Category: Physics Notes PPT

Invented by the British physician William Gilbert around 1600, the electroscope is one of the most important instruments used by scientists for the past many years to study electricity. For centuries, it has been defined as a device made up of conducting material and used for detecting and testing the presence of ionizing radiation or electric charge on a body. Electroscopes detect the charge by the test object’s movement due to the Coulomb electrostatic force on it, and the amount of charge on that object is directly proportional to voltage. In cases where the electric charge of the object is equivalent to its capacitance, electroscopes are regarded as crude voltmeters. 

Working of Electroscope

An electroscope often consists of a metal rod with a knob on the top and a pair of metal leaves connected at the bottom. This rod is inserted into a one-hole rubber stopper that is further fitted into a flask. The flask contains the rod’s lower part, which includes the metal leaves. In the case of the uncharged electroscope, i.e., when no charge is present, the metal leaves hang straight down. However, when a charged object is brought near the knob of the rod, or we can say the electroscope, the electric charge travels down through the rod and spreads the leaves apart. This spreading of leaves indicates the presence of an electric charge. Note that when a charged object touches the knob of the electroscope, any of the following cases can occur:

• If the charge is positive, electrons in the electroscope are attracted to the charge and move out of the leaves in the upward direction. It makes the leaves gain a temporary positive charge, and as like charges repel each other, the leaves separate. 

• If the charge is negative, then the electrons in the electroscope repel and move towards the leaves. It makes the leaves gain the temporary negative charge, and as like charges repel, the leaves once again separate. 

In both the above cases, the electrons will return to their original position, and the leaves will relax as soon as the charge is removed. 

From all these statistics, we can conclude that the working of an electroscope is based on charge induction, the atomic and internal structure of the metal elements, and the notion that unlike charges attract while charges repel each other. Moreover, the electroscope cannot identify whether the charge is positive or negative; rather, it only determines the presence of the charge. 

Types of Electroscopes

In general, the electroscopes are classified into the following three types:

Pith-ball Electroscope: 

As the name suggests, it consists of one or two small balls that are made up of a lightweight non-conductive substance and known as pith. To determine whether the object is charged or not by using this electroscope, the object is brought close to the uncharged pith-ball. The force of attraction between the ball and object shows that the object is charged.

() 

Working

The pith-ball electroscope is used to detect static electric charges and to determine the polarity of unknown charges. As shown in the figure, the pith-ball A is made up of molecules consisting of positive and negative charges close together. Here, bringing a charged object B close to the pith-ball A makes the charges inside it separate slightly. Note that if the object is positively charged (as shown in the diagram), then the electrons, i.e., negative charges in the molecules will be attracted to it. They will move to the side of molecules close to the object. On the other hand, the positive charges, i.e., nuclei will be repelled, and move to the side of molecules away from the object. 

As the electrons are comparatively closer to the external charges than the nuclei, the force of attraction due to them is stronger than the force of repulsion due to nuclei. Though the separation of charges is microscopic, the total force (due to a large number of atoms in the pith-ball) is enough to pull the pith-ball towards the external charge. In this way, the pith-ball electroscope is used to detect the presence of a static charge on an object as if the object (when brought near to the ball) gets attracted to it. Moreover, by getting attracted to the object with the opposite charge and repelled by one with the same charge, the pith-ball can help you to determine the polarity of the charge on an object.  

Gold-leaf Electroscope: 

It consists of a vertical conductive rod with a metal ball on the top and two thin and parallel strips of gold leaf attached at the bottom. Invented by Abraham Bennet in 1787, this electroscope is comparatively more sensitive than a pith-ball one. To prevent the gold leaf from drafts of air, it is kept in a glass bottle. The gold leaves, which are kept in a glass flask to prevent them from the effect of air, spread apart into inverted “V” whenever a charged object is brought close to them.

()

 

Working

A gold-leaf electroscope is used for detecting electric charge present in a body and identifying its polarity. Its operation is based on the principle of electrostatic induction and like charge repulsion. In this electroscope, two thin leaves and an electrically conductive material are hung adjacent and virtually in contact with each other. Since the leaves are very thin, they possess no rigidity and hang down limply. When these leaves gain charge, they get separated. The angle that forms amid them depends on the amount of charge on them. If the instrument is shielded and the capacitance is fixed, then the angle may be with some precision to static voltage. Note that this electroscope indicates potential, not charge, and also that the voltage is determined by measuring the separation angle.  

