Category: Physics Notes PPT

The electrical circuit or the electric circuit is an interconnection of electrical components to perform a specific function. These circuits use two types of power, one is alternating current and the other is direct current. The AC current is generated by power stations and is used for large devices whereas the DC current is used for batteries, machines, and electrical appliances. When this current is flowing through the devices, the power may increase or decrease suddenly. To protect that circuit breakers or fuses are arranged in series with the components to prevent damage to the whole circuit. Let us see what is the meaning of fuse and circuit breaker, what does a circuit breaker do?

What is a Fuse?

In relation to the electronics, the fuse is an electrical device that provides protection to the electrical circuit from the over current. It is called a sacrificial device because the fuse is a metal strip or a metal wire so whenever there is an overflow of current in the circuit, this strip melts and interrupts the current flow. When the fuse is damaged depending on the type used it must be replaced or rewired.

Some of the reasons for fuse operation are short circuits, device failure, mismatched load, or overload. It is used to remove the power automatically from a faulty device. In recent times, the fuses are sometimes replaced by a special device called circuit breakers. But significantly both share different characteristics.

Fuse – Construction:

We know what is the meaning of fuse, now let us see how it is constructed. A fuse consists of a wire or metal strip that has a small construction compared to all the electrical conductors. These are arranged in series in order to carry the current flowing through the circuit. Due to the current flow the resistance of the element liberates heat. When there is too much flow of current in the circuit then either the fuse will melt directly or the soldered part in the fuse will melt which makes the circuit open.

The fuse elements are made up of desired elements in order to provide stable and predictable characteristics, these elements are copper, zinc, aluminum, silver, or alloys. To increase the heating effect the fuse elements are shaped. The current is divided in between the multiple strips in case of large fuses. To avoid the strain on the fuse these are supported by steel or nichrome wires.

What is the Use of Fuse?

There are several reasons to use the fuse in the circuits, let us see what are they:

• These are used as safety for the electrical circuits.

• They are less costly.

• The reliability of the fuses is very good.

• As the age of the fuse increases, its speed remains the same.

• There is no necessary to maintain the fuse often.

• To have a high interrupting capacity it is not necessary to pay for the high premiums.

What is Circuit Breaker?

Circuit breakers are automatically operated switches that are specially designed to protect the circuits from damage. As its basic function is the same as that of the fuse it is not necessary to replace the circuit breaker with a new one, instead, they can reset by themselves or manually to continue performing its operation. The size may vary as they are made to protect the small household appliances from the large sitch gears that pass high voltage. The circuit breaker that removes the power from the faulty device is also abbreviated as OPCD – Over Current Protective Device.

Circuit Breaker – Operation

Let us see what do circuit breakers do? The circuit breaker first detects the fault. The detection in the low voltage circuit is done by itself. In the case of high voltage devices, a separate protective relay is been arranged, and hence for the operation of these relays, an extra power supply is required. Once the fault is detected, the circuit must open by removing the connection in between the contacts and this is done by the energy stored in the circuit breaker. The stored energy is such as the battery, or compressed air or the thermal expansion, or magnetic field. Once the contacts are removed, the small or miniature devices are discarded and in the case of high voltage circuit breakers or power circuit breakers, the contacts can be replaceable.

We have seen what is a fuse and a circuit breaker. Now let us look at the difference between,

Fuse vs Circuit Breaker

Types of Circuit Breaker:

1. Air circuit breaker.

2. Molded case circuit breaker.

3. Miniature circuit breaker.

Conclusion:

In the case of the power connection, the flow of electricity takes place through the circuit box. The fuse or the circuit breaker performs the same operation, they help the devices to protect the circuit from damage and they act as a switch. These can be operated manually or automatically. Once these are operated on the faulty devices they can either be replaced or sometimes they can reset themselves to continue the operation.

Energy and power are two terms that people often use interchangeably in daily life. However, when dealing with Physics, both of these differ in definition, scope and many other factors. Thus, understanding the difference between power and energy is crucial.

However, before proceeding to a detailed power vs energy comparison, let us learn a bit more about these two terms.

What is Power?

Power is defined as the rate at which a specific work is done and for which energy is transmitted. In essence, it refers to the consumption of energy per unit time.

Any object that transfers higher energy in a limited time can be termed to possess greater power. The SI unit of power is Watts, which is Joule/second.

