Category: Physics Notes PPT

Introduction to Heat

We are quite familiar with the term heat that can be described as feeling too hot or too cold.

We know that the sun is the main source of the earth’s heat.

Only a fraction of the sun’s heat reaches the earth which is sufficient for life to exist on earth.

What happens if the intensity of sun rays reaching the earth increases?

We would start feeling hot and prefer to stay at home and sit under the AC.

Now, the question arises why we feel hot outside and cold under the AC?

So, the chill we feel is because of the flow of heat.

What is Internal Energy?

We know that temperature is the measure of the molecular kinetic energy of the particles in a system.

This kinetic energy is distributed amongst the translational motion, rotational motion, and vibrational motion of a molecule.

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There is also molecular potential energy by the electromagnetic force acting upon the atoms of an individual molecule and between each separate molecule.

The sum of all these energies exhibited by the particles of a system is called the internal energy of the system denoted by the letter U.

This energy is associated with atomic motion and is directly proportional to the temperature of the system.

So, higher is the temperature, higher is the internal energy, and vice versa.

What is Internal Energy of a System?

The internal energy of a system can be increased by increasing the heat transfer, but because of factors such as surface deformation, friction, there may be some energy loss.

We learned that for a particular system, there will always be a conservation of energy.

Let’s say, a stone is falling freely under gravity, it possesses both potential energy and kinetic energy.

So, let’s add internal energy of the objects to this list, and restate conservation of energy with the equation below:

                                     ΔPE +ΔKE +ΔU = 0

Here,   ΔPE = change in potential energy

            ΔKE = change in kinetic energy, and

            ΔU = change in internal energy

So, if any of these quantities change, then some energy is transformed from one form to another.

Internal Energy Formula

Consider an ideal gas:

Its total energy = Internal energy because of the kinetic energy of molecules.

Its potential energy is zero because there is no attraction between the molecules.

So, TE = 0 + KE

Using the First Law of Thermodynamics

Consider a thermodynamic system having an ideal gas packed under the piston:

On adding Q amount of heat to this system, several factors of gas increments:

1. Molecular speed 

2. Heat and temperature

3. Pressure

The piston moves upward; it means some work is done by this thermodynamic system to bring the piston up.

Here, this thermodynamic system absorbs heat. It retains a part of heat with itself and uses another part by working in raising the piston.

The part of heat absorbed by the system increases its internal energy.

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The internal energy was U1 after piston rise; the internal energy is U2 and U2 > U1.

So, the change in internal energy is:

ΔU = U2 – U1

Here, ΔU is the heat retained by the system, and 

W  = The work done by the system to raise the piston.

So, Q (Amount of heat provided) = ΔU + W

Why the system kept ΔU instead of U2?

Because the heat absorbed by this system got converted to the work done in raising the piston and only a difference of the energy got by the system.

This is how we got the formula, Q = ΔU + W.  

In differential form:

                     მQ = მU + მW…..(1)

Relation Between Enthalpy and Internal Energy

We define enthalpy as the heat content of a system at constant pressure.

We know that: H = U + PV

This relationship says:

Heat content in the system is equivalent to the internal energy of molecules or atoms (PE + KE) at quantum level + PV (the work done to establish the system at external pressure P and volume V from space.

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So, work done can be seen in this diagram.

The unit of enthalpy is KJ/mol. 

In thermodynamics, H has no significance; let’s understand why?

If we go at the microscopic level to estimate the amount of energy each molecule possesses, it becomes an impossible task to do so.

Like we can’t measure the quality of a person like singing but can compare by the number of awards you won (Quantifying). Similarly, we can’t measure the energy absorbed by the system.

Therefore, to consider H as an enthalpy, it becomes a matter of confusion.

So, that’s why we study ΔH in place of H.

So, ΔH and ΔU instead of H and U.