Needle Electroscope:

It consists of a plate connected to a support stand and a pivoted free-swinging needle on either side of the stand. If a charged object is brought near to the plate, then the needle will gain the same charge and will swivel away.

() 

Working

In this electroscope, the plate, support stand, and needle are all made of a conducting material that allows both the free flow of electrons and the distribution of excess charge throughout the electroscope. Here, the presence of charge in not just the electroscope but also the nearby object can be determined by observing the deflection of the needle. The working of this electroscope often emphasizes the induction process of charging. In this process, the presence of the charged object that’s brought near to the plate of the electroscope influences electrons within the electroscope to move accordingly. With the charged object held close to the plate to which the electroscope is touched, the electrons will start flowing between the electroscope and the ground, providing the electroscope with an overall charge. Now, if the charged object is pulled away, the needle deflects, thus indicating the overall charge on the electroscope. 

Uses of Electroscope

An electroscope can be used to: 

• Detect the presence of ionizing radiation or electric charge on a body.

• Identify and compare the magnitude of charges.

• Calculate the force between two charges. 

• Detect the nature and relative amount of charges.

The energy state is also familiarly known as the energy level plays a vital role in explaining the atomic structure. The energy levels or the energy state is any discrete (definite) value from a set of values of total energy for a subatomic particle confined by a force to limited space or for a system of such particles, for example like an atom or a nucleus. The energy level is an old name used with the electron orbits of the Bohr model before quantum mechanics. In the quantum mechanical treatment and because of the uncertainty principle, thus we can not have orbits and hence the term energy states are used instead, thus technically there is not much of a difference between energy levels and energy states.

According to the photoelectric effect, we know that any electron striking on a metal surface can absorb the energy of one photon. In other words, an electron can absorb energy equal to h𝜈. An atom consists of a nucleus and free electrons revolving around the nucleus in discrete orbits. These valence electrons transition will cause different energy levels depending on the amount of energy being absorbed. In this article, we will have a deep insight into what is an energy state, energy levels, and its importance in understanding the atomic structures.

Energy Level

Let us have a look at the energy level with a simple illustration. Consider a positively charged nucleus such that an electron is revolving around it in its outermost orbital or shell. A photon is striking the electron and as a matter of fact, the electron will absorb the photon. As a result of the absorption of a photon by an electron one of the two things will occur:

1. If the electron acquires more energy after absorption of a photon, then the electron will get excited and thus it will jump to a shell that is further away from the nucleus. That implies the electron is gone up by an energy level and this process is known as the excitation.

2. If the electron was priorly having sufficient amount of energy to jump from present shell to another and as a result of absorption of photon electron will get furthermore energised in such a way that it will get away from shell or it gets removed from the energy level. This process is known as Ionisation. Basically, ionisation is a process in which when an electron is supplied with enough energy in such a way that it completely gets away from the atom and hence an ion will be created. The removal electron is known as ionization.

But the excited electrons will not stay in the excited energy level for a longer time, eventually, they will try to get back to their original state by de-excitation process. The electrons will lose their energy and transit back to the original state. Every transited level will be having a fixed value and these levels are generally known as the energy levels or the energy states.

What is an Energy Level?

Now, the question that arose is what is an energy level? Let us have a look at the actual meaning of the energy states and what is an energy level is. So, consider an atom with a nucleus and an electron is revolving around the nucleus in the specific shell or it can be anywhere above the considered shell depending upon the energy carried out by the electron itself and these energy levels are very particular for every atom. If we have a closer look at the shell where the electron is located and the levels above it, we observe a set of horizontal lines with definition spacing between them.

Energy levels (also called electron shells) are fixed distances from the nucleus of an atom where electrons can be located. Electrons are considerably small negatively charged particles in an atom that move around the positive nucleus at the centre. Energy level or the energy states are a little like the increments or steps of a staircase. You can stand on one particular step or another but can not stand in between the steps. The same goes for electrons. They can occupy only one energy level or another but not the space between energy levels.

