

 

As these terms indicate, the CGS system is a variant of the metric system, but instead of using the metre, it uses centimetres as the measure of distance and grams as the unit of weight instead of kilograms.

 

Using these common CGS based units; various different CGS units used for depictions in mechanical systems have been built.

 

The CGS is a pretty old method and was preceded mostly by the MKS (metre-kilogram-second) process, which was substituted by the SI system. Nevertheless, sometimes you can also run into pressure CGS programs.

 

The CGS base pressure unit is barye (Ba), which equals 1dyne per square centimetre.

The “dyne” is the needed force for the acceleration of one gram’s mass to a rate of one centimetre per second.

 

The pressure unit conversion can be expressed as,

 

1 Ba = 0.1 Pa

 

Other Units of Pressure

The other units of pressure can be expressed in the standard unit of “bar” can be expressed as:

1. 1 torr = 1.3332 x 10⁻³ bar

2. 1 at = 0.980665 bar

3. 1 atm = 1.01325 bar

Thus, many different types of units and prefixes may be used in general practice to reflect pressure. Thus, it is very important to ensure that all the measurements and their respective units are in the same framework when conducting pressure calculations.

 

In physics, pressure is referred to the quantity of force that is applied normal to the surface area of the object. It can also be termed as the force which is applied for each unit area. This is why it is different from the total force which operates on the surface. It is possible to apply as well as maintain the single point stress on the solid.

The surface of the sealed substance which is fluid
or gas, can be overcome only by pressure. This is why, when talking about pressure, it is useful to explain the forces which operate within the fluids. The units of pressure are generally expressed as  P = FA. The examples include dynes per square inch, pounds per square inch, and Newtons per square metre. 

Definition of Pressure

The pressure can be defined as force per unit area that is perpendicular to the surface. The formula for this can be expressed like P = FA. The pressure can be designated with the letter even though the capital letter “P” is also used on some occasions. 

Understanding Force Per Unit Area

The force per unit area means the given region is affected by a certain power. Since there are various engineering systems that are used for both area and mass, there can be a large number of variations. There are various stress units that don’t have region or mass explicitly in their names even though they can be sometimes identified. 

Example:

The pressure must be indicated as the kg-force per square cm: [frac{kgf}{cm^{2}}] but is often denoted without force ‘f’.

The SI unit of pressure: The SI unit is one of the most frequently used measurement systems around the globe. The basic unit for pressure in the SI system is Pascal (Pa), which is[frac{N}{m^{2}}] .

In the formula,this can be expressed as [pa=frac{N}{m^{2}}=frac{kg}{mXs^{2}}]

Pascal is the unit of low pressure. The usual air pressure of the atmosphere is approximately equal to 101325 Pa.

Using the definition of Pascal, it can be substituted with different units, like gram. Similarly metre and force can be replaced with millimetre or centimetre. 

Imperial Units

For those countries that use the imperial system, like the US and the UK, the construction units for both area and volume vary from the SI standard system. The mass is usually measured in ounces or pounds, and the length and area with inches and feet. Some pressure units that are derived are[frac{ibf}{ft^{2}},psi,frac{ozf}{in^{2}},in H_{2}o,iwc, ft FH_{2}o].

In the US, the common unit that is used for pressure is generally psi, which is pounds per square inch. And for the majority of the processing industries, the common unit that is used for pressure is in H₂O (inches in water). 

CGS Unit of Pressure

The CGS system is considered as the variant of the metric system, however, it uses centimetres instead of using a metre, as the measurement for distance and it uses grams for the unit of weight in place of kilograms. 

The CGS is an old method and it has been preceded by the MKS process, and which was then substituted by the SI system. The CGS base unit for pressure is barye (Ba), which is equal to 1 dyne per square centimetre. Dyne is the force needed for acceleration of gram’s mass to the rate of 1 cm/second. 

The unit conversion for pressure can be expressed as

1Ba = 0.1 Pa.