Since the volume expanded from V1 to V2

At constant pressure equation becomes:

 ΔH = U + P (V2 – V1) 

 ΔH = U + PΔV

At constant volume: ΔH = U + VΔP…(2)

Pascal or kilopascal is a derived unit of pressure. In physics units and conversion of units is an important part of the learning. Kilopascals are shortened or abbreviated to kPa with a lower case k, an uppercase P and a lowercase a. Kilo means one thousand hence there are one thousand Pascals in a kilopascal. The pascal (a symbol used is Pa) is the SI derived unit of pressure or stress (also for modulus of elasticity like Young’s modulus and tensile strength). 

The unit of the pressure of the pascal is equivalent to one newton per square metre (N/m²). In our day to day life, the pascal is most frequently used in the form of kilopascal (1 kPa = 1000 Pa). One kilopascal corresponds to about 1% of atmospheric pressure with reference to the sea level.

kPa

The conversion of units is an important concept in physics. We know that a pascal is a derived unit of pressure. Pressure is defined as the normal force exerted by a fluid per unit area. The concept of pressure is used mainly while discussing liquids and gases. The counterpart of the pressure in solids is normal stress. Now lets us have a look at how a pascal is derived.

According to the definition of the pressure we have,

⇒ Pressure =
[frac{Force}{Area}] = [frac{N}{m^{2}}]  ………..(1)

Force is expressed in Newton’s and the area on which the force F exerted is expressed in m².Therefore pressure is expressed in terms of N/m2known as the Pascal in general.

Therefore We Write,

1 Pascal = Newton meter^-2 =1 Nm^-2…….(2)

The unit of pressure pascal is too small for most of the pressures encountered in our everyday lives. Therefore we use multiples of pascals such as kilopascal, megapascal etc….

In kilopascal, we will be having one thousand Pascals. We know, a kilo is an abbreviated form of 1000. Similarly in megapascal, we will be having 106pascals. Mathematically we write,

⇒1 k Pa=103 Nm^-2= 1000 Nm^-2

And,

⇒1 M Pa = 106 Nm^-2

Kilopascal To Psi

The pressure can also be measured in terms of Psi, bar. Therefore we can have unit conversions such as the conversion of Kilopascal to Psi, pascal to Psi, Psi to the bar, Psi to kPa, etc. Let us have a look at the conversion of kilopascal to Psi (pound squared inch). In the English system, the pressure is measured in terms of the Pound force per square inch which is abbreviated as Psi in general. One atmospheric pressure is equal to 14.696 Psi. 

Now, the relation between kilopascal and Psi is given by the formula:

⇒k Pa= 0.145 Psi and 101.325 kPa=14.7 Psi

Similarly, we can write,

⇒1Psi = 6.89 kPa

This is the required formula for converting kilopascal to Psi. These conversion techniques can be mastered after having thorough practice and solving numerical. Let us have a look at a few numerical problems for better understanding.

Examples

1. Convert 130 Kilopascal to Psi.

Sol: Given, we have a pressure exerted by some fluid or gas is 130 kPa. We are asked to determine 130 kPa in terms of the Psi.

We know that,

⇒1 k Pa= 0.145 Psi

Therefore, we write:

⇒130 k Pa=130×0.145 Psi=18.85 Psi

Thus, 130 kilopascal is equal to 18.85 Psi.

2. Convert 50 Psi to Kilopascal.

Sol: Given, we have a pressure exerted by some fluid or gas is 50 Psi. We are asked to determine 50 Psi in terms of the kPa.

We know that,

⇒1Psi = 6.89 kPa

Therefore, we write:

⇒1Psi = 6.89 kPa

⇒50 Psi = 50  x 6.89 kPa=344.5 kPa

Thus, 50 Psi is equal to 344.5 kPa.

3. Convert 122 Kilopascal to Psi.

Sol: Given, we have a pressure exerted by some fluid or gas is 122 kPa. We are asked to determine 130 kPa in terms of the Psi.

We know that,

⇒1 k Pa= 0.145 Psi

Therefore, we write:

⇒122 k Pa=122 x 0.145 Psi=17.69 Psi

Thus, 122 kilopascal is equal to 17.69 Psi.