A specific energy level corresponds to a specific value of n, in other words, all the energy levels are quantised in nature. For different integral values of n, we get different discrete energy levels. On the other hand, each discrete set of the four quantum numbers, i.e. {n, l, m_l, m_S}, designates each energy state. Let’s have a simple example to make these concepts more clear. Now, for n=2 energy level, we get eight distinct energy levels. But all these eight energy states or energy levels have the same value of the total energy because the total energy, as already stated, depends only on the principal quantum number n. Such types of distinct energy states having identical total energy are known as degenerate states and it is said that the energy level n = 2 is 8-fold degenerate. Similarly, we can prove that n = 3 energy level is 18-fold degenerate.

 

Thus, Energy states (also known as the electron shells) are just fixed distances from the nucleus of an atom where the electron density is more. As we move farther away from the nucleus, electrons at higher energy (excited states) levels have more energy. Electrons are always added to the most possible lowest energy level first until it has the maximum number of possible electrons, and then electrons are added to the immediate next higher energy level until that level is full, and the process goes on. The maximum number of electrons at a given energy state depends on its number of orbitals. There are at most two electrons per orbital. Electrons in the outermost energy state of an atom are called valence electrons. They are helpful in determining many of the properties of an atom, including how reactive it is.

Did You Know?

One of the important concepts regarding energy levels is that with classical potentials, the potential energy is usually set to zero at infinity, leading to negative potential energy for bound electron states. This is found to be helpful in determining the many intrinsic properties of an atom.

Have you ever wondered how rockets take off? While going off to space, rockets need a push, some sort of force that lets them leave the earth and go into space. This is a huge kickstart that they have to be given, otherwise the result, that is them leaving the earth’s surface, would not happen. 

But, what is the reason behind the need for such a huge kickstart? Well, it all comes down to the gravitational field that is there on the surface of the earth. In case you didn’t know, it is a very strong force for which an all the more strong “push” is required for the rockets to send them into space. 

Escape Velocity is the minimum Velocity that is required for a body or an object to leave or “Escape” the gravitational field of the surface of the earth. Furthermore, it is always the goal for Escape Velocity to have an object leave the face of the earth without a chance for it to ever fall back due to the gravitational pull of our planet.

Orbital Velocity

Do you know what happens if an aeroplane stops? Well, on such an occasion, it will be pulled towards the earth’s surface due to the force of gravity. There are satellites, amongst other objects in the space sent by us, which require the velocity that can withstand as well as defy the gravitational pull of our planet. 

Any object requires to sustain a certain speed that can easily let them have a good alignment with the celestial body’s rotational velocity. The speed is also important to be enough to sustain the kind of gravitational pull that comes from the earth. 

Definition of Orbital Velocity

When an object needs to enter into an orbit of any other celestial bodies, it is a must that they obtain a speed that can help them counteract the gravitational force.  

The lowest velocity an object must have to escape the gravitational force of a planet or an object. The relationship between the Escape Velocity and the Orbital Velocity is defined by V_e = 2 Vo where Ve is the Escape Velocity and Vo is the Orbital Velocity. And the Escape Velocity is root-two times the Orbit Velocity.

Escape Velocity, as it relates to rocket Science and space travel, is the Velocity required for an object (such as a rocket) to Escape the gravitational Orbit of a celestial body (such as a planet or a star).

We have studied in kinematics that the range of the projectile depends on the initial Velocity of the projectile. ⇒ R_max ∝ u₂ ⇒ R_max = [frac {u_2}{2g}], which means that the particle flies away from the gravitational impact of the earth at a certain initial Velocity provided to the particle. 

This minimum amount of Velocity for which the particle Escapes the gravitational sphere of influence of the planet is known as the Velocity of Escape (ve). When an Escape Velocity is given to a body, it theoretically goes to infinity.

As gravitational force is a conservative force, the law on energy conservation is fine. Applying the law on the conservation of energy for a particle with the necessary minimum Velocity to infinity

U_i + K_i  = U_f + K_f

At infinity, the particles undergo no interaction, so the final potential energy, and we know from motion in the 1D chapter that the final Velocity of the body is zero after reaching its maximum height so that we can deduce the final kinetic energy of the particle.

