The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. The forces acting on the moving charges in a conductor in a magnetic field is strikingly demonstrated by the Hall effect, an effect analogous to the transverse deflection of an electron beam in a magnetic field in vacuum. (The effect was discoveredby the American physicist Edwin Hall in 1879 while he was still a graduate student.) To describe this effect, let’s consider a conductor in the form of a flat strip. The current is in the direction of the +x-axis, and there is a uniform magnetic field B perpendicular to the plane of the strip, …show more content…
T10.1b shows positive charges. In both cases the magnetic force is upward, just as the magnetic force on a conductor is the same whether the moving charges are positive or negative. In either case a moving charge is driven toward the upper edge of the strip by the magnetic force Fz = |q|vdB. If the charge carriers are electrons, an excess negative charge accumulates at the upper edge of the strip, leaving an excess positive charge at its lower edge. This accumulation continues until the resulting transverse electrostatic field E becomes large enough to cause a force (magnitude |q|E) that is equal and opposite to the magnetic force (magnitude |q|vd B). After that, there is no longer any net transverse force to deflect the moving charges. This electric field causes a transverse potential difference between opposite edges of the strip, called the Hall voltage or the Hall emf. The polarity depends on whether the moving charges are positive or negative. Experiments show that for metals the upper edge of the strip in Fig. T10.1a does become negatively charged, showing that the charge carriers in a metal are indeed negative …show more content…
These materials conduct by a process known as hole conduction. Within such a material there are locations, called holes, that would normally be occupied by an electron but are actually empty. A missing negative charge is equivalent to a positive charge. When an electron moves in one direction to fill a hole, it leaves another hole behind it. The hole migrates in the direction opposite to that of the electron. In terms of the coordinate axes in Fig. T10.1b, the electrostatic field E for the positive-q case is in the −z-direction; its z-component Ez is negative. The magnetic field is in the +y-direction, and we write it as By . The magnetic force (in the +zdirection) is qvd By. The current density Jx is in the +x-direction. In the steady state, when the forces qEz and qvdBy are equal in magnitude and opposite in direction, This confirms that when q is positive, Ez is negative. The current density Jx is Eliminating vd between these equations, we find (T10.1) Note that this result (as well as the entire derivation) is valid for both positive and negative q. When q is negative, Ez is positive, and conversely. We can measure Jx , By , and Ez, so we can compute the product nq. In both metals and semiconductors, q is equal in magnitude to the electron charge, so
He knew this because polar opposites attract to each other and polars of the same push away from each other. In both the test with electromagnets and the normal magnet he had observed that the beam would curve inside the tube towards the positively charged metal and propel from the negatively charged metal. If polar opposites attract and the beam attracts to the positive, then it must be a negatively charged beam of
For examining the influence of age and gender on the Stroop effect, the experimenter adopted the Stroop paradigm. In Stroop paradigm there are three: neutral or control, congruent and incongruent groups. Neutral / control group will receive stimuli in which only the text or colors are presented (van Maanen L, van Rijn H& Borst JP, 2009). When the color of the word and the text of the word refer to the same color (for example the word "red" printed in red) is a congruent stimulus. In Incongruent stimulus, the color of the word and color of the text differ (for example the word "red" printed in blue).
Eli Whitney was born on the eighth of December in the year 1765 in Westborough, Massachusetts. He was known as an engineer and manufacturer; however more importantly he was known as “the third-best American inventor during the pre-atomic age” (Inventor of the Week). Even as a child Whitney showed interest in machinery. During Whitney’s youth, he invented the nail-making machine, and later in life he devised the first milling machine, pain lessening devices for himself, and the idea of interchangeable parts, and “the father of the mass production method” (Whitney Museum). Although he invented a wide variety of machines and devices, the invention of the cotton gin (short for cotton engine) is what he is most known for.
Metals contain a sea of electrons (which are negatively charged) and which flow throughout the metal. This is what allows electric current to flow so well in all metals. An electrode is a component of an electric circuit that connects the wiring of the circuit to a gas or electrolyte. A compound that conducts in a solution is called an electrolyte. The electrically positive electrode is called the anode and the negative electrode the cathode.
Nathaniel Hall one of the kids in the book True notebooks that were in Mark Salzman’s class stood out to me to me the most because he was showing signs of changing, but he is also manipulative and shows signs of not changing at all, the juvenile system was not effective enough at supporting Nathaniel’s change it failed to bring him up to his high potential, if he had stayed in the juvenile spending more time with Mark at the writing workshop and not transferred to the penitentiary he would have probably turned out to be okay. Nathaniel is so high-spiritedness even though he is obviously struggling with his past life he lived when he was on the streets. It’s like he is hiding something through all his rhymes and high spirit. He kind of confuses me because he sometimes talks about becoming a new person and how the writing has changed him then other times about going back to his gang once he gets out because that’s the only life he can relate to describing it as real. Nathaniel Hall, as brilliant as he may
...rting out, Tesla devised a “Spark Gap” which discharges sparks between two electrodes. The gap should be adjustable as to control the amount of voltage that crosses it at one given time.
