Electric and Magnetic Forces in Everyday Life
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The Lorentz Force
CLASSICAL CONCEPT REVIEW 14 The Lorentz Force We can find empirically that a particle with mass m and electric charge q in an elec- tric field E experiences a force FE given by FE = q E LF-1 It is apparent from Equation LF-1 that, if q is a positive charge (e.g., a proton), FE is parallel to, that is, in the direction of E and if q is a negative charge (e.g., an electron), FE is antiparallel to, that is, opposite to the direction of E (see Figure LF-1). A posi- tive charge moving parallel to E or a negative charge moving antiparallel to E is, in the absence of other forces of significance, accelerated according to Newton’s second law: q F q E m a a E LF-2 E = = 1 = m Equation LF-2 is, of course, not relativistically correct. The relativistically correct force is given by d g mu u2 -3 2 du u2 -3 2 FE = q E = = m 1 - = m 1 - a LF-3 dt c2 > dt c2 > 1 2 a b a b 3 Classically, for example, suppose a proton initially moving at v0 = 10 m s enters a region of uniform electric field of magnitude E = 500 V m antiparallel to the direction of E (see Figure LF-2a). How far does it travel before coming (instanta> - neously) to rest? From Equation LF-2 the acceleration slowing the proton> is q 1.60 * 10-19 C 500 V m a = - E = - = -4.79 * 1010 m s2 m 1.67 * 10-27 kg 1 2 1 > 2 E > The distance Dx traveled by the proton until it comes to rest with vf 0 is given by FE • –q +q • FE 2 2 3 2 vf - v0 0 - 10 m s Dx = = 2a 2 4.79 1010 m s2 - 1* > 2 1 > 2 Dx 1.04 10-5 m 1.04 10-3 cm Ϸ 0.01 mm = * = * LF-1 A positively charged particle in an electric field experiences a If the same proton is injected into the field perpendicular to E (or at some angle force in the direction of the field. -
Measuring Electricity Voltage Current Voltage Current
Measuring Electricity Electricity makes our lives easier, but it can seem like a mysterious force. Measuring electricity is confusing because we cannot see it. We are familiar with terms such as watt, volt, and amp, but we do not have a clear understanding of these terms. We buy a 60-watt lightbulb, a tool that needs 120 volts, or a vacuum cleaner that uses 8.8 amps, and dont think about what those units mean. Using the flow of water as an analogy can make Voltage electricity easier to understand. The flow of electrons in a circuit is similar to water flowing through a hose. If you could look into a hose at a given point, you would see a certain amount of water passing that point each second. The amount of water depends on how much pressure is being applied how hard the water is being pushed. It also depends on the diameter of the hose. The harder the pressure and the larger the diameter of the hose, the more water passes each second. The flow of electrons through a wire depends on the electrical pressure pushing the electrons and on the Current cross-sectional area of the wire. The flow of electrons can be compared to the flow of Voltage water. The water current is the number of molecules flowing past a fixed point; electrical current is the The pressure that pushes electrons in a circuit is number of electrons flowing past a fixed point. called voltage. Using the water analogy, if a tank of Electrical current (I) is defined as electrons flowing water were suspended one meter above the ground between two points having a difference in voltage. -
Chapter 22 Magnetism
Chapter 22 Magnetism 22.1 The Magnetic Field 22.2 The Magnetic Force on Moving Charges 22.3 The Motion of Charged particles in a Magnetic Field 22.4 The Magnetic Force Exerted on a Current- Carrying Wire 22.5 Loops of Current and Magnetic Torque 22.6 Electric Current, Magnetic Fields, and Ampere’s Law Magnetism – Is this a new force? Bar magnets (compass needle) align themselves in a north-south direction. Poles: Unlike poles attract, like poles repel Magnet has NO effect on an electroscope and is not influenced by gravity Magnets attract only some objects (iron, nickel etc) No magnets ever repel non magnets Magnets have no effect on things like copper or brass Cut a bar magnet-you get two smaller magnets (no magnetic monopoles) Earth is like a huge bar magnet Figure 22–1 The force between two bar magnets (a) Opposite poles attract each other. (b) The force between like poles is repulsive. Figure 22–2 Magnets always have two poles When a bar magnet is broken in half two new poles appear. Each half has both a north pole and a south pole, just like any other bar magnet. Figure 22–4 Magnetic field lines for a bar magnet The field lines are closely spaced near the poles, where the magnetic field B is most intense. In addition, the lines form closed loops that leave at the north pole of the magnet and enter at the south pole. Magnetic Field Lines If a compass is placed in a magnetic field the needle lines up with the field. -
Equivalence of Current–Carrying Coils and Magnets; Magnetic Dipoles; - Law of Attraction and Repulsion, Definition of the Ampere