Then ,

Ui + Ki  = 0 and   we   know   that, Ui ​= [frac {-GMm}{R}] , Ki​= [frac {1}{2mv_{e}^2}]  

We get,  

[frac {1}{2mv_{e}^2}] + [(frac {-GMm}{R})] = 0 ⇒ [frac {1}{2mv_{e}^2}] = [(frac {GMm}{R})]

That implies,

v_e​= [sqrt {frac {2GM}{R}}] ​​ ……………(1)  

It is obvious from the above formula that the Escape Velocity does not depend on the test mass (m). If the source mass is earth, the Escape Velocity has a value of 11.2 km / s. When v = ve the body leaves the gravitational field or control of the planets, when 0 ≤v < ve the body either falls down to Earth or proceeds to Orbit the earth within the sphere of influence of the earth.

Orbital Velocity is the Velocity that the body will sustain in order to Orbit another body. Escape Velocity is the speed at which an object leaves the Orbit. Escape Velocity will be a square-root of 2 times the Orbital Velocity in order to exit the Orbit.

(l) If the Velocity is equal, the body must remain in constant Orbit, not in elevation.

(ll) less than the Orbit, the Orbit will decay and the object will crash.

(ll) rather than Orbital, and the body will have an ascending Orbit, which will fly out into space.

The speed at which the test mass travels around the source mass is known as Orbital Velocity

(v_o) when the test mass Orbits around the source mass in a circular path of radius ‘r’ having the center of the source mass as the center of the circular path, the centripetal force is provided by the gravitational force as it is always the attracting force having its direction towards the center of a source mass.

⇒ [frac {mv_o^2}{r}] = [frac {GMm}{r^2}]

⇒ [frac {v_o^2}{r}] = [frac {GM}{r^2}]

 

⇒ v_o ​= [sqrt {frac {GM}{R}}] 

If the test mass is small distances from the source mass  r ≈ R (radius of the source mass)

Then,

v_o​ = [sqrt {frac {GM}{R}}] …………..(2)

The above formula indicates that the Orbital Velocity is independent of the test mass (the mass which is Orbiting).

Relation Escape Velocity And Orbital Velocity Formula

In astrophysics, the relationship between Escape Velocity and Orbit Velocity can be mathematically described as –

V_o=[frac {V_e}{sqrt{2}}]

Or

V_e= [sqrt{2}V_o]

Where,

We know that Escape Velocity= [sqrt {2} times ] Orbital Velocity that means that the Escape Velocity is directly proportional to the Orbital Velocity. This means for any big body-

• When the angular Velocity increases, the Escape Velocity will also increase and aim-versely.

• If the angular Velocity decreases, the Escape Velocity decreases as well as the vise-versa.
  

Escape Velocity and Orbital Velocity

The relationship between Escape Velocity and Orbital Velocity equations is very important for understanding the definition. For any kind of massive body or planet.

Where,

g is the acceleration due to gravity.

R is the radius of the planet.

From equation (1) we can write that-

V_e= [sqrt {2}]  [sqrt {gR}]

Substituting Vo = [sqrt {gR}] we get-

V_e=[sqrt {2} V_o]

The above equation can be rearranged for Orbital Velocity as-

V_o = [frac {V_e}{sqrt{2}}]

The branch of physics that deals with the study of the electromagnetic force, which involves the interaction between the electrically charged particles are known as electromagnetism. Let us see who discovered electromagnetism? Electromagnetism was first discovered by William sturgeon. Electromagnetic induction or magnetic induction is the process through which the electromotive force is produced across an electric conductor in a changing magnetic field. Let us know ‘who discovered electromagnetic induction?’. It was discovered by Micheal Faraday in 1831 and it was mathematically described as Faraday’s law of induction by James Maxwell. The direction of this induced field was described by Lenz’s law. 

Faraday Experiment

Now we know who discovered electromagnetic induction, let us see how he invented it. Faraday demonstrated his experiment using an iron ring or torus, to which he wrapped the iron wires on the opposite sides. Depending on the understanding of the electromagnets he thought that when the current flows through a wire a kind of wave will start travelling through the ring, on the opposite side this wave will cause an electrical effect. He connected one end of the one wire to the galvanometer and the other end to the other wire to the battery, now he watched the fluctuations of the needle in the galvanometer. There he found a transient current and called it a Wave of electricity. This electricity was found when the wire is connected to the battery and then disconnected. 