Students should learn about mass, as it is very important before understanding the unit of mass. In simple words, mass is the quantity of matter in an object. It can be considered as both a property of a physical body as well as a measurement of its resistance to acceleration when some quantity of force is applied. However, the important point a student should remember is that mass is different from the weight even though the term might sometimes be used interchangeably, as they have different units.

The matter which is present in a given object is known as mass, and the most commonly used units of measurement are:

Mass can also be termed as the number of atoms and molecules present.  In science, mass is measured in metric system units using kilogram (a thousand grams), grams, centigrams (hundredth of grams), and milligrams (thousandth of grams).

Unit of Mass

a. SI Unit of Mass

The standard unit of mass is Kilogram (kg)

In SI units, following units are accepted: gram (g) and its multiples and submultiples, a tonne (t) or metric ton, electronvolt (eV), the atomic mass unit (u) which is most convenient for denoting the masses of atoms and molecules.

b. Cgs Unit of Mass

Centimeter gram second, otherwise the CGS system of units is a metric type system based on centimeter as unit of length, gram as unit of mass, and second as unit of time.

Some Common Units of Mass

 

Metric Units of Mass

To measure the weight of an object, mass is used. For example, when you step on a scale, you measure the mass of your body.

The most common units to measure mass in the metric system are gram and kilogram.

How much is a Gram?

The mass of a small paperclip is about 111 grams.

How much is a Kilogram?

The mass of a wooden baseball bat is about 111 kilogram.

Measurement of Mass

The amount of matter within an object is represented by mass, but measuring mass doesn’t necessarily mean that you have measured weight since weight changes due to gravity’s effect. However, mass does not change regardless of where the object is located, the amount of matter remains the same. Depending on the size and location of objects, scientists use various tools to measure mass.

Mass is measured by a beam balance device, also known as mass scales, balance scale, simply scales, mass balance, weight scales, or weight balance.

As mentioned above, a number of tools exist for measuring mass in different environments like balances and scales, measurement transducers, Newtonian mass measurement devices, vibrating tube sensors, and use of gravitational interaction between objects.

a. Balances and Scales

For daily use objects, scientists use a balance to obtain the object’s mass. One of the examples of balance is triple beam balance. There are different types of balance, which include beam balances and digital scientific balances. In space, scientists use the inertial balance to measure mass.

b. Measurement Transducer

Sometimes mass cannot be determined by using a balance. Transducers are used by scientists to measure the mass of a liquid in a calibrated tank. It also measures the mass when the properties of the liquid are in a static state. A signal is sent to the processor through a transducer, which makes the mass calculations displayed by an indicator. Taking measured mass of liquid below the transducer, and subtracting the mass of vapor, the mass of a floating roof, the mass of bottom sediment and water yields gross mass.

c. Space Linear Acceleration Mass Measurement Device (SLAMMED)

SLAMMED is one of the most sophisticated mass measuring devices used to measure the mass of humans in orbit, currently stationed on the International space station. SLAMMED is a piece of rack-mounted equipment that is based on Sir Isaac Newton’s law of motion, where force equals the product of mass and acceleration. By using two springs that exert force against a person, this device determines the person’s mass via force and acceleration.

Evolution of SI and CGS Unit

In the mid-nineteenth century, scientists had a discussion on how to extend the metric system of physical units such as force, pressure, work, and power. In order to carry out this, there should be a coherent way, a clear choice should be made on what metric units the distance, mass, and time should be provided. A group of scientists along with the Scottish mathematical physicist James Clerk Maxwell and the Scots-Irish physicist William Thomson (later ennobled as Baron Kelvin) was successful in the argument to select the centimeter, gram, and second, and therefore the CGS System was formed.

In 1874, the CGS system was formally accepted and introduced by the British Association for the Advancement of Science. It favors the working scientists, and it has been commonly followed in scientific work for many years. Engineers preferred a system based on larger units due to the reason that the CGS units are relatively small in size. Within a few years, the MKS system which is based on the meter, kilogram, and second, emerged as a competing choice for a coherent system of units.