4. Convert 35 Psi to Kilopascal.

Sol: Given, we have a pressure exerted by some fluid or gas is 35 Psi. We are asked to determine 35 Psi in terms of the kPa.

We know that,

⇒1Psi = 6.89 kPa

Therefore, we write:

⇒1Psi = 6.89 kPa

⇒35 Psi = 35 x 6.89 kPa=241.15 kPa

Thus, 35 Psi is equal to the 241.15 kPa.

The neutral point of any electric supply you have is closely related to the earth; this is the reason that the neutral point and the earth point are closely related too. But remember, that they are closely related but are not the same. Since they are closely related, students often get confused and think they are the same. 

Talking about earthing point and neutral point, they have closely related anchors and in almost all the wiring systems, you are going to find these points. They both are an essential part of the wiring of an appliance and are used for safety purposes so that the user remains protected from the electric current. We know that there are frequent fluctuations that occur in electricity or equipment and if you have these points in the appliance, there is less chance for your appliance getting any kind of damage.

To understand what is earthing and neutral point, we will look at a three-pin electrical socket that we use in our everyday life. The current that is supplied for a household is carried by a three-phase circuit. That is the reason every socket used for any electrical equipment is preferred to be three-pin. The three pins correspond to earth, neutral, and phase. The phase line is the one that carries current, the neutral line provides the return path to balance the flow of current, and finally earthing is purely used for safety purposes.

Below in this article, you are going to get information about the earthing and neutral separately and then we are going to get the information about their differences in brief. For all those who are looking for an article that can explain to you the topic of earthing and an article in brief within a short time and in an effective way, then this article, provided to you by , is going to help you. Use this article to revise your topic in a short period of time.

What is an Earthing?

Earthing, from a physics point of view, is the process of immediate transfer of electric energy into the earth. This process of earthing is always done with the help of a low resistance wire so that minimum resistance is provided to you while you are transferring the charge to earth.

Basically earthing is a precautionary connection that is made in many high-voltage devices and those devices that are costly as well as fluctuations on which can easily damage the device, such as that of air conditioners. We are provided with this earthing connection so that due to excess fluctuations in the devices, they may not get damaged. 

If we talk about the main function of earthing, it is to protect humans from getting any kind of electric shock. Any electric equipment, when it comes into contact with a metal surface, a current is induced in it which results in electric shock. So in order to protect you from getting shocked while using them, earthing is done. Besides this, earthing provides you with a low resistance path, so that the extra current directly travels down to the ground.

Neutral

The neutral wire is used for providing a return path for the flow of current in an AC circuit. The neutral wire carries no current, yet without neutral wire the AC circuit is incomplete. In any electrical circuit, the neutral wire will redirect the path of the electrical current to its source point. 

Basically, this neutral wire or neutral point in a three-phase circuit is where the sum of current will be zero and this neutral point is most commonly known as the zero potential point. In an AC circuit, the earth and the neutral point must be at the same potential, ideally, the potential difference between the two will be zero.

The major resemblance that you can see between both neutral connections and earthing connections is that both of them are used for safety purposes.

Earthing and Neutral – Their Differences

These are the major earthing and neutral differences. The difference between ground earth and neutral provides a brief idea of  AC circuit connections.

Importance of Earthing

• The discovery of electricity has made life easy and convenient. As every discovery has its own pros and cons, the cons of electricity were electrical shocks that may lead to death. 

• To prevent the electrical shock the earthing concept was introduced. 

• The Earth wire is a conductor embedded in the ground and electrically in contact with it. Earthing prevents wastage of electricity and electrical shocks.

• There can be electricity overload in the circuit and if you have this neutral and earthing connection, then you will be protected from the electric shock or overloading of electricity in the appliances.

Importance of Neutral

• A neutral wire is half of the electrical circuit. It completes the AC circuit.

• A neutral wire is required to return the electric current to its source point, a circuit without a neutral wire will not conduct.

• A neutral wire can directly carry the circuit to the original powerhouse. More preferably, if we say then this brings the circuit back to ground connected at the electric panel.