Example of Differing Power

Suppose that A,B and C are the three mechanical machines which are equally efficient and are made to work on a particular set. Machine A, B and C  complete the same work in 20 minutes, 30 minutes and 40 minutes respectively.

Here from this example, we can say that machine A possesses more power in comparison to machine B and C as all three machines are having the same efficiency but machine A completes the same work faster than machine B and C.

What is Energy?

Energy refers to an object or an individual’s ability to do work. The amount of time that one can work defines their energy. Therefore, like power, time is a crucial factor when determining energy. In scientific terms, energy is transferred from one object to another. The SI unit of energy is Joules, which can also be expressed as watt-hour.

Energy can be Divided into Several Types, Such as – Heat

• Potential

• Kinetic

• Electric

• Mechanical

• Nuclear

• Light

Before venturing into the difference between power and energy, you should also know that there are only two sources of energy – renewable and non-renewable. Coal and petroleum are non-renewable sources, while wind and water are renewable energy sources.

Example of Energy

For instance, consider a bowler in a bowling alley. The bowling ball rolls toward the standing pins, and transfers its energy into the pins that it hits, thereby sending them flying. The bowling ball, on the other hand, acquires its energy when the bowler throws it on the lane.

To understand the difference between power and energy in physics, consult the table below.

 

What is the Difference Between Energy and Power?

Now you know the difference between power and energy. Take a look at the common formulas for calculating energy and power.

Take a look at the common formulas for calculating energy and power.

Calculating Power

• General Calculations – Power (P) = Work/time

• Standard Electric Power Formula – Power = Voltage x Current

• Electric Power in Resistors = I2R, where ‘I’ is the current and ‘R’ is the resistance.

Calculating Energy

• Kinetic Energy – K.E =  [frac{1}{2}]mv2, where ‘m’ is the object mass, and ‘v’ is its velocity.

• Potential Energy – P.E = mgh, where ‘m’ is mass, ‘g’ is the gravitational acceleration and ‘h’ refers to object height.

• Electric Energy – W = P x t, where ‘P’ is power and ‘t’ is time.

Watts is the SI unit of power, and Volts is the SI unit of potential difference.

When we go to the electricity shop, we find a 9 Volt battery, 9 Watts bulb, and so on. However, we come across a question as to why there are so many units like Watts, Volts, Ampere, etc. 

(Image to be added soon)

The units like Watts and Volts have a difference. 

Power is measured in Watts, while voltage in Volts. There is a difference between Watts and Volts. In this article, we will learn about the difference between Watts and Volts in a detailed manner.

Difference Between Watts and Volts

Now, let’s discuss the difference between Watt and Volt in tabular form:

Watts and Volts

What is Power?

The amount of work a body can do in a unit of time is called power. In simple words, power is the rate of performing any task.

The formula for power is :

                   Power = Work/Time

Thus the power of an agent measures how quickly it can do the work/job. When you take less time in doing any work, it means you have great power. If in case, you take a large amount of time to do the same work, it means you have less power.

So, power is inversely proportional to time. 

There are various formulas for power; these are:

1. V x I

In unit: Volts x Ampere

Volt-ampere is the apparent power.

2. W/t

In unit: Work/time

Joule per second

3. P = F . v

In unit: Force x velocity

N . m/s

What is Voltage?

Voltage is called the electric tension or the electrical pressure, which pushes charged electrons from one end to the other in a specified direction inside the circuit. 

On connecting the battery to the circuit, the potential difference develops across the two points of the circuit. The difference developed, leads to the pushing of an electron. 

So, the potential difference between the two points is measured by the amount of work done in moving a charge from one point to the other.

There are various formulas for voltage; these are:

1. P/I

In unit: Watt/Ampere

2. IR

In unit: Ampere x Ohm

3. W/q

In unit: Joule per coulomb

Difference Between Watts and VA

The below table lists the difference between Watts and Volt Ampere:

(Image to be added soon)

PNP is a Bipolar Junction Transistor or BJT in which holes are the major current carriers, while electrons are minor. The arrangement of the PNP transistor is in such a way that the P-type doped semiconductor is separated by a thin layer of N-type doped semiconductor material.

NPN is another BJT in which electrons are the major current carriers, while holes are minor. The arrangement of NPN transistor is in such a way that two N-type doped semiconductors are separated by a thin layer of P-type doped semiconductor material embedded between them.

Differentiate Between NPN and PNP Transistor

Do you know what is the difference between NPN and PNP transistor?