In the 20th century, commercial transactions, engineering, and other practical areas used metric units or MKS units more. In 1950 there was some discomfort in using the metric units in translating between CGS and MKS units that went against the metric ideal of a universal measuring system.

Adaptation of the meter, kilogram, second, ampere, degree Kelvin, and candela as the basic units for all international weights and measures was done in 1954 at the Tenth General Conference on Weights and Measures (CGPM). The International System of Units (SI) for the collection of units was adapted at the Eleventh General Conference in 1960. These decisions gave the central core of the MKS system over the CGS system. The CGS units are still in use for various purposes, they are gradually being replaced by the SI units.

Differentiation between MKS and CGS Unit

MKS Unit

• The unit system in which fundamental or basic quantities such as length, mass, and time are measured in terms of meter, kilogram, and second.

• MKS is the abbreviation of Meter, Kilogram, and S
  econd.

• They are large scale units used to measure long distances and larger objects

• MKS consist of Meter, Kilogram, Second, Newton, Joule, Watt, etc.

• It is also called SI unit system or System International system.

CGS Unit

• The unit system in which the fundamental or base quantities such as length, mass, and time are measured in terms of the centimeter, gram, and second.

• CGS is the abbreviation of the Centimeter, Gram, and Second.

• They are small-scale units used to measure small distances and small objects.

• CGS consists of the gram, second, dyne, erg, etc.

By definition, the wavelength is the distance between two consecutive crests and troughs. In simple words, the distance between two subsequent peaks in a wave is known as wavelength. To better understand the concept of wavelength, let’s take a deep dive into what waves are. 

What are Waves? 

Waves are disturbances that travel from one location to another in a medium. When waves are propagating from one point to another, the medium remains stationary for the larger part and moves locally.

A perfect example of a wave would be a telephone coil. When you take a telephone coil and stretch it slightly, you’d get a squiggly shape with even spaces between each upward and downward curve. Holding the coil at this position would be known as the rest position or equilibrium. Now if you move the coil from one end in any direction, the entire coil would go through a disturbance before coming back to the rest position. 

The act of creating a disturbance in the coil before it comes back to the rest position would be known as ‘pulse’. However, if you make the same disturbance repeatedly, it would result in the coil moving continuously and periodically in a back and forth manner. The repeated and periodic disturbance that moves through a medium for a prolonged period of time from one location to another is known as a wave. 

What is a Medium? 

We talked about the concept of a medium in the previous paragraph but what does it actually mean? A medium is a substance or material which carries a wave. The medium doesn’t make or produce a wave, but simply transports or carries it from one point to another. For example, in the telephone coil, the wave was not produced by the coil itself, however, it was able to travel from one end to another due to the particles in the coil. The particle to particle interaction in a medium is what results in the propagation of the waves. 

To understand the nature of a wave, it is important to consider the medium as a collection of interacting particles. To visualize this concept, imagine a house of cards, now the cards are the medium. If you push even one of the cards in the house, the ones adjacent to it will also feel the force applied and therefore move away. This disturbance would result in a wave, where every particle (card) would interact with one another to carry the wave to the entirety of the medium (house of cards).

About Waves, Transmit Energy

One of the unique properties of waves lies in the fact that waves transmit energy without transporting matter. When a disturbance is caused in the medium, the waves carry over the energy from one particle to another without transporting or disturbing the matter at all. For eg; when someone pushes a ball down a hill, the energy is transported from the top of the hill to the ground, however, this action is possible only when the ball rolls down the hill too. However, in a wave, for eg, in a telephone coil, the energy is displaced from one particle to the coil to the other till it reaches the end of the coil, but the matter (or particles of the coil) remain stationary as once the energy has been displaced from one crest to the other, the previous particle reverts back to its rest position (state of equilibrium). 

How was the Wavelength Discovered?

The waves were discovered in the 1800s by Sir William Herschel when he was exploring the question of how much heat was contained by the different colors of visible light. He conducted an experiment, where he used a glass prism to break down white light into its composing colors. After this, he placed a thermometer under each color and placed another thermometer just beyond the range of red light, which is the last color in the VIBGYOR spectrum. Through this experiment, he discovered that the thermometer that was placed beyond the range of white light has the highest temperature. And this was the story of how infrared waves were discovered. Based on this discovery, many scientists went forward and discovered many other components and types of waves. 

