The hall Effect

When current runs v a wire exposed come a magnetic field a potential is produced throughout the conductor that is transverse to the current.

You are watching: When no current flows in a conductor, free electrons move ? , and their magnetic fields cancel.


Key Takeaways

Key PointsThe Hall result is the phenomenon in i beg your pardon a voltage difference (called the hall voltage) is produced across an electrical conductor that is transverse to the conductor’s electric present when a magnetic field perpendicular come the conductor’s existing is applied.Moving charges in a cable will readjust trajectory in the presence of a magnetic field, “bending” toward it. Thus, those charges accumulate top top one confront of the material. Top top the various other face, over there is left an overabundance of opposite charge. Thus, an electric potential is created.\\textV_\\textH=- \\frac \\textIB\\textnetis the formula for room voltage (VH). It is a aspect of current (I), magnetic field (B), thickness the the conductor plate (t), and charge carrier density (n) that the transport electrons.Key Termselementary charge: The electrical charge on a single proton.transverse: not tangent, so the a nondegenerate edge is formed in between the two things intersecting.

The Hall result is the phenomenon in which a voltage distinction (called the hall voltage) is produced throughout an electric conductor, transverse to the conductor’s electric present when a magnetic field perpendicular come the conductor’s current is applied.

When a magnetic field is existing that is no parallel come the motion of moving charges within a conductor, the charges suffer the Lorentz force. In the absence of together a field, the charges follow a around straight path, occasionally colliding v impurities.

In the presence of a magnetic ar with a perpendicular component, the paths charges take becomes curved such the they accumulate ~ above one challenge of the material. Top top the other face, there is an overabundance of opposite charge remaining. Thus, an electric potential is produced so lengthy as the fee flows. This opposes the magnetic force, ultimately to the suggest of cancelation, leading to electron flow in a straight path.


Hall effect for Electrons: Initially, the electrons are attracted by the magnetic force and follow the curved arrow. Eventually, as soon as electrons accumulate in excess on the left side and also are in deficit top top the right, an electrical field ξy is created. This force becomes solid enough come cancel the end the magnetic force, so future electrons follow a right (rather than curved) path.


For a metal containing just one form of fee carrier (electrons), the hall voltage (VH) can be calculated as a element of present (I), magnetic field (B), thickness of the conductor bowl (t), and charge carrier density (n) of the carrier electrons:

\\textV_\\textH=- \\frac \\textIB\\textnet

In this formula, e represents the primary school charge.

The hall coefficient (RH) is a characteristic of a conductor’s material, and is characterized as the ratio of induced electric field (Ey) to the product of current density (jx) and also applied magnetic ar (B):

\\textR_\\textH=\\frac \\textE_\\texty\\textj_\\textxB=\\frac \\textV_\\textHt\\textIB=-\\frac 1\\textne

The Hall impact is a rather ubiquitous phenomenon in physics, and also appears not just in conductors, however semiconductors, ionized gases, and in quantum spin among other applications.


Magnetic pressure on a Current-Carrying Conductor

When an electric wire is exposed to a magnet, the existing in the wire will endure a force—the an outcome of a magnet field.


Learning Objectives

Express equation provided to calculate the magnetic force for an electric wire exposed to a magnetic field


Key Takeaways

Key PointsMagnetic pressure on current can be found by summing the magnetic pressure on every of the individual charges the make this current.For a cable exposed to a magnetic field,\\textF=\\textIlB \\sin \\thetadescribes the relationship in between magnetic pressure (F), present (I), length of cable (l), magnetic ar (B), and angle between field and wire (θ).The direction the the magnetic force can be established using the right hand rule, together in fig <<17951>>.Key Termsdrift velocity: The mean velocity the the complimentary charges in a conductor.magnetic field: A problem in the room around a magnet or electric present in which there is a detectable magnetic force, and also where 2 magnetic poles space present.

When an electric wire is exposed come a magnet, the existing in that wire will be impacted by a magnetic field. The result comes in the form of a force. The expression for magnetic force on existing can be discovered by summing the magnetic pressure on each of the plenty of individual fees that consist of the current. Since they all run in the very same direction, the forces can it is in added.


Right Hand Rule: supplied to identify direction that magnetic force.


The pressure (F) a magnetic ar (B) exerts on an individual charge (q) travel at drift velocity vd is:

\\textF=\\textqv_\\textdB \\sin \\theta

In this instance, θ to represent the angle in between the magnetic field and also the wire (magnetic pressure is frequently calculated together a overcome product). If B is consistent throughout a wire, and is 0 elsewhere, then because that a wire with N fee carriers in its full length l, the complete magnetic force on the cable is:

\\textF=\\textNqv_\\textdB \\sin \\theta.

Given that N=nV, wherein n is the variety of charge carriers every unit volume and V is volume of the wire, and that this volume is calculated as the product the the one cross-sectional area A and also length (V=Al), yields the equation:

\\textF=(\\textnqAv_\\textd)\\textlB \\sin \\theta.