In Faraday’s discovery of electric induction, due to the change in magnetic flux, this induction of electricity has occurred when the wire is connected to the battery and then disconnected. And with the span of two months, he observed several manifestations that are related to electromagnetic induction. One of them is as he saw the transient current when the bar magnet was slid in and out of the coil. By rotating the copper disk near the bar magnet with the help o a sliding electrical lead he generated a steady current also known as DC current. 

Faraday electromagnetic theory was explained by using a concept which he called lines of force. As they were not formulated mathematically scientists who are present at that time rejected his theoretical work. But except a scientist called James Maxwell used Faraday’s ideas as the basis of his electromagnetic theory. The time-varying aspect is expressed as the differential equation of the electromagnetic induction, this was referred to as Faraday’s law by Oliver Heaviside even though it was different from that of the original Faraday’s formulation and it has not described the motional EMF. 

Faraday’s Laws

In the Faraday experiment, we have found how electric induction has occurred, now let us go through the laws he discovered. 

Faraday’s law of induction and Lenz’s law: Faraday’s law of induction uses magnetic flux through a region of space that is being enclosed by a wire loop. The magnetic flux used is defined by the surface area, Ф = [int_{Σ}] B. dA 

In the equation given above “dA” indicates that the element of the surface Σ that can be enclosed by a wire loop. Whereas B indicates the magnetic field. The dot product of the magnetic field and the surface of the element indicates the infinitesimal amount of the magnetic flux produced. It can also be said that the magnetic flux through the wire loop is proportional to the number of magnetic flux lines that are passing through the loop. 

Faraday’s law says that when the flux through the surface changes the wire loop acquires the EMF (Electromotive force). In a detailed way, we can tell that the EMF induced in the closed circuit is equal to the magnetic flux that is enclosed in the circuit. 

ε = – [frac{dФ_{B}}{dt}]

From the above equation, we can tell that is the EMF induced, Ф_B is the magnetic flux. Thus the direction of this EMF is given by Lenz’s law. It states that “The direction of flow of an induced current opposes the change that is produced by it”. Thus a negative sign is added to the equation. The generated EMF can be increased by exploiting the flux linkage by creating a tightly wound coil, this coil has N identical turns through which the same magnetic flux passes through it. Thus the resulting EMF is N times as that of the turns. 

ε = – N [frac{dФ_{B}}{dt}]

Electromagnetic Force Discovery

In the world of physics Faraday and Maxwell, together, made great discoveries, the ones who discovered electromagnetic induction. Faraday with his experiments magnetic and electric fields are not telekinetic actions but they are the expression of physical things. With these experiments, Maxwell was inspired and he combined the ideas of all these results. The electromotive force produced across an electric conductor in a changing magnetic field is known as electromagnetic induction. The EMF is induced around the loop when the magnetic field through that wire varies.

Applications

The Principle of Electromagnetic Induction is Used in Many Systems and Devices:

1. Electric Generator: The relative motion of the magnetic field and the circuit led to the generation of electric induction, this was discovered by Faraday this phenomenon is related to the electrical generators. When a permanent magnet moves in relation to the conductor or in vice versa an EMF is produced. The current flows through the wire that is connected to the electrical load thus electrical energy is generated by converting the mechanical energy into electrical energy. 

The best example that suits this is the drum generator that is implemented using the idea of Faraday disc. 

Here the rotating disc that is placed in the field of the uniform magnetic field that is perpendicular to the disc produces current that flows through the radial arm that is obtained by Lorentz force. To drive this current, mechanical work is required; a magnetic field is generated when this current flows through the conducting rim by the Ampere’s circuital law. Now the rim acts as an electromagnet that opposes or resists the rotating motion of the disc. Through the far sides of the rim, the return current flows from the rotating arm to the brush present at the bottom level. Current opposes the applied magnetic field resulting in the decrease of the flux at that side of the circuit. This opposes the flux that is increasing due to the rotation. The energy that is required to allow the disc in the motion despite that of the reactive force is equal to the electrical energy generated in the circuit. Thus this conversion of mechanical energy into electrical energy is found in all types of generators.