Physics is that one field of education where we can see what is happening, meaning the results, and the examples are macro, and we can see them in our daily lives. One of the major concepts of physics revolves around the charge, which is stored in a given body. When you come across a charge in your physics book, you know things are going to get serious from this point onwards. Don’t worry, and we will help you learn everything about the conservation of charge and its real-world example so that you can get a better understanding of the concept. 

Charge in physics is what atoms, protons, and electrons are to chemistry, it is the base of electronic physics. Everything you see, from your computer, TV, to your washing machine runs on the conservation of charge, and today we are going to break down this concept. 

Law of Conservation of Charge

Now let’s define the conservation of charge. It states that a positive charge present in the given body will always have the same amount of negative charge to keep the body in a neutral state. These types of bodies are called the neutral body, and you can’t say they don’t charge them, as they have both negative and positive charges in equal portions to cancel them out. As a result, we concluded that a charge in a given body could not be created, nor could it be destroyed. We can only transfer it from one system to another, and the material that provides transfer of charge is called conductors. From conductors, a charge can be displaced in the form of heat or the displacement of electrons. This is what the law of conservation of charge is in physics. 

What is Conservation of Charge?

There are two ways in which a body can leave its neutral state of charge.

A given object will get a negative charge if the electrons get transferred to it from another source. 

Let’s take an example here, and we take a negatively charged rod with a net charge of -4e. When this rod touches the surface of a neutral body, which is a conductor, displacement of the electron takes place from the rod to the neutral body. This is because electrons are repulsive to each other, and they want to spread in a wider area to get away from each other, after the transfer of charge we have -2e and -2e on the rod and the sphere respectively. 

The total charge in the system was -4e, and after the transfer, it remains -4e, but now it is divided into two bodies. That’s how a body gets a negative charge. 

An object present in the neutral charge state will get a positive charge when the electrons present inside of it, get transferred to another body. 

We take a rod that is positively charged, and we touched the surface of the neutral body with the rod. During this process, electrons present in a neutral body are attracted to the charge present in the rod, and thus, they are displaced from the neutral body to the rod. As a result, what we have left is a body that has less negative charge than its positive charge making it a positively charged body.

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Here we have a +4e charge present in the neutral body when the transfer of the electrons took place, and we are left with a +2e charge on the rod and a +2e charge on the body. So the object becomes positively charged, and the protons that were present in the body remain the same. Here once again, we have seen the conservation of charge.  

State The Law of Conservation of Charge

The net charge present in the isolated system will always remain constant; thus, the given system will not be doing any exchange of mass and energy with its surrounding atmosphere and will never charge that is different from its initial state. This is what the law of conservation of charge is according to physics. 

Conservation of Charge Examples

Let’s take one example here, and you might have seen an old trick of comb and hair, where your hair rises and sticks to the comb. It might look like magic, but it comes in the simple conservation of charge examples. Your hair is here in a neutral state, having both positive and negative charges in an equal amount. A combination has a positive charge, and when you use it, it takes away the positive charge from your hair and leaves it with a negative charge. 

Thus, the negative charge starts to repel each other, and you will have yourself floating hair in the air.

It is a form of energy which makes objects visible as we cannot see objects in darkness.During day time sunlight acts as a source of energy which makes everything visible whereas at night we use artificial sources of light for seeing objects. As when light falls on an object, light gets reflected and this reflected light comes to us which makes the object visible. An object which is known as a source of light. Some common examples of sources of light are sun, bulb,etc. Sun is the universal source of light. It is approx 1500 km away from us then also it brightens all universe.

Natural and Man Made Source of Light

Natural Source of Light: Source of light which is already present in nature known as natural source of light. Example: Sun.

Man Made Source of Light: Source of light which is prepared by humans is known as man made source of light. Example: bulb, candle, torch, etc.

Classification of Object Based on Tendency to Produce Light

1. Luminous objects: An object which has a tendency to produce light are known as luminous objects. Example: Sun, bulb, etc.