The state in parentheses space equal to current (I), and also thus the equation have the right to be rewritten as:

\\textF=\\textIlB \\sin \\theta

The direction the the magnetic pressure can be determined using the right hand rule, demonstrated in. The thumb is pointing in the direction of the current, with the four other fingers parallel come the magnetic field. Curling the fingers reveals the direction that magnetic force.

Torque ~ above a current Loop: Rectangular and also General

A current-carrying loop exposed to a magnetic ar experiences a torque, which have the right to be supplied to strength a motor.


Learning Objectives

Identify the basic quation for the talk on a loop of any shape


Key Takeaways

Key Points\\tau=\\textNIAB \\sin \\thetacan be provided to calculation torque (\\tau) a loop that N turns and A area, transporting I present feels in the existence of a magnetic ar B.Although the pressures acting top top the loop room equal and also opposite, lock both plot to revolve the loop in the same direction.Torque proficient is elevation of the loop’s shape. What problem is the area the the loop.Key Termstorque: A rotational or twisting impact of a force; (SI unit newton-meter or Nm; royal unit foot-pound or ft-lb)

When a existing travels in a loop the is exposed to a magnetic field, that field exerts torque on the loop. This rule is typically used in motors, in i beg your pardon the loop is connected to a shaft that rotates as a result of the torque. Thus, the electric energy from the current is convert to mechanical energy as the loop and also shaft rotate, and this mechanical energy is then offered to power an additional device.


Torque on a present Loop: electric energy native the present is convert to mechanical energy as the loop and shaft rotate, and this mechanical power is then supplied to power an additional device.


In this model, the north and also south poles of magnets are denoted by N and S, respectively. In the center is a rectangle-shaped wire loop of length l and also width w, carrying existing I. The result of magnetic ar B on the current-carrying cable exerts talk τ.

To know the torque, we must analyze the pressures acting on each segment of the loop. Presume a consistent magnetic field, we deserve to conclude that the pressures on the top and also bottom components of the loop are equal in magnitude and opposite in direction, and thus develop no net force. Incidentally, those pressures are vertical and thus parallel to the shaft.

However, as depicted by (a) in the figure below, the equal but opposite forces create a torque that acts clockwise.


Varying speak on a charged loop in a magnetic field: maximum torque occurs in (b), as soon as is 90 degrees. Minimum torque is 0, and occurs in (c) when θ is 0 degrees. When loop rotates previous =0, the speak reverses (d).


Given the torque is calculated indigenous the equation:

\\tau=\\textrF \\sin \\theta

where F is force on the rotating object, r is the distance from the pivot allude that the force is applied, and also θ is the angle between r and F, we can use the sum of two torques (the forces act top top either side of the loop) to find the total torque:

\\tau=\\frac \\textw2\\textF \\sin \\theta + \\frac \\textw2\\textF \\sin \\theta = \\textwF \\sin \\theta

Note the r is equal to w/2, as illustrated.

To discover torque we still have to solve for F indigenous the magnetic ar B ~ above the current I. The rectangle has actually length l, for this reason F=IlB. Instead of F v IlB in the talk equation gives:

\\tau = \\textwIlB \\sin \\theta

Note the the product of w and l is contained in this equation; those terms can be changed with area (A) of the rectangle. If an additional shape of wire is used, that area can be inserted in the equation nevertheless of shape (whether circular, square, or otherwise).

Also note that this equation of speak is because that a solitary turn. Torque boosts proportionally follow to number of turns (N). Thus, the general equation for torque on a loop of any shape, that N turns, each of A area, transporting I current and exposed to a magnetic ar B is a worth that fluctuates together the loop rotates, and also can it is in calculated by:

\\tau=\\textNIAB \\sin \\theta


Ampere’s Law: Magnetic Field because of a long Straight Wire

Current running with a cable will produce a magnetic ar that have the right to be calculated using the Biot-Savart Law.


Learning Objectives

Express the relationship in between the stamin of a magnetic field and also a present running through a wire in a type of equation


Key Takeaways

Key PointsAmpere ‘s regulation states that for a closed curve of length C, magnetic field (B) is connected to current (IC): \\oint_\\textC \\textBd\\ell = \\mu _0 \\textI_\\textC . In this equation, dl to represent the differential of length of cable in the curved wire, and also μ0 is the permeability of totally free space.Ampere’s Law deserve to be related to the Biot-Savart law, which holds because that a short, straight length of conductor: \\textd \\bf \\textB=\\frac \\mu_04 \\pi \\frac \\textId\\bf \\textl \\times \\bf \\textr\\textr^3. In this equation, partial magnetic field (dB) is expressed as a function of present for one infinitesimally tiny segment of cable (dl) at a suggest r distance away indigenous the conductor.After integrating, the direction of the magnetic ar according to the Biot-Savart Law can be determined using the appropriate hand rule.Key Termselectric field: A an ar of an are around a fee particle, or in between two voltages; that exerts a pressure on fee objects in its vicinity.magnetic field: A condition in the space around a magnet or electric present in which over there is a detectable magnetic force, and where two magnetic poles room present.