2. Electrical Transformer: The electrical current that flows through the loop of wire changes creates the changing magnetic field. The second wire that is in contact with the wire where the magnetic field is created experiences the change in the magnetic field. This is experienced as a change in the coupled magn
   etic flux. Thus the electromotive force formed in the second wire EMF is called induced EMF or transformer EMF. The flow of current can be observed when the two ends of these wires are connected to the electrical load. The best example of this is the Current clamp, it is a type of transformer that has a split core that can be clipped onto a coil or wire or it can be spread apart, this is done to calculate the current flowing through it or the current flowing in the reverse direction to the induced voltage. As per the conventional instruments it is not required to disconnect the clamp or it doesn’t make any electrical contact with respect to the conductor.

3. Magnetic Flow Meter: Faraday’s law is used to determine the flow of electric current in the conductors and slurries. These types of instruments are called magnetic flow meters. The induced voltage is generated in the presence of a magnetic field due to the conductive moving liquid at the velocity is given by:

ε = – Blv

Where is B is a magnetic field, ε is the voltage induced, v is the velocity and l is the distance between the electrodes that are present in the magnetic flow meter.

Eddy Current

The electrical conductors that are moving through the steady magnetic field or the conductors that are stationary in nature are placed in changing magnetic fields; the circular currents induced in them are known as eddy currents. The eddy current flows through the closed loops in a plane that is perpendicular to that of the magnetic field. The eddy current is applied in the induction heating system and eddy current brakes. But the eddy currents that are induced in the metal magnetic cores of the AC motors and transformers are undesirable as they dissipate energy this is known as core losses. Thus to avoid core losses many methods are used: Instead of using the solid metal as the core, thus cores of low-frequency AC transformers and electromagnets. These are made of stacks of metal sheets known as laminations. The inductors and the conductors that are used for high frequency in these devices the magnetic core is made of non-conductive material that is magnetic in nature; they are iron powder or ferrite. 

• When the solid metallic mass is rotated the eddy currents occur in the magnetic field due to the reason that more number of the magnetic field of lines passes the outer portion of the metal than that of the inner portion. Thus the EMF induced is not uniform. 

• The eddy currents consume only a considerable amount of energy thus causing a rise in the temperature. 

Conclusion

The man who invented electromagnetic induction is Micheal Faraday. Where electromagnetic induction is the production of the EMF across a conductor that is conductive electrically in the presence of the magnetic field. The branch of physics which deals with the study of the EMF is known as electromagnetism. By the results that were produced in the Faraday, the experiment was used by Maxwell to invent more in the field of physics. This is the principle behind generators and electrical transformers that are being used today. These two devices play an important role in the production and regulation of electrical current.

When a current-carrying conductor is kept in a magnetic field, a force applies on it; the direction of this force can be determined using Fleming’s Left-Hand Rule. Similarly, if a moving conductor is placed in a magnetic field, an electric current will be induced in it. The direction of the induced current can be determined using Fleming’s Right-Hand Rule.

It’s vital to note that these rules don’t define magnitude; rather, they demonstrate the direction of the three parameters (magnetic field, current, and force) when the other two parameters’ directions are known. Electric motors are predominantly affected by Fleming’s Left-Hand Rule, while electric generators are primarily affected by Fleming’s Right-Hand Rule.

Fleming’s Left-hand Rule and Fleming’s Right-hand Rule

Fleming’s Left-hand Rule

Fleming’s left- hand rule states that if we stretch the thumb, middle finger and the

The index finger of the left hand in such a way that they make an angle of 90 degrees (Perpendicular to each other) and the conductor placed in the magnetic field experiences Magnetic force.

Then the direction for each finger is represented as follows:

()

Fleming’s Right – hand Rule

Fleming’s Right hand Rule states that if we stretch the thumb, middle finger, and an index finger in such a way that they are mutually perpendicular to each other.

 

Then the direction for each finger is represented as follows:

• Thumb: It is along the direction of motion of the conductor.

• Middle finger: It points in the direction of the induced current.

• Index finger:  It points in the direction of the magnetic field.