Components of a Wave

A wave consists of the following components: 

• Rest position: the undisturbed position of the particle is known as the rest position. In a diagram or graph, the x-axis of the graph is known as the rest position. 

• Displacement: the entire length of the wave from one end to another is known as displacement. 

• Crest: the highest point of the peak from the rest position is called a crest. 

• Trough: the lowest point of the peak from the rest position is called a through.

• Amplitude: the distance between the crest or trough from the rest position is known as amplitude. 

• Wavelength: the distance between two consecutive crests or troughs is called a wavelength. It is denoted by the Greek symbol lambda ƛ. The standard unit of wavelength is metered (m). 

• Time period: The time taken for a wave to complete one whole cycle of a crest and trough is known as the time period. The SI unit of the time period in seconds (s). 

• Frequency: the number of waves that pass through a point per second derives from the frequency of the wave. Frequency is measured in Hertz (Hz). 

How is Wavelength Calculated?

The wavelength of a wave is calculated by dividing the velocity of a wave by its frequency. 

wavelength= wave velocity/ frequency

ƛ = v/f

Here, ƛ = distance between the two consecutive crests or troughs in meters. 

           V = velocity of the speed of waves moving in a direction, calculated in m/s.

           f = frequency of the wave in Hz or per second. 

Types of Waves

Waves come in many shapes and forms and usually have the same characteristics to a certain degree. However, based on some distinguishing factors, we can categorize waves into two different categories. 

Basis of the Direction of Movement

Categorizing waves on movements results in three different categories: 

• Transverse Waves: transverse waves are the waves in which the particles of the medium move perpendicular to the direction in which the wave moves. For eg, in a telephone coil, when the disturbance is induced at one end, the wave moves from left to right. However, the particles of the coil oscillate in up and down motion. This results in a formation of a transverse wave. 

• Longitudinal Wave: Longitudinal waves are the waves in which the particles of the medium move parallel to the direction of the wave. A sound wave is a classic example of this type of wave. When a sound wave is produced, the sound wave moves from the lips of the speaker to the ears of the listener. While the air molecules that carry the sound wave vibrate back and forth in the same direction of the wave. When one strikes a tuning fork against a hard surface, the pitches of the tuning fork move back and forth rather than up and down. 

• Surface Wave: A surface wave is a wave in which the particles of the medium undergo a circular motion. These types of waves are considered either transverse or longitudinal. For example, the waves on the surface of the ocean do not move back or forth or up and down, instead, they fold over and move in a circular motion. 

Basis of Medium 

This categorization rests on the principle that a wave can transmit energy in a vacuum or not. This type of categorization leads to two types of waves: 

• Electromagnetic Waves: an electromagnetic wave is a wave that is capable of transporting energy through a vacuum. These waves are produced from the energy of charged particles. The sun rays are the best example of this type of wave since sun rays can easily transmit energy even without a medium. 

• Mechanical Waves: waves that require a medium to transport energy and are incapable of existing in a vacuum. A sound wave is an example of a mechanical wave since sound waves can only be produced through the oscillation of air molecules. This is the reason why one can’t hear anything in space. 

Brief of Light Waves

Visible light is the range of light in the electromagnetic spectrum that can be seen by the human eye. The electromagnetic spectrum consists of all the electromagnetic radiations that exist in our environment. This includes gamma rays, x-rays, ultraviolet rays, infrared light, visible light, radio waves, and microwaves. The visible spectrum for humans ranges from the wavelength of 380-740 nm. A nanometer is a billionth fraction of a meter, which means that there is a very small window of the electromagnetic spectrum that is visible to the human eye. Since our planet is rich and abundant in diversity with various species with different anatomies, there are animals who can see various other portions of the electromagnetic spectrum. For example, Honeybees can see light in the ultraviolet spectrum, while snakes can see infrared light. 