The basic difference between an NPN transistor and PNP transistor is indicated by the arrow of the current flow. If the current points outwards, it is NPN, and if the current points inward, it is an NPN transistor.

To understand in detail, let’s distinguish between NPN and PNP transistor in tabular form:

Distinguish Between NPN and PNP Transistor

PNP and NPN Transistors

PNP and NPN transistors are opposite in their functionality. When you apply current to the Base Junction of the NPN transistor, it allows more power to flow through it; that’s why NPN are considered good for amplifiers. However, the PNP does the opposite. When you apply current to the Base junction of the PNP transistor, it shuts off.

Both transistors function as a valve. If you turn it one way and the water (electricity) is able to flow, and if you turn it the other way, it does not. Both of the transistors make up the fundamental components of Logic Gates for processing digital signals in computers and other electronic devices.

The other places we use transistors are sensors, amplifiers, oscillators, detectors, modulators, and various electric circuits to perform functions.

Summary

So, we understood that both PNP and NPN transistors are current controlling devices where conduction is carried out by charge carriers viz: holes and electrons. When major carriers are electrons, it is an NPN transistor, and when there is a majority of carriers that are holes, it is a PNP transistor.

The rate of change of the electric displacement field is known as the displacement current. It is calculated in the same way as electric current density is calculated.

Maxwell’s Equation includes a term called displacement current. It was created to bring the Ampere circuit law into line with logic. Ampere (Amp) is the SI unit for displacement current.

This dimension can be measured in length units, which can be maximum, minimum, or equivalent to the actual distance traveled from start to finish.

Displacement current is an electric current created by a time-varying electric field rather than by moving charges.

Characteristics of Displacement Current

• Displacement current is another type of current apart from conduction current.

• As with conduction current, it does not appear from the actual movement of electric charge.

• It is a vector quantity.

• It is vital for electromagnetic wave propagation.

Maxwell’s Equation is a good way to explain displacement current.

Maxwell-Ampere Law and Equation

Electricity and magnetism are important aspects of physics. Because electricity and magnetism are intrinsically related, they are grouped as electromagnetism.

A current-carrying wire provides insight into electromagnetism. When an electric current flows via a wire, it creates a magnetic field around the wire or conductor.

This current, which travels through a conductor, is known as the conduction current. It is caused by electrons moving through a conductor. 

Since we learned about displacement current earlier, it is now important to note that displacement current is distinct from conduction current. Because displacement current does not carry electrons.

Now let’s understand the relationship between displacement and Maxwell Ampere law.

1. Ampere’s law was developed by Andre-Marie Ampere. It states that :

Here Maxwell gave an addition to Ampere’s law which resulted in Maxwell-Ampere Law.

2. James Clerk Maxwell, a famous physicist, well known for his work on Maxwell’s equations gave addition to Ampère’s law which stated that:

Equation of Maxwell-Ampere Law

Maxwell predicted that a time-varying electric field in a vacuum/free space (or in a dielectric) produces a magnetic field.

It indicates that a changing electric field causes a current to flow across a region. Maxwell also predicted that this current produces a magnetic field similar to that of a conducting current. “Displacement current” (ID) was the name given to this current.

The equation is:

[I_{D}=epsilon _{o}frac{dphi E}{dt}]

Where [phi E] is the Electric Flux

Maxwell also stated that when conduction current (I) and displacement current (ID), are combined, they have the property of continuity, even though they are not continuous individually.

Maxell was inspired by this idea and modified Ampere’s circuital law to make it logically consistent. Thereafter he stated revised Ampere circuital law which now is known as Ampere-Maxwell law.

From

[oint _{C}vec{B}.vec{dl}=mu _{o}(I+I_{D})]

[mu _{o}(I+epsilon _{o}frac{dphi E}{dt})]

Physics is an interesting and thought-provoking subject. Students should not have the habit of rote learning, rather they should study the subject with an open and fresh mind. Students should constantly keep profiling their minds and stay curious while learning the subject of Physics. 

The team of experts at has framed the teaching method in a fashion where they keep provoking the young minds to keep making them learn new concepts, to make them stay curious and open their minds towards the world of science. 

This particular topic explains one such concept of Physics for the students. This will help the students have a strong and easy grasp of the topic and also increase their scores in the exams. 

The Article Explains The Following Concepts – 

• What is Dulong Petit Law?