2. Non – luminous object: An object which does not have a tendency to produce light known as a non-luminous object. Example: moon.

Propagation of Light

From the experiment below we will prove that light travels in a straight line i.e path covered by light is alway straight.

• For this, take a cylindrical tube; which can be easily bent.

• Try to see a source of light; like a bulb or a candle; through the straight tube.

• Once the tube is bent at some angle, it is not possible to see the source of light through it.

• This happens because light travels in a straight line.

Figure Showing Propagation of Light

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Types of Object

1. Transparent Object: An Object through which light is completely passed known as transparent object. We can clearly see through a transparent object.

2. Translucent Object: An object which allows partial passage to light is called a translucent object. We can see through a translucent object but the vision would be murky.

3. Opaque Object: An object which does not allow passage to light is called an opaque object. We cannot see through an opaque object.

What is the Shadow?

When a ray of light falls on an opaque object, a dark patch is formed on the other side of the object whether it is on ground or it is on screen present on the other side of the object. Three things are required for the formation of shadow, viz a source of light, an object and a screen. The size of shadow totally depends on distance between object and source of light. Closer the source of light, larger will be the size of the shadow. Far the source of light is, smaller is the shadow.

In case if the incidence angle is smaller, shadow is longer. On the same side if the incidence angle is bigger, the shadow is smaller. This concept is well proved with a smaller size of shadow in the evening and noon and bigger size of shadow in the morning.

Features of Shadow of an Object

1. Shadow is always in erected form.

2. It is always in real form.

3. Color of the shadow is always black.

4. It can be smaller than object, bigger than object or same size to object.

Light and its Reflection

Reflection occurs mainly on the mirror surface as incident light gets reflected when it falls on a clear surface and due to reflection the image formed is always erect.

Reflection

When a ray of light falls on a surface like glass which has shiny and glossy properties from where light gets reflected. This phenomenon of bouncing back of light is known as reflection.

During reflection angle of incidence is equal to angle of reflection.

Features of Image Formed Due to Reflection

1. Image is the same size and color as the object.

2. Real image is formed.

3. Right side of the object appears to be left in image and vice-versa.

Formation of Image in Pinhole Camera

Pinhole cameras consist of a closed box having a small pinhole in the front and having translucent screen at the back. Pinhole camera is made up of translucent butter paper. This is the reason we can see objects in a pinhole camera.

Uses of Pinhole Camera

1. It is used to view objects like trees and buildings.

2. It is also used to take photographs.

Principle

It works on the principle that light travels in a straight line.

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A wave that consists of a vibration or any periodic disturbance which happens in the same direction like the advance of the wave. When you compress one end of the coiled spring and release it, it experiences a wave of compression which travels to the length of it, stretching follows it. The coil of the spring has a point that moves with the wave and returns from the same path, while returning it passes from the neutral position and then again reverses its motion. Moving of the sound through air results in compressing the gas in the direction where sound waves are travelling while they vibrate back and forth. The seismic waves which are primary p, are also longitudinal. 

All the particles in the longitudinal wave, vibrates to its rest position which is normal and with the axis of propagation, and all the particles that participate in the wave motion behaves in the same way, except in phase of vibration, there is a case of progressive change that means every particle finishes its cycle of reaction at a time that is later. With the combined motions, it results in moving forward in the alternating region of compression and rarefaction towards the propagation’s direction. 

The pattern of disturbances is of two types or in other words the formation of waves is done in two different methods. We know that the energy of the particles in motion is transmitted in the form of waves. Depending on the type of motion two forms of waves are classified, the first one is a longitudinal wave and the second is a Transverse wave. The longitudinal motion or the longitudinal wave are found when the energy has to be transmitted within the medium. Whereas the transverse waves are formed at the surface. 

Terms Used in Longitudinal Waves

• Crest – a point on the medium which has the maximum amount of positive or upward displacement from the position of the rest, that is known as the crest of the wave. 