In humans, the wavelengths of visible light are associated with colour perception, while the amplitude of a wave is associated with the brightness of the light. The larger the amplitude of a wave, the brighter it would appear to the human eye. In a rainbow, when white light is refracted in seven different colours, the light with longer wavelengths is perceived as red by the human eyes, the intermediate wavelengths appear to be green, while the light with the shortest wavelengths is seen in the shades of blue. 

White light = Violet, Indigo, Blue, Green, Yellow, Orange, Red (mentioned in the order of shortest to longest wavelengths).

Brief of Sound Waves

Just like light waves, the various components of a wave are associated with the human perception of sound. The pitch of a sound wave is determined by its frequency. High-frequency sound waves sound shrill or high-pitched to the human ear, while the low-frequency sound waves appear to be low-pitched or deep in nature. The audible range of sound frequencies for humans ranges from 20 – 20,000 Hz. Most humans show heightened sensitivity to sound waves that fall in the middle of this range. 

As you may have noticed, the training whistle used for dogs can’t be heard by humans at all, however, it alerts the dogs at one go. How is that possible? That is possible because dogs can hear the sound waves from the range of 70-45,000 Hz. Due to a higher range of frequencies exhibited by them, dogs are much more sensitive to sound than humans. 

Apart from this, cats also show excellent sensitivity to sound waves due to their broad range of frequencies. They can hear sound waves in the range of 55 Hz – 79,000 Hz, which is even broader than dogs. 

The loudness of a sound is based on the amplitude of the sound wave. The higher the amplitude of a sound wave, the louder the sound would be. The loudness of a sound wave is measured in decibels (db), which is the unit of measurement of the intensity of sound waves. A typical conversation happens at around 60 db. However, sound waves ranging from 80-130 db can be fatal and cause hearing damage. 

Even though amplitude is associated with the loudness of the sound, there are certain interactions between the frequencies and amplitudes that result in unique phenomena. For example, a 10 Hz sound wave will be inaudible to the human ear, despite a larger amplitude. Similarly, a 1000 Hz sound wave might be audible to the human ear even when it has a very low amplitude. 

Practical Examples of Waves in our Everyday Life

• X-rays: X-rays are well known for revealing the bone structure of a human body by permeating through the skin surface. From spotting fractures to killing cancer cells. X-rays have various applications in real life. X-rays are an example of transverse waves. Most X-rays have a wavelength ranging from 10 nanometers to 10 picometers, which allows them to visualize much smaller structures as compared to what can be seen under a conventional optical microscope. 

• Radio Waves: Radio waves are an example of transverse waves and exist as a series of repeated crests and troughs. These waves have the longest wavelengths in the electromagnetic spectrum ranging from 1 millimeter to over 100 kilometers. These types of waves are extensively used in radio transmissions, air-traffic control, remote-control toys, artificial satellites, etc. 

• Microwave: Microwaves are a type of electromagnetic radiation which have a wide range of applications. They are used in microwave ovens to cook food, in radars and communication devices, etc. Microwaves have a wavelength that ranges from 1 millimeter to 1 meter. 

• Acoustic Microscopy: Acoustic microscopy involves the use of longitudinal waves to penetrate solid objects to reveal their internal features such as cracks, voids, and fissures. This type of technology uses very high-frequency ultrasound wav
  es which usually have a wavelength of 1.9 centimeters or less. 

• Sonography: Sonography uses ultrasound waves to create images of internal body parts such as tissues, muscles, joints, and internal organs. The sonograms, also known as ultrasound images, are formed by transferring ultrasound waves into tissues using a probe, which results in a real-time image formation. 

Wave Equation

The wave equation is the mathematical expression between the speed, wavelength, and period of time. A wave is generated when a disturbance is caused to a particle in a medium. This leads to the creation of a wave pattern that moves from particle to particle in a medium. The frequency of each particle is equal to the frequency of vibration of the source particle ( the first particle where the disturbance was caused). Likewise, the period of vibration of every particle is equal to the period of vibration of the source particle. In one period, the source particle moves in a wavy motion: from the rest position to upwards, back to the rest position, from the rest position to downwards, and then back to the rest position. This back and forth movement leads to the completion of one wave cycle. 