•  Dulong Petit Law Equation

• The Law of Dulong and Petit Formula

• Numerical problem with solution 

• Conclusion 

• FAQs

What is Dulong Petit Law?

In 1819, two french physicists, Pierre Louis Dulong and Alexis Petit, better known as Dulong and Petit proposed a thermodynamics law, which states the classical expression of Molar specific heat capacity.

 

According to the Dulong and Petit law, the gram-atomic heat capacity i.e. the product of the specific heat capacity and the atomic mass of an element remains constant. This law was then modified to apply to metallic elements only and now is used to calculate the approximation at intermediately high temperatures.

 

The modern theory, however built upon the assumption by Einstein in 1907, tells us that the heat capacity of solids is due to the lattice vibrations in the solids. But despite its simplicity, the Dulong and Petit law offers a good prediction for the heat capacity of many elementary solids at higher temperatures.

 

()

 

Dulong Petit Law Equation

Dulong Petit formula as given by Dulong and Petit, after numerous experiments showed that the heat capacity per weight for several elements was the same. The Dulong Petit derivation is as follows: 

The law of Dulong and petit can be mathematically represented as:

[c times M = k ]

Where,

c = specific heat capacity

M = molar mass

k = constant

Dulong and Petit did not know about this constant k. They found that elements with higher atomic weights as given by Dalton and early atomists were smaller and when multiplied by the specific heat capacity, it came out to be a constant. In modern times, this constant came out to be equal to 3R, where R is the gas constant. The Dulong and petit law then became:

[c times M = 3R ]

 

For a mass m of the sample divided by its molar mass M, gives us the number of moles.

 

[C times (frac{M}{m}) = 3R ]

 

[ frac{C}{n} = 3R ]

 

Where, 

C = heat capacity of the element

M = molar mass

m = mass of the sample

n = number of moles

 

At very low temperatures, the quantum mechanical energy stored within solids manifests itself with a larger and larger effect. The law then fails for substances in the cryogenic region. 

 

The Law of Dulong and Petit Formula

The Dulong and petit law can be used to find the valency and the atomic mass of the elements. The formula given by Dulong and petit is as follows.

 

[c times M = k ]

 

Where,

c = specific heat capacity

M = molar mass

k = constant

 

To find the atomic mass and valency of any element in its solid-state using Dulong petit law equation is given by-

 

Steps Involved

1. Calculate the approximate atomic mass using the formula.

Approx. atomic mass x specific heat capacity = 6.4

2. Find the valency of the element using the equation.

Approx. atomic mass = Equivalent mass and valency

3. Obtain the nearest whole number for the calculated valency. This is the valency of the element.

4. Calculate the corrected atomic mass of the element using:

Corrected atomic mass = Equivalent mass x valency

 

Limitation of Dulong Petit Law – 

Every set of theories comes with its own challenges and limitations. Similarly, the Dulong Petit Law has the following limitations – 

• The law is applicable only to those elements which are in solid-state

• The law is not applicable to lighter elements having a high melting point. Thus applicable only to the heavier elements. 

• The law gives only an approximate atomic mass. Thus, no exact number is given. 

 

Numerical Problem 

The equivalent mass of metal with a specific heat capacity of 0.03 is 69.66. Calculate the valency of the metal and its atomic mass using the law of Dulong and petit formula.

 

Solution-  To find the atomic mass and valency of the metal using Dulong and petit method we will-

 

Approx. atomic mass x specific heat capacity = 6.4

 

Approx. atomic mass = [frac{6.4}{0.03} ]

 

Approx. atomic mass = 213.33

 

Now that we have obtained the approximate atomic mass, we can calculate the valency of the element using the Dulong law-

 

Approx. atomic mass = Equivalent mass and valency

 

[frac{213.33}{69.66} = valency ]

 

3.06 = valency

 

By correcting the valency to its nearest whole number we obtain the valency of the element – 3.

 

Corrected atomic mass = 69.66 x 3

 

Corrected atomic mass = 208.98

 

The valency of the metal is 3 and its atomic mass is 208.98u.

 

Conclusion

The Dulong and petit law gives us an appropriate approximation of specific heat capacity and atomic masses of solids. Certain relationships which Dulong and petit could not explain were later discovered such as the kinetic theory of gasses, which gave the value of the constant they defined as ‘k’. The Dulong petit law stands for metals in their solid-state at higher temperatures
.