GEOPHYSICS (08/430/0012) THE EARTH'S MAGNETIC FIELD OUTLINE Magnetism Magnetic forces: - equivalence of current–carrying coils and magnets; magnetic dipoles; - law of attraction and repulsion, definition of the ampere. Magnetic fields: - magnetic fields from electrical currents and magnets; magnetic induction B and lines of magnetic induction. The geomagnetic field The magnetic elements: (N, E, V) vector components; declination (azimuth) and inclination (dip). The external field: diurnal variations, ionospheric currents, magnetic storms, sunspot activity. The internal field: the dipole and non–dipole fields, secular variations, the geocentric axial dipole hypothesis, geomagnetic reversals, seabed magnetic anomalies, The dynamo model Reasons against an origin in the crust or mantle and reasons suggesting an origin in the fluid outer core. Magnetohydrodynamic dynamo models: motion and eddy currents in the fluid core, mechanical analogues. Background reading: Fowler §3.1 & 7.9.2, Lowrie §5.2 & 5.4 GEOPHYSICS (08/430/0012) MAGNETIC FORCES Magnetic forces are forces associated with the motion of electric charges, either as electric currents in conductors or, in the case of magnetic materials, as the orbital and spin motions of electrons in atoms. Although the concept of a magnetic pole is sometimes useful, it is diácult to relate precisely to observation; for example, all attempts to find a magnetic monopole have failed, and the model of permanent magnets as magnetic dipoles with north and south poles is not particularly accurate. Consequently moving charges are normally regarded as fundamental in magnetism. Basic observations 1. Permanent magnets A magnet attracts iron and steel, the attraction being most marked close to its ends. -
Permanent Magnet Design Guidelines
NOTE(2019): THIS ORGANIZATION (MMPA) IS OBSOLETE! MAGNET GUIDELINES Basic physics of magnet materials II. Design relationships, figures merit and optimizing techniques Ill. Measuring IV. Magnetizing Stabilizing and handling VI. Specifications, standards and communications VII. Bibliography INTRODUCTION This guide is a supplement to our MMPA Standard No. 0100. It relates the information in the Standard to permanent magnet circuit problems. The guide is a bridge between unit property data and a permanent magnet component having a specific size and geometry in order to establish a magnetic field in a given magnetic circuit environment. The MMPA 0100 defines magnetic, thermal, physical and mechanical properties. The properties given are descriptive in nature and not intended as a basis of acceptance or rejection. Magnetic measure- ments are difficult to make and less accurate than corresponding electrical mea- surements. A considerable amount of detailed information must be exchanged between producer and user if magnetic quantities are to be compared at two locations. MMPA member companies feel that this publication will be helpful in allowing both user and producer to arrive at a realistic and meaningful specifica- tion framework. Acknowledgment The Magnetic Materials Producers Association acknowledges the out- standing contribution of Parker to this and designers and manufacturers of products usingpermanent magnet materials. Parker the Technical Consultant to MMPA compiled and wrote this document. We also wish to thank the Standards and Engineering Com- mittee of MMPA which reviewed and edited this document. December 1987 3M July 1988 5M August 1996 December 1998 1 M CONTENTS The guide is divided into the following sections: Glossary of terms and conversion A very important starting point since the whole basis of communication in the magnetic material industry involves measurement of defined unit properties. -
F = BIL (F=Force, B=Magnetic Field, I=Current, L=Length of Conductor)
Magnetism Joanna Radov Vocab: -Armature- is the power producing part of a motor -Domain- is a region in which the magnetic field of atoms are grouped together and aligned -Electric Motor- converts electrical energy into mechanical energy -Electromagnet- is a type of magnet whose magnetic field is produced by an electric current -First Right-Hand Rule (delete) -Fixed Magnet- is an object made from a magnetic material and creates a persistent magnetic field -Galvanometer- type of ammeter- detects and measures electric current -Magnetic Field- is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. -Magnetic Flux- is a measure of the amount of magnetic B field passing through a given surface -Polarized- when a magnet is permanently charged -Second Hand-Right Rule- (delete) -Solenoid- is a coil wound into a tightly packed helix -Third Right-Hand Rule- (delete) Major Points: -Similar magnetic poles repel each other, whereas opposite poles attract each other -Magnets exert a force on current-carrying wires -An electric charge produces an electric field in the region of space around the charge and that this field exerts a force on other electric charges placed in the field -The source of a magnetic field is moving charge, and the effect of a magnetic field is to exert a force on other moving charge placed in the field -The magnetic field is a vector quantity -We denote the magnetic field by the symbol B and represent it graphically by field lines -These lines are drawn ⊥ to their entry and exit points -They travel from N to S -If a stationary test charge is placed in a magnetic field, then the charge experiences no force. -