Therefore, we can say that by the time one period has elapsed, the wave travels the distance of one wavelength. Now combining this information with the pre-existing knowledge of the equation of speed, which is speed = distance/time, we can derive the speed of the wave, which is 

Speed = wavelength / Period…………….(1)

As already mentioned above, the frequency is calculated in the units per second. This means period is the reciprocal of the frequency. Therefore, 1 time period would equal 1/f. 

Substituting the values of the period in the equation (1) with this information, we get the new equation, 

Speed = wavelength x frequency 

This above-mentioned equation is known as the wave equation. A wave equation is the mathematical expression of the relationship between speed, wavelength, and frequency and is used to analyze the motion of the waves. 

Wavelength and its Unit

Wavelength is the length of a wave from the highest point of a crest to the highest point of the adjacent crest or the lowest point of a trough to the lowest point of an adjacent trough. It is denoted by a symbol called Lambda (λ). As per the given definition, we know that wavelength is the length thus the S.I unit of wavelength should be the same as the S.I unit of length. We know, the S.I unit of length is a meter so the SI unit of wavelength is also a meter.

 

Definitions of Metre:

Meter Can be Defined in Different Ways:

• In terms of prototype meter bar: To maintain the new metric standard of length ‘The International Bureau of Weights and Measures’ constructed and preserved a prototype meter bar. This bar is made up of alloy (90% platinum and 10% iridium). One meter is the distance measured between two lines on this bar at zero degrees. In other words, the length of this bar is taken as 1 meter.

• In terms of the Distance between Latitudes: Meter is one ten-millionth of the maximum distance between the Equator and the North pole. The distance between the equator and the North pole is 10,000 km. The unit Kilometre is derived from the meter. Kilo means 1000 times thus 1 kilometer is equal to 1000 meters.

• In terms of Light: One meter is the distance traveled by light in a vacuum in 1/299,792,458 seconds. A meter is measured by the speed of light because 

1.  It remains constant everywhere.

2.  It can be measured from anywhere in the world to get an accurate and same result.

 

Other Units of Wavelengths:

As discussed earlier the SI unit of wavelength is meter. Some wavelengths are short and some are long. Even to solve different numerical problems the larger and the smaller units length was required. Thus we use exponential powers of 10 to measure the large property whereas the negative exponential is used for the measurement of shorter wavelengths.

Examples-

Submultiple Units: decimeter, centimeter, millimeter, etc

Multiple Units: decameter, kilometer, gigameter, etc.

Below is the table showing the relation of a meter with its multiple and submultiple units.

 

Multiples & Submúltiplos of SI Units – The Metre

 

The Relationship Between Wavelength and Frequency

Wavelength is the length of a wave and frequency is the number of waves. Thus in a unit area, if the length of a wave increases then its frequency decreases, and if the length of a wave decreases then its frequency increases. This means that the wavelength and frequency are inversely proportional to each other.

Since the frequency of waves are measured in large units so wavelength (because it is inversely proportional to frequency) is measured in smaller units.

 

Wavelengths of Different Waves in Metres

Gamma Rays: The wavelength of gamma rays is the shortest. It is less than 0.001 nanometer or 10-12 meters.

X-rays: The wavelengths of X-rays are in the range of 0.001 – 10 nm.

Ultraviolet: The wavelength of ultraviolet rays is in the range of 10 – 400 nm.

Visible Light: The wavelength of visible ligh
ts is in the range of 400-700 nm.

Infrared: The measure of the wavelength of infrared rays ranges from 700 nm to 1 mm.

Radio Waves: The wavelength of radio waves is the longest. It is longer more than 1 millimeter or 0.001 meters.

Practice questions based on Wavelength 

For a proper understanding of wavelength, let’s take a look at some of the practice questions based on the wavelength and frequency of a wave.