The representation for right-hand rule is as follows:

()

On this page, we shall learn the following things: 

• Fleming’s left- hand rule

• Fleming’s left- hand rule application

• Fleming’s right-hand rule

• Difference between Fleming’s left-hand and fleming’s right-hand rule

Fleming’s Left-hand Rule Application: Working of an Electric Motor

Theory behind Fleming’s left-hand rule: When current  flows through a conducting wire, and an external magnetic field is applied across that flow, the conducting wire experiences a force orthogonal both to that field and direction of the current flow, like we see in the image below:

()

Working of an Electric Motor 

Let’s take a rectangular current carrying loop and put it inside the magnetic field as shown below:

()

Here, in the above diagram of the electric motor, we notice that each side of the loop behaves as a current-carrying conductor.

Also, the direction of force is different at each side of this conductor, and that force is acting on that conductor due to the production of the magnetic field, these magnetic field lines would make varying forces at each side, and the direction of the force at each side of this loop can be determined by using Fleming’s left-hand rule, and electricity changes to the rotatory motion.

 

Now, look at the pink wire, and observe the direction of the current to determine the direction of the force and the magnetic field: 

()

     

Now, let us apply Fleming’s left-hand rule for the blue wire:

()

As soon we applied Fleming’s left-hand rule:

We can see the direction of the Force and magnetic field in Fig.3

In pink wire: The force is acting ‘upwards.’

In blue wire: The force is acting ‘downwards.’

But one thing we can see in orange wire, the current is flowing in the right direction while magnetic field B is in the left direction. The current and magnetic field is in the opposite direction.

The magnetic field B is parallel to the orange wire, hence no force would act upon it. How would the loop rotate?

Additionally, in an orange wire, the current is flowing in the right direction while magnetic field B is in the left direction. The flow of current and the magnetic field are in the opposite direction.

So, if the magnetic field B is parallel to the orange wire, no force would act upon it, so how will the loop rotate? It’s because forces acting in opposite directions make the loop rotate. Now, let us understand how.

()

In Fig.4, we can see that forces are in opposite directions and the loop starts rotating in a clockwise direction.

()

Here, in fig. 5, we notice that though forces are in opposite directions, their direction doesn’t change. Also the orange wire is not parallel, and it makes some angle with the magnetic field lines, which is why the loop rotates. 

The direction of force is not changed, the orange wire is not parallel, and making an angle with the magnetic field lines, and now applying fleming’s left-hand rule here: we get like this:

()

Force in the lower orange wire is outwards, and that of the upper orange wire inward wire inwards.

The orange wires would try to distort the loop, as the loop is of very high strength and the spinning of the loop won’t be there at this moment. Here, we would consider these two forces as negligible.

Now, as the loop rotates again in the following manner (Fig. 7), the problem arises that again the forces are in opposite directions, first, it will slow then it would start rotating in an anticlockwise direction: like this:

()

As soon as the rotation starts, the wire will get distorted like this:               

Now, in place of changing the direction of the magnetic field, we change the direction of current by attaching a battery with the wire and we notice that as the rotation starts, the wire will distorts in the following manner:

()

However, the above process would continue and won’t allow a complete rotation in one direction.

To resolve this issue, we use the commutator and a carbon brush for a complete rotation of the loop to avoid distortion in the wire, as we can see in Fig. 8 above.

Now what we can do is use the commutator and a carbon brush for a complete rotation of the loop without getting the wire distorted.

Here,  Commutator is a split ring with two metallic halves.

Carbon brushes are just touching the Commutator and are linked with wire, so that if the current reaches the loop via these brushes. 

A commutator is a split ring with two metallic halves. Carbon brushes are just touching the Commutator and are linked with wire, so that if the current reaches the loop via 

these brushes.    

After we have connected the communicator to the arrangement, we notice that after a half ro
tation, the position of the split ring position changes in the following manner (Fig. 9), the terminals of the battery connected across the split rings are also changing and helps change the direction of the current in the following figure. 9:

Now after a half rotation, the position of split ring position changes like this:

()

As we can see the terminals of the battery connected across the split rings are also changing and would help in changing the direction of the current as well.

This is how an electric motor would make a complete rotation.

So this is how fleming’s left-hand rule is applied to an electric moto

Hence, our issue was resolved by using a commutator for the smooth rotation of the motor.

So, we learnt that we use Fleming’s left-hand rule for the smooth functioning of electric motors. This reason makes this rule a renowned application of electric devices.