Current running v a cable will produce both an electrical field and a magnetic field. Because that a closeup of the door curve of length C, magnetic ar (B) is related to existing (IC) together in Ampere’s Law, stated mathematically as:

\\oint_\\textC \\textBd\\ell = \\mu _0 \\textI_\\textC


Direction that magnetic field: The direction that the magnetic field can be established by the best hand rule.


In this equation, dl to represent the differential of size of cable in the curved wire, and also μ0 is the permeability of totally free space. This have the right to be pertained to the Biot-Savart law. For a short, straight length of conductor (typically a wire) this law normally calculates partial magnetic field (dB) as a role of current for an infinitesimally tiny segment of wire (dl) at a point r street away indigenous the conductor:

\\textd \\bf \\textB=\\frac \\mu_04 \\pi \\frac \\textId\\bf \\textl \\times \\bf \\textr\\textr^3.

In this equation, the r vector deserve to be created as r̂ (the unit vector in direction the r), if the r3 hatchet in the denominator is decreased to r2 (this is merely reducing choose terms in a fraction). Integrating the ahead differential equation, us find:

\\bf \\textB=\\frac \\mu_04 \\pi \\oint_\\textC \\frac \\textId\\bf \\textl \\times \\bf \\hat\\textr\\textr^2.

This partnership holds for constant current in a directly wire, in which magnetic ar at a point due to every current facets comprising the directly wire is the same. As depicted in the direction that the magnetic ar can be figured out using the right hand rule—pointing one’s thumb in the direction that current, the curl of one’s fingers shows the direction that the magnetic field around the right wire.

Magnetic Force in between Two Parallel Conductors

Parallel wires carrying current produce far-ranging magnetic fields, which in turn produce far-reaching forces ~ above currents.


Learning Objectives

Express the magnetic pressure felt by a pair that wires in a kind of one equation


Key Takeaways

Key PointsThe ar (B1) that that existing (I1) from a wire creates can be calculated together a role of current and also wire separation (r): \\textB_1=\\frac \\mu_0\\textI_12\\pi \\textr μ0 is a constant.\\textF=\\textIlB \\sin \\theta explains the magnetic pressure felt through a pair that wires. If they room parallel the equation is streamlined as the sine function is 1.The pressure felt in between two parallel conductive wires is provided to define the ampere —the typical unit the current.Key Termsampere: A unit of electric current; the traditional base unit in the international System that Units. Abbreviation: amp. Symbol: A.current: The time price of circulation of electrical charge.magnetic field: A problem in the space around a magnet or electric existing in which over there is a detectable magnetic force, and where 2 magnetic poles are present.

Parallel wires carrying present produce far-ranging magnetic fields, which consequently produce significant forces on currents. The force felt between the wires is used to specify the the standard unit the current, understand as an amphere.

In, the ar (B1) the I1 creates can be calculated together a function of current and wire separation (r):


Magnetic fields and force exerted by parallel current-carrying wires.: Currents I1 and I2 flow in the very same direction, separated by a street of r.


\\textB_1=\\frac \\mu_0\\textI_12\\pi \\textr

The ar B1 exerts a force on the wire containing I2. In the figure, this pressure is denoted together F2.

The force F2 exerts on cable 2 can be calculated as:

\\textF_2=\\textI_2\\textlB_1 \\sin \\theta

Given the the ar is uniform along and perpendicular to cable 2, sin θ = sin 90 derees = 1. For this reason the force simplifies to: F2=I2lB1

According to Newton’s third Law (F1=-F2), the pressures on the two wires will certainly be same in magnitude and opposite in direction, for this reason to just we deserve to use F rather of F2. Provided that wires are often really long, it’s frequently convenient to deal with for force per unit length. Rearranging the ahead equation and also using the meaning of B1 gives:

\\frac \\textF\\textl=\\frac \\mu_0\\textI_1\\textI_22\\pi \\textr

If the currents are in the same direction, the force attracts the wires. If the currents space in the opposite directions, the force repels the wires.

The force between current-carrying wires is supplied as component of the operational meaning of the ampere. Because that parallel wires inserted one meter away from one another, each moving one ampere, the force per meter is:

\\frac \\textF\\textl=\\frac(4\\pi \\cdot 10^-7 \\textT \\cdot \\textm/\\textA)(1\\textA)^2(2\\pi )(1\\textm)=2 \\cdot 10^-7\\textN/\\textm

The final units come from instead of T through 1N/(A×m).

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Incidentally, this value is the basis of the operational definition of the ampere. This means that one ampere of present through 2 infinitely long parallel conductors (separated by one meter in empty space and complimentary of any type of other magnetic fields) reasons a pressure of 2×10-7 N/m on every conductor.