1. A radio station broadcasts at a frequency of 98, 400, 000 Hz. If the broadcast is an electromagnetic wave, then what would be the wavelength, if the speed of light is taken as c= 3 x 108 m/s. 

Answer: The relationship of the wave is denoted by the equation ƛ = c/f, where, 

ƛ= wavelength of the wave,

c= speed of light,

And, f = frequency of the wave. 

Substituting the given values to this equation leads to the following calculation:

ƛ = 3 x 10^{8} m/s / 98, 400, 000 Hz. 

  = 3.04 m. 

2. A note is played on the violin at a frequency of 445 Hz. If the speed of sound in the air is 345 m/s, what would be the wavelength of the sound?

Answer: the relationship between velocity, wavelength, and frequency is expressed by the equation of 

ƛ = velocity/ frequency.

Putting the values in the above mentioned equation, we get, 

ƛ  = 345 m/s / 445 Hz. 

= 0.77 m. 

Conclusion

experts have covered all points and different features of Unit Wavelength. Students can use these solved examples to get practical knowledge.

Uses of magnets in daily life can be found in numerous electronic devices, including television, radio, microwaves, hard disks, motors, generators, and many more. 

Magnets are divided into two types: permanent and temporary. The uses of magnets in everyday life vary depending on their type. 

What are Permanent Magnets?

Materials that generate a magnetic field within their internal structure and do not rely on electricity to retain their magnetism are permanent magnets. 

What are Temporary Magnets?

Many materials have the ability to inherit magnetic properties temporarily when in proximity with other magnetic materials, but these fade quickly, returning the material to its original nonmagnetic state. A magnet that loses its magnetic attribute once the permanent magnetic field or electronic current is removed, is a temporary magnet. 

Let’s understand what the practical uses of a magnet in our everyday lives are.

What are the Properties of a Magnet?

Every magnet, irrespective of its size or shape, has two different poles – the north pole and the south pole. The magnetic property of these two poles is more than the rest of the magnet’s body, which means that the magnetic property is maximum in these areas.

Here are three main properties of magnets:

1. Attractive Property: Magnet attracts ferromagnetic materials like iron, nickel, cobalt, among others. Additionally, magnetic poles with opposing magnetic fields attract one another.

2. Repulsive Properties: Property of repulsion and attraction exists between two magnets. Like magnetic poles repel each other. 

3. Directive Property: A magnet, suspended freely, will always point in a north-south direction.

What is the Use of Magnets?

The two types of uses of magnets in daily life are:

• Electromagnets

• Permanent magnets 

Uses of Electromagnets 

Electromagnets are temporary in nature as they only work under the influence of applied electric current. It is made from a coil of wire which behaves as a magnet when an electric current passes through it. An electromagnet is often wrapped around a core magnetic material like steel to enhance the magnetic field produced by the coil.

The strength of the magnetic field of these magnets can be altered by varying the power of the electric current. One can also change its polarity by altering the direction of the electric current. 

For example, the method of magnetic separation is used to separate magnetic substances like steel and iron from waste material. The crane’s long arm is fitted with an electromagnet. When the electromagnet is switched on and the arm is lowered over the heap of waste, the old iron and steel objects present in the waste get attracted to the electromagnet and stick to it. 

Electromagnets are Also Used in the Following: 

1. Generators 

2. Motors

3. Transformers

4. Electric buzzers and bells

5. Headphones

6. Loudspeakers

7. Relays and valves

8. Data storage devices: VCRs, tape recorders, hard discs

9. Induction cooker

10. Magnetic locks

11. MRI machines

12. Particle accelerators

13. Mass spectrometers

We also find the use of electromagnet in other processes like joining two bogies of a train, in a crane (JCB) used to transport heavy materials and waste, and in-service centers and garages to lift heavy vehicles, etc.