A direct current in a set of windings creates a polar magnetic field. A torque acts on the rotor due to its relation to the external magnetic field. Just as the magnetic field of the rotor becomes fully aligned with the external magnetic field, the direction of the current in the windings on the armature reverses, thereby reversing the polarity of the rotor's electromagnetic field. A torque is once again exerted on the rotor, and it continues spinning.
... middle of paper ... ... conductor is moving parallel to the field; hence, no voltage is generated.
First off, what is current. Current is expressed in a unit called Amps. Amps are a measurement of how many electrons pass per second. That is to say, a wire with 40 coulombs passing any point in a 2 seconds would be said to have 20 Amps of current (40 Coulombs (a unit of charge given as 6.24x1018 electrons) / time in seconds or in this case, 2 seconds. The Amp is also known as Coulombs per second) Another trick about current is that it is measured in the movement of the positive charge. Literally that is to say the current moves in oppostion to the electrons. This is because originally it was thought that the positive charge is what moved, both are viable, but in reality a positive charge is generally fixed since within an atom the electrons are migratory, while the protons and neutrons tend to be stationary.
Grundmann, Marius. Physics of Semiconductors: An Introduction Including Devices and Nanophysics. New York: Springer, 2006. Print.
The “head”, or device used to transmit data onto the magnetic disks, is an important part of the hard disk and composes most of the physics happenings. Current is passed through the head or in the physic’s case, the conductor, to produce a magnetic field around the conductor. This magnetic field then can influence the disk’s magnetic material. The head is driven by an electric motor, using electromagnetism, to exert pushing and pulling forces on magnets to the rotating shaft. In some cases the head moves to a required area on the disk, and the motion of the magnetized surface induces tiny voltage. This voltage is concentrated in the coil of the read head, and can be interpreted as the data stored on the magnetic disk. When the direction of the flow of electric current is reversed, the magnetic field’s polarity is reversed.
Electric currents produce magnetic fields, they can be as small as macroscopic currents in wires, or microscopic currents in atomic orbits caused by electrons. The magnetic field B is described in terms of force on a moving charge in the Lorentz force law. The relationship of magnetic field and charges leads to many practical applications. Magnetic field sources are dipolar in nature, with a north and south magnetic pole. The magnetic field SI unit is the Tesla, it can be seen in the magnetic part of the Lorentz force law F magnetic = qvB composed of (Newton x second)/(Coulomb x meter). The smaller magnetic field unit is the
The Earth’s magnetic field is a major component to exploring the earth. The north and the south poles have always been a guide for travelers. Using compasses, the direction of the north pole and the south pole has always been provided by the magnetic force of the magnetic field. What many people do not know though is the earth’s magnetic field provides way more than that. The magnetic field, also known as the magnetosphere, protects us from all kinds of harmful substances. Some of these substances include solar wind and harmful radiation from the sun. The magnetosphere also protects the atmosphere, which protects us.
The phenomenon called electromagnetic induction was first noticed and investigated by Michael Faraday, in 1831. Electromagnetic induction is the production of an electromotive force (emf) in a conductor as a result of a changing magnetic field about the conductor and is a very important concept. Faraday discovered that, whenever the magnetic field about an electromagnet was made to grow and collapse by closing and opening the electric circuit of which it was a part, an electric current could be detected in a separate conductor nearby. Faraday also investigated the possibility that a current could be produced by a magnetic field being placed near a coiled wire. Just placing the magnet near the wire could not produce a current. Faraday discovered that a current could be produced in this situation only if the magnet had some velocity. The magnet could be moved in either a positive or negative direction but had to be in motion to produce any current in the wire. The current in the coil is called an induced current, because the current is brought about (or “induced”) by a changing magnetic field (Cutnell and Johnson 705). The induced current is sustained by an emf. Since a source of emf is always needed to produce a current, the coil itself behaves as if it were a source of emf. The emf is known as an induced emf. Thus, a changing magnetic field induces an emf in the coil, and the emf leads to an induced current (705). He also found that moving a conductor near a stationary permanent magnet caused a current to flow in the wire as long as it was moving as in the magnet and coiled wire set-up.
In 1831, using his "induction ring", Faraday made one of his greatest discoveries - electromagnetic induction: the "induction" or generation of electricity in a wire by means of the electromagnetic effect of a current in another wire. The induction ring was the first electric transformer. In a second series of experiments in September he discovered magneto-electric induction: the production of a steady electric current. To do this, Faraday attached two wires through a sliding contact to a copper disc. By rotating the disc between the poles of a horseshoe magnet he obtained a continuous direct current. This was the first generator. From his experiments came devices that led to the modern electric motor, generator and transformer.