Positive And Negative Torques
Torques that occur in a counter clockwise direction are positive torques. Alternatively, torques that occur in theclockwise direction are negative torques. So what happens if your hand points in or out of the paper? Torques thatface out from the paper should be analyzed as positive torques, while torques that face inwards should be analyzedas negative torques.
Force On A Current In A Magnetic Field
The strength of a magnetic field is usually measured in terms of a quantity called the magnetic flux density of the field, B. A definition of B requires a consideration of the forces produced by electromagnetic fields.When a wire carrying a current is placed in a magnetic field the wire experiences a force due to the interaction between the field and the moving charges in the wire. A very good demonstration is the so-called catapult field experiment in which a wire carrying a d.c. current can be made to move in the field of two flat magnets. .
The force F on the wire in Figure 4 can be shown to be proportional to the current on the wire I, the length of the conductor in the field L, the sine of the angle that the conductor makes with the field , and the strength of the field – this is measured by a quantity known as the magnetic flux density B of the field. The force is given by the equation:
B Electrons Quantum Mechanics
Now consider the same experiment on a much smaller scale. Instead of bullets from a machine gun we consider electrons that for example can stem from a heated wire parallel to the two slits in an intermediate wall. The electron direction will have a natural spread. The slits are also much smaller than before but much broader than a single electron.
The electron experiment results
Consider again the case that the second slit is blocked. For proper sizes of the slits and distance between the wire and the walls, the probability distribution P1 will be similar to before. Similarly, if we block the slit 1, we will for proper distances find a probability distribution P2 similar to before.
What do you expect will happen if we do not block any slit? Will we find a probability distribution P = P1 + P2 as before? Well, after all we said you may guess that this is not the case. Indeed, we will instead find a probability distribution that has various minima and maxima. That is, for x = 0 there would be the strongest peak of electrons, for a certain +-Delta x there wouldnt be any electrons at all, but for +-2 Delta x there would be another peak of electrons, and so on.
Explanation of the electron experiment results
So, why do electrons in this case behave like waves and not like particles? Well, this is the thing where you will not find a satisfying answer. You just need to accept it.
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Maxwells Equation In Qed The Same But Better
I wouldnt get into the details, but within the language of Quantum Field Theory , all four of Maxwells equations in a vacuum can be written in one single but extremely compact form.
where electromagnetic tensor F is a 4-vector that combines the electric field E and the magnetic induction B
and the charge and current density are also combined to one current 4-vector
If you are interested in reading more about the beauty and the challenges of the powerful techniques of quantum field theories, I recommend the article below.
Parallel Current Carrying Conductors
Where F = Force Newtons N
l = Length of the current carrying conductors parallel to each other.
k = constant mu0/2p = 2 x 10-7 SI Units
I1 and I2 are current carrying conductors respectively
d = distance between the current carrying conductors
Radius is large for more massive, faster particles.Radius is smaller when the magnetic field strength is large
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Symbols Used In Modern Physics
From the above text on physics symbols, we understand that in Physics, we use various symbols or notations to denote different quantities. The denotations make the representation of the quantities easier.
It was also interesting to see that some physics symbols were very relatable while some were unrelatable . Also, we noticed that a particular symbol was related to more than one quantity.
Magnets North And South Poles
Imagine we are given a set of magnetics, and we begin playing with them to explore magnetic phenomena. One of the first things we find is that we can get a pair of magnets to stick when some ends face each other, but turning one of the magnets around causes the magnets to start repelling. We find that bar magnets can attract or repel other magnets depending on which ends are brought together. We need a way to label the two ends.
The convention is that these two distinct ends of a magnet are called the north pole and the south pole. This convention is related to the use of magnets in navigation. The development of the navigational compass makes use of the interaction between bar magnets and the Earth . The poles are defined thus: If we suspend any magnet freely on a table the end of the magnet that points towards the north geographic pole of the Earth is referred to as the north-seeking pole or just the north pole. The opposite end is the south-seeking pole or just the south pole.
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Definitions Of B And H
The concept of magnetic field is fundamental in physics, but it is difficult to define – in the same sense it is it difficult to define what is time. Therefore, the definitions of magnetic field, magnetic field strength $H$ and magnetic flux density $B$ are usually somewhat convoluted or even circular, as shown in some examples from important literature, as cited below.
Maxwell Thought The Existence Of Aether Or Medium Is Necessary
Its interesting that Maxwell discusses the necessity of the aether to exist throughout the book and criticizes everyone else who thinks differently.
