3.2.1 Force on a Charged Particle (Moving Charge) In chapter two, we discussed that the electric force F, on a stationary o oving electric charge Q n an electric field is given by Coulomb's law and is related to the electr cld intensity E as (21: F= QE (8.1)

Power System Analysis and Design (MindTap Course List)
6th Edition
ISBN:9781305632134
Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma
Chapter6: Power Flows
Section: Chapter Questions
Problem 6.27P
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8.1 INTRODUCTION
8.2 FORCES DUE TO MAGNETIC FIELDS
There are at least three ways in which force due to magnetic fields can be experienced, The force
can be [2].
• due to a
narticle in a B field,
na current element in an exten
Lor
between two current elements.
8.2.1 Force on a Charged Particle (Moving Charge)
In chapter two, we discussed that the electric force F, on a stationary o oving electric charge Q
in an electric field is given by Coulomb's law and is related to the electri eld intensity E as (2):
F = QE
(8.1)
that if Q is positive, F and E have the sam
on and F, is directly proportional
to both E and QTI
A magnetic field can exert force only on a moving charge. From experiments, it is found that the
magnetic force Fm experienced by a charge Q moving with a velocity u in a magnetic field B is
[2):
F = Qu x B
(8.2)
%3D
The force F has direction perpendicular to both u and B and whose magnitude is proportional
to the product of the magnitudes of the charge Q, its velocity u, the flux density B, and to the
sine of the angle between the vectors u and B [1].-
.
A comparison between the electric force and the magnetic force can be made [2].
• The electric force F, is independent of the velocity of the charge.
• The electric force E can perform work on the charge and change its kinetic energy.
The magnetic force F depends on the charge velocity and is normal to it.
• The magnetic force F cannot perform work because it is at right angles to the direction
of motion of the charge (Fn dL = 0); it does not cause an increase in kinetic energy of
the charge.
The magnitude of E is generally small compared to F, except at high velocities.
31
Chapter 8:
Magnetic Forces, Materials, and Devices
For a moving charge Q in the presence of both electric and magnetic fields, the total force on the
charge is given by superposition [2].
F = F, + E = Q E+ Qu x B
F = Q (E + ux B)
(8.3)
This equation is known as the Lorentz force equation, and its solution is required in determining
electron orbits in the magnetron, proton paths in the cyclotron, plasma characteristics in a
magneto-hydrodynamic (MHD) generator, or, in general, charged-particle motion in combined
clectric and magnetic fields | 1).
Lorentz force equation relates mechanical force to electrical force. If the mass of the charged
.
particle moving in E and B fields is (m), by Newton's second law of motion [2].
du
F =m = ma = Q (E + ux B)
dt
(8.4)
Table (8.1) Force on a Charged Particle
No.
State of D
ie Field
Magnetic Field
Combined E and B Fields
stationary
QE
QE
----
Moving
QE
Q (E +ux B)
8.2.2 Force on a Differential Current Element.
The force on a charged particle moving through a steady mae field may be written as the
Lforce exerted on a differential
Carge |1).
dF = dQu x B
(8.5)
The force on a current element (IdL) of a current-carrying conductor due to the magnetic field,
can be determined by using the fact that for convection current density [2]:
Transcribed Image Text:8.1 INTRODUCTION 8.2 FORCES DUE TO MAGNETIC FIELDS There are at least three ways in which force due to magnetic fields can be experienced, The force can be [2]. • due to a narticle in a B field, na current element in an exten Lor between two current elements. 8.2.1 Force on a Charged Particle (Moving Charge) In chapter two, we discussed that the electric force F, on a stationary o oving electric charge Q in an electric field is given by Coulomb's law and is related to the electri eld intensity E as (2): F = QE (8.1) that if Q is positive, F and E have the sam on and F, is directly proportional to both E and QTI A magnetic field can exert force only on a moving charge. From experiments, it is found that the magnetic force Fm experienced by a charge Q moving with a velocity u in a magnetic field B is [2): F = Qu x B (8.2) %3D The force F has direction perpendicular to both u and B and whose magnitude is proportional to the product of the magnitudes of the charge Q, its velocity u, the flux density B, and to the sine of the angle between the vectors u and B [1].- . A comparison between the electric force and the magnetic force can be made [2]. • The electric force F, is independent of the velocity of the charge. • The electric force E can perform work on the charge and change its kinetic energy. The magnetic force F depends on the charge velocity and is normal to it. • The magnetic force F cannot perform work because it is at right angles to the direction of motion of the charge (Fn dL = 0); it does not cause an increase in kinetic energy of the charge. The magnitude of E is generally small compared to F, except at high velocities. 31 Chapter 8: Magnetic Forces, Materials, and Devices For a moving charge Q in the presence of both electric and magnetic fields, the total force on the charge is given by superposition [2]. F = F, + E = Q E+ Qu x B F = Q (E + ux B) (8.3) This equation is known as the Lorentz force equation, and its solution is required in determining electron orbits in the magnetron, proton paths in the cyclotron, plasma characteristics in a magneto-hydrodynamic (MHD) generator, or, in general, charged-particle motion in combined clectric and magnetic fields | 1). Lorentz force equation relates mechanical force to electrical force. If the mass of the charged . particle moving in E and B fields is (m), by Newton's second law of motion [2]. du F =m = ma = Q (E + ux B) dt (8.4) Table (8.1) Force on a Charged Particle No. State of D ie Field Magnetic Field Combined E and B Fields stationary QE QE ---- Moving QE Q (E +ux B) 8.2.2 Force on a Differential Current Element. The force on a charged particle moving through a steady mae field may be written as the Lforce exerted on a differential Carge |1). dF = dQu x B (8.5) The force on a current element (IdL) of a current-carrying conductor due to the magnetic field, can be determined by using the fact that for convection current density [2]:
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