• Trough – it is just the opposite of crest. The point on the medium which has the maximum amount of negative or downward displacement from the position of the rest, that is known as the trough of the wave. 

• Amplitude – when the particle on the medium from the position of rest has a maximum amount of displacement, it is termed as the amplitude of the wave. The distance from the rest to the crest in a way is the amplitude. The amplitude can be calculated from the position of the rest to the position of the trough. It can also be calculated like the distance of the line segment which is perpendicular to the position of the rest and moves vertically upward from the position of the rest towards point A. 

• Wavelength – the length of one full wave cycle is the wavelength of a wave. When a pattern is repeated, it is known as a wave. The pattern repeats itself in a regular and periodic way over space and time both. It can be calculated per the distance between crest to crest or can be calculated from trough to trough. 

Examples of Longitudinal Waves

The longitudinal waves are mechanical waves and these are readily used in nature for transmitting energy from one point to another within the medium. There are several examples of longitudinal waves. Sound waves are the most common example of longitudinal waves, pressure waves, spring waves, etc… Let’s have a look at these examples in detail to understand the concept of longitudinal waves.

The best example of longitudinal waves is the sound wave, in order to receive the sound wave we definitely require a medium which is generally an air medium. This is the main reason why the sound waves can not propagate in a vacuum. In this article, we will discuss what are longitudinal waves, examples of longitudinal waves, formation of longitudinal waves, etc…

1. Sound Waves in the Air:

Yes, the sound waves are longitudinal in nature. When we speak, the sound wave propagates through the air medium and reaches the audience. The sound waves are the best example of a longitudinal wave and are produced by vibrating or disturbing the motion of the particles that travel through a conductive medium. An example of sound waves in a longitudinal direction of propagation is the tuning fork. In sound waves, the amplitude of the wave is always the difference between the maximum pressure caused by the wave and the pressure of the undisturbed air. The propagation speed of sound depends upon the type, composition of the medium, and temperature through which it will propagate.

2. The Primary Waves of an Earthquake:

It is said that animals can sense earthquake waves much before humans. They have the ability to sense the seismic P waves, which travel only in the interior of the earth. Even humans can experience a little bump and rattle of these waves, but they are mostly unnoticeable to us. The P waves are the fastest waves, and they require a medium to travel either solid or liquid. The P waves cause the interior of the earth i.e., tectonic plates to move back and forth (in other words to oscillate)  in a longitudinal manner, which leads to the surface waves i.e., seismic S waves, which we can feel.

3. The Vibration in a Spring:

Consider a small spring, suppose we knock the end of the spring, the waves that formed will flow through the spring. The waves formed will propagate within the spring and hence they are considered to be the longitudinal waves. At the same time, if one end of the spring is fixed, the waves will propagate in the up and down direction resulting in transverse waves.

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4. The Tsunami Waves:

We know that tsunamis are dangerous natural disasters that may lead to severe loss to human beings. Tsunamis cause damage to coastal regions (sea shore) and that’s the reason why people residing in coastal regions are afraid of them. Most people think that sea waves are transverse waves as they keep travelling in to and fro motion i.e., they go up and down continuously. However, water or sea waves, including Tsunami, are an example of both transverse as well as a longitudinal wave. When the waves reach the shore or remote areas, they become comparatively smaller and thinner, and water molecules move parallel to the wave, hence making it a longitudinal wave.

Transverse and Longitudinal Waves:

Let us understand what are transverse and longitudinal waves with the following list of differences. Both the longitudinal and transverse play an important role in elaborating the concept of sound. Thus the major difference between the transverse wave and longitudinal wave are as follows:

 

Did You Know:

Dogs are sensitive to sound at a higher frequency than humans, allowing them to hear noises that humans can not.

Sound waves are used by many animals to detect danger, warning them of possible attacks before they happen.

Sound can not travel through a vacuum (an area empty of matter), it requires a medium.

The speed of sound is around 767 miles per hour.

The loud noise you create by cracking a whip occurs because the tip is moving with a high frequency and speed it breaks the speed of sound.