In support of his opinion, he also included the letter from Gauss to Weber from 1845.
In a very interesting letter from Gauss to W. Weber, he refers to the electrodynamics speculations with which he had been occupied long before, and which he would have published if he could then have established that which he considered the real keystone of electrodynamics, namely, the deduction of the force acting between electric particles in motion from the consideration of an action beteween them, not instantaneous, but propagated in time, in a similar manner to that of light. He had not succeeded in making this deduction when he gave up his electrodynamic researches, and he had a subjective conviction that it would be necessary in the first place to form a consistent representation of the manner in which the propagation takes place.
He finished the treatise, concluding the aether has to exist.
Hence all these theories lead to the conception of a medium in which the propagation takes place, and if we admit this medium as an hypothesis, I think it ought to occupy a prominent place in our investigations, and that we ought to endeavour to construct a mental representation of all the details of its action, and this has been my constant aim in this treatise.
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What Is The Importance Of Physics Symbols
In physics, there are a large number of physical quantities we include while performing calculations. To make it more convenient for users and easier to use and remember, we often use notations/symbols to represent these physical quantities. These notations/symbols we use to represent physical quantities when solving problems related to them or for other purposes are symbols.
In physics, we symbolise everything with an English/Greek alphabet, such as for the speed of light, wavelength, velocity, and so on.
Let us assume that a lady drives her car at a speed of 30 kmph and reaches her hometown in 2 hrs and if she drives at 50 kmph, she reaches in 1.5 hr. So, if we have to represent these units as symbols, how can we do that?
In this article, you will find the most popular physics symbols and also those we commonly use in physics with their names, the type of quantities along with their respective units in tabular format.
Watch The Video To Find Out What Base Measurements Are
Keep visiting BYJUS to get more such information. BYJUS also helps the students for their exams by providing sample papers, question papers and preparation tips.
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Right Hand Rule For Torque
Torque problems are often the most challenging topic for first year physics students. Luckily, there’s a right hand ruleapplication for torque as well. To use the right hand rule in torque problems, take your right hand and point it in thedirection of the position vector , then turn your fingers in the direction of the force and your thumb will pointtoward the direction of the torque.
The equation for calculating the magnitude of a torque vector for a torque produced by a given force is:
When the angle between the force vector and the moment arm is a right angle, the sine term becomes 1 and the equationbecomes:
F = force r = distance from center to line of action
Quantum Physics Introduction For Beginners
In this quantum physics introduction for beginners, we will explain quantum physics, also called quantum mechanics, in simple terms. Quantum physics is possibly the most fascinating part of physics that exists. It is the amazing physics that becomes relevant for small particles, where the so-called classical physics is no longer valid. Where classical mechanics describes the movement of sufficiently big particles, and everything is deterministic, we can only determine probabilities for the movement of very small particles, and we call the corresponding theory quantum mechanics.
You may have heard Einsteins saying, Der Alte würfelt nicht which roughly means God does not roll dice. Well, even geniuses can be wrong. Again, quantum mechanics is not deterministic, but we can in general only determine probabilities. Since we are used to reasonably big objects in our everyday life, quantum mechanics and its laws may initially seem strange and quantum theory is often considered complex. But for example, electrons and photons are sufficiently small that quantum physics is needed, and on this website, we will show you that understanding the basics of quantum physics is easy and fun.
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Magnetic Field Due To Moving Charges And Electric Currents
All moving charged particles produce magnetic fields. Moving point charges, such as electrons, produce complicated but well known magnetic fields that depend on the charge, velocity, and acceleration of the particles.
Magnetic field lines form in concentric circles around a cylindrical current-carrying conductor, such as a length of wire. The direction of such a magnetic field can be determined by using the “right-hand grip rule” . The strength of the magnetic field decreases with distance from the wire.
Bending a current-carrying wire into a loop concentrates the magnetic field inside the loop while weakening it outside. Bending a wire into multiple closely spaced loops to form a coil or “solenoid” enhances this effect. A device so formed around an iron core may act as an electromagnet, generating a strong, well-controlled magnetic field. An infinitely long cylindrical electromagnet has a uniform magnetic field inside, and no magnetic field outside. A finite length electromagnet produces a magnetic field that looks similar to that produced by a uniform permanent magnet, with its strength and polarity determined by the current flowing through the coil.