 

Solved Example on Magnetic Field in a Current-Carrying Conductor

Let’s take a conductor placed in a magnetic field:

()

Here, K L being the length of the current-carrying conductor (rod),  F is the force and the B be the magnetic field, then:

F = I * B * K L

B = F / I * K L

Unit of B = N/ A * m.

S.I. unit of I is A

S.I unit of k L is m.

and for B, it is Tesla.

1 Tesla = 1 N / Am

Concept Bases Questions:

1. Let’s say the current flowing the conductor is 5 A, length of the rod be 4m and the magnetic field generated by 3 T. Find the force produced.

Solution: 

Given:  I = 5A, L = 4m, and B = 3 T

Since, F = I * B * L

              = 5 * 3 * 4

           F = 60 N

Thus, the force produced is 60 N.

2. An electric current is moving from right to left in the wire. Which way does the induced magnetic field point to the location of the triangle?

()

Solution: 

Applying Fleming’s left-hand rule: Rotating your middle finger in the direction of an electric current that is in the right direction, we get that the force is pointing inwards and the direction of the magnetic field is downwards that is into the screen.

3. A current-carrying conductor does not tend to rotate in a magnetic field. Why does this happen?

It means, no force is acting on the current-carrying conductor due to the magnetic field, which means that the current-carrying wire is parallel to the magnetic field.                        

4. Is the source of the magnetic field analogous to the source of electric current?                  

No, it’s because the source of the magnetic field is not a magnetic charge. However, in the case of the electric field, the source of the electric field is an electric charge.

What is Force?  How Does Force Interaction Work? 

Before we say into how force can influence the condition of movement of a body, how about we take a look at the force. So, basically how you define or explain the terminology ‘force?’ Force is an association between at least two bodies that when unopposed causes an adjustment in the condition of movement of the objects. So in the meaning of force itself, it explicitly expresses that force is something that causes an adjustment in the condition of movement. 

Force interaction can likewise be thought of as a push or a pull. An adjustment in the condition of movement relates to either an adjustment in the speed of the body as well as an adjustment toward the movement of the body. The adjustment in speed could mean an accelerating (increasing speed) or speed down (deceleration). The movement in the ball can’t happen on its own, neither can a stool or a table. All non-living items are fixed except if power is following upon them. 

You have to apply energy to create a force to make it move, you have to kick the ball which is a type of applied force altogether for the ball to fly into the objective. At times various forces can follow up on a similar body. Envision that you are kicking a ball and your companion has precisely the same thought. What might occur if you both kicked the ball all the while? Have a look at what we discover from the following explanation along with the examples.  

(Image to be added soon)

The force that changes shape

Forces Interaction

Have you played with your companions the game of tug-of-war? What occurs in a tug-of-war is that two groups pull a solitary rope. The group that can pull the rope by a specific amount despite the other group pulling it wins. So what precisely is going on here? Two forces in a tug-of-war game are acting in reverse directions. 

One group is pulling the rope towards the right and another is attempting to pull the rope to the other side similarly as hard. This makes the two forces counterbalance each other similarly as – 3 and +3 counteract one another. That is one situation dealt with. What occurs if forces are acting similarly? Is it simpler to push a vehicle without anyone else or with the assistance of two or three of your companions? It is easier than you push the vehicle together right? This is because force includes as well. 

At the point when you and your companions are pushing in a similar direction, every one of your forces are following up on the vehicle subsequently making it easier to push it together. To sum up, if forces are acting in inverse directions they counteract one another and if they are acting in a similar direction, they add up. 

The Impact of Force on the Object’s Shape 

Have you at any point played with clay? It is an incredibly irregular material. At the point, when you press a clay ball, it doesn’t move. It loses its shape. You must have seen your mom mixing the flour into the dough to make chapattis. Have you ever felt the mixture of dough? At the point when you press the dough, it changes its shape with the force applied. It does it so well if you notice intently, even your fingerprints are squeezed into the batter. 

This is a property of the material. This is something different from other materials, for example, elastic rubber bands and springs. Materials, for example, change their shape on the use of force however when the force is expelled the material returns back to its unique position. The materials which change their shapes for all time on the utilization of force, for example, clay and dough are called Plastic materials. 

This isn’t to be mistaken for actual plastic. Materials that experience shape change on the utilization of force however recaptures their unique shape on the evacuation of force are called Elastic materials.