The theory of electromagnetism applies to the following domains: 

• Electrostatics

• Magnetic fields of slow and steady currents

• Motional e.m.f. and EMI

• Maxwell’s equations

• The propagation and radiation of EMW

• Electric and magnetic properties of matter

• Laws of conservation

Uses of Permanent Magnets

Permanent magnets are made of materials that inherit the magnetic field, and so the strength of the magnetic field cannot be altered. 

These magnets cannot be demagnetized, unlike electromagnets. 

So its uses can be found in devices like electric motors, magnetic recording and storage media, decorations, among others, where these properties are required. 

For example, a small coil of wire and a permanent magnet inside a speaker transforms the electronic signal to sound vibrations. 

A magnetic compass uses the directive property of the magnet. A compass has a magnetic needle that is pivoted from the center and suspended freely so it can rotate. The needle of the compass when suspended freely will always point in the north-south direction. This compass is used by soldiers, sailors, hikers, etc. 

Magnets are also used to hold objects like box lids, magnetic stickers, the doors of the refrigerator or cupboards, etc.

Permanent Magnets are Used in the Following:

1. Speakers

2. Headphones/earphones

3. Mobile phones

4. Cars

5. Generators

6. Television

7. Transducers

8. Hard drives

9. Sensors

Practical Uses of Magnets

A. Electromagnets

1. Home Appliances

Most of the electric appliances that we use in our homes work on the basic principle of electromagnetism. Some uses of electromagnets in a home include the following:

1. Electric fan

2. Electric doorbell

3. Induction cooker

4. Magnetic locks

So, how is a magnet used in an electric fan and doorbells?

In an electric fan, the EMI keeps the motor rotating, which in turn makes the blades of a fan rotate. 

However, in an electric doorbell, when we press the button, the electromagnetic force of the coil gets energized and the bell makes a sound.

2. Medical Equipment

An MRI or magnetic resonance imaging lets your doctor see the organs, bones, and tissues inside your body without having to do surgery. MRI works on the principle of electromagnetism, employing powerful magnets that produce a strong magnetic field. 

3. Memory Storage Devices 

The data or information in electronic gadgets and phones are stored in the electromagnetic format in the form of bytes and bits. 

4. Computer Hardware

Computer hardware also has a magnetic tape that works on the electromagnetism principle.

5. Communication Devices and Power Circuits

Without electromagnets, the mobile phones we use to communicate with people around the world could not have taken place. The electromagnetic pulses and the interaction of the communication signals make mobile phones and telephones very handy.

6. Others

In devices like electric fans, electric bell, telegraph, debit cards, credit cards, etc.

Did You Know?

In the olden days, electromagnets were mostly used in the data storage of VCP and VCR.

B. Permanent Magnets

There are endless uses of permanent magnets. Some practical uses of the magnet are:

1. Door magnets: Magnets are used to hold objects so they don’t shut on their own, like refrigerators, boxes, and containers, cupboards, etc.

2. Magnetic name tags 

3. Magnetic jewelry

4. Magnetic clasps

5. Magnetic water treatment: A method of passing hard water through a magnetic field to reduce its effects. It is a non-chemical alternative.

6. Magnetic filter

7. Adhesive magnets

8. Magnetic pickup tools

9. Magnetic knife holder

10. Magnetic tray

11. Compass

12. Magnetic toy

13. Maglev train

14. Induction cooker

15. Telephone

16. Cell phone

17. Clocks

18. Scientific instruments

The other three uses of permanent magnets are:

1. Refrigerators

One of the most important uses of permanent magnets is found in closing the door of a refrigerator. The gasket of the refrigerator that seals the door closed, has a thin inner magnetic strip, which is a permanent magnet.

2. Automobiles

Hybrid and electric vehicles use powerful permanent magnets. Magnets used in these automobiles are made of materials with a high proportion of rare earth permanent magnets, which are both expensive and in limited supply. 

3. Jewelry

Jewelry like bracelets, earrings, necklaces, and beads are made of permanent magnets because these magnets help in keeping jewelry clasped closed.

Do You Know?

Permanent magnets are also used in tools like screwdrivers? Screw drivers attract the screws. They are handy when dealing with small screws or hard-to-reach places.