The magnetic field generated by a steady current I is described by the BiotâSavart law::224
Symbols For Physical Quantities Related To Space And Time
Radius, the radius of curvature
Functions as both scalar and vector
A uniquely-defined magnitude and direction, but is not a vector quantity.
x, y, z
Functions as both scalar and vector
Below are some symbols that are used frequently in physics with their names, the type of quantities and their respective SI units in tabular format.
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Examples Of Physical Symbols
Also, the symbols used for physical quantities are vastly different. Sometimes, the symbol may be the first letter of the physical quantities they represent, like d, which stands for distance. Other times, they may be completely unrelated to the name of the physical quantities, such as c symbolises the speed of light. They may also be in the form of Greek characters, like , which stands for wavelength.
Below is an elaborated list of the most commonly used list of symbols in physics with their SI units. Please note that a particular symbol might relate to more than one quantity.
Magnetic Force On A Moving Charge
F = BqV
F is the force being undergone by the charge – measured in Newtons
B is the magnetic field strength of the field the charge is in – measured in Teslas
q is the charge of the charge – measured in Coulombs .
v is the velocity of the charge – measured in meters per second
The direction of the Force may be determined using the Right-hand rule.
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Ampre’s Law And Maxwell’s Correction
Similar to the way that a changing magnetic field generates an electric field, a changing electric field generates a magnetic field. This fact is known as Maxwell’s correction to AmpÃ¨re’s law and is applied as an additive term to Ampere’s law as given above. This additional term is proportional to the time rate of change of the electric flux and is similar to Faraday’s law above but with a different and positive constant out front.
The full law including the correction term is known as the MaxwellâAmpÃ¨re equation. It is not commonly given in integral form because the effect is so small that it can typically be ignored in most cases where the integral form is used.
The Maxwell term is critically important in the creation and propagation of electromagnetic waves. Maxwell’s correction to AmpÃ¨re’s Law together with Faraday’s law of induction describes how mutually changing electric and magnetic fields interact to sustain each other and thus to form electromagnetic waves, such as light: a changing electric field generates a changing magnetic field, which generates a changing electric field again. These, though, are usually described using the differential form of this equation given below.
Solved Example On Magnetic Field Strength
Q1 Calculate the magnetic field strength inside a solenoid which is 2 m long and has 2000 loops. Furthermore, it carries a 1600 A current?
A1 In order to find the magnetic field strength inside the solenoid, one must use B = \. Furthermore, one must note the number of loops per unit length:
n = \ = \ = 1000m-1 = 10 cm-1.
Now, one must substitute known values
B = \ = \\left \left \)= 2.01 T.
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I Checked Maxwells Textbook From 1873
In 1873 Maxwell finished A treatise on Electricity and Magnetism. Among various phenomena and problems discussed, his 900-pages book includes a compact and elegant way of writing the fundamental interrelationship between the electrical and magnetical quantities that he gradually formulated over the years. A set of electromagnetic laws we today know as Maxwells equations are in their mathematical beauty able to enclose the entire classical electromagnetism in a few lines of equations.
The formulation of these equations is the most important event in physics since Newtons time.
From a long view of the history of mankind seen from, say, ten thousand years from now there can be little doubt that the most significant event of the 19th century will be judged as Maxwells discovery of the laws of electrodynamics.
In modern notation, where the magnetic field is denoted with H and magnetic induction with B, Maxwells equations of classical electromagnetism are written as a set of four equations. In their differential form, they are:
- The third Maxwell equation, also known as Faradays law,is the basic principle of how electric generators work. A time-varying magnetic induction generates a curling electric field .
- Finally, Amperes law relates the curl of magnetic field with the free current and the displacement current . This is the basic principle of how electric motors work.
Magnetic Torque On Permanent Magnets
If two like poles of two separate magnets are brought near each other, and one of the magnets is allowed to turn, it promptly rotates to align itself with the first. In this example, the magnetic field of the stationary magnet creates a magnetic torque on the magnet that is free to rotate. This magnetic torque Ï tends to align a magnet’s poles with the magnetic field lines. A compass, therefore, turns to align itself with Earth’s magnetic field.
In terms of the pole model, two equal and opposite magnetic charges experiencing the same H also experience equal and opposite forces. Since these equal and opposite forces are in different locations, this produces a torque proportional to the distance between them. With the definition of m as the pole strength times the distance between the poles, this leads to Ï = Î¼0m H sinÎ¸, where Î¼0 is a constant called the vacuum permeability, measuring 4ÏÃ10â7VÂ·s/ and Î¸ is the angle between H and m.
Mathematically, the torque Ï on a small magnet is proportional both to the applied magnetic field and to the magnetic moment m of the magnet:
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