Electric and Magnetic Fields the Facts
PRODUCED BY ENERGY NETWORKS ASSOCIATION - JANUARY 2012 electric and magnetic fields the facts Electricity plays a central role in the quality of life we now enjoy. In particular, many of the dramatic improvements in health and well-being that we benefit from today could not have happened without a reliable and affordable electricity supply. Electric and magnetic fields (EMFs) are present wherever electricity is used, in the home or from the equipment that makes up the UK electricity system. But could electricity be bad for our health? Do these fields cause cancer or any other disease? These are important and serious questions which have been investigated in depth during the past three decades. Over £300 million has been spent investigating this issue around the world. Research still continues to seek greater clarity; however, the balance of scientific evidence to date suggests that EMFs do not cause disease. This guide, produced by the UK electricity industry, summarises the background to the EMF issue, explains the research undertaken with regard to health and discusses the conclusion reached. Electric and Magnetic Fields Electric and magnetic fields (EMFs) are produced both naturally and as a result of human activity. The earth has both a magnetic field (produced by currents deep inside the molten core of the planet) and an electric field (produced by electrical activity in the atmosphere, such as thunderstorms). Wherever electricity is used there will also be electric and magnetic fields. Electric and magnetic fields This is inherent in the laws of physics - we can modify the fields to some are inherent in the laws of extent, but if we are going to use electricity, then EMFs are inevitable. -
Lecture 8: Magnets and Magnetism Magnets
Lecture 8: Magnets and Magnetism Magnets •Materials that attract other metals •Three classes: natural, artificial and electromagnets •Permanent or Temporary •CRITICAL to electric systems: – Generation of electricity – Operation of motors – Operation of relays Magnets •Laws of magnetic attraction and repulsion –Like magnetic poles repel each other –Unlike magnetic poles attract each other –Closer together, greater the force Magnetic Fields and Forces •Magnetic lines of force – Lines indicating magnetic field – Direction from N to S – Density indicates strength •Magnetic field is region where force exists Magnetic Theories Molecular theory of magnetism Magnets can be split into two magnets Magnetic Theories Molecular theory of magnetism Split down to molecular level When unmagnetized, randomness, fields cancel When magnetized, order, fields combine Magnetic Theories Electron theory of magnetism •Electrons spin as they orbit (similar to earth) •Spin produces magnetic field •Magnetic direction depends on direction of rotation •Non-magnets → equal number of electrons spinning in opposite direction •Magnets → more spin one way than other Electromagnetism •Movement of electric charge induces magnetic field •Strength of magnetic field increases as current increases and vice versa Right Hand Rule (Conductor) •Determines direction of magnetic field •Imagine grasping conductor with right hand •Thumb in direction of current flow (not electron flow) •Fingers curl in the direction of magnetic field DO NOT USE LEFT HAND RULE IN BOOK Example Draw magnetic field lines around conduction path E (V) R Another Example •Draw magnetic field lines around conductors Conductor Conductor current into page current out of page Conductor coils •Single conductor not very useful •Multiple winds of a conductor required for most applications, – e.g. -
Chapter 7 Electricity Lesson 2 What Are Static and Current Electricity?
Chapter 7 Electricity Lesson 2 What Are Static and Current Electricity? Static Electricity • Most objects have no charge= the atoms are neutral. • They have equal numbers of protons and electrons. • When objects rub against another, electrons move from the atoms of one to atoms of the other object. • The numbers of protons and electrons in the atoms are no longer equal: they are either positively or negatively charged. • The buildup of charges on an object is called static electricity. • Opposite charges attract each other. • Charged objects can also attract neutral objects. • When items of clothing rub together in a dryer, they can pick up a static charge. • Because some items are positive and some are negative, they stick together. • When objects with opposite charges get close, electrons sometimes jump from the negative object to the positive object. • This evens out the charges, and the objects become neutral. • The shocks you can feel are called static discharge. • The crackling noises you hear are the sounds of the sparks. • Lightning is also a static discharge. • Where does the charge come from? • Scientists HYPOTHESIZE that collisions between water droplets in a cloud cause the drops to become charged. • Negative charges collect at the bottom of the cloud. • Positive charges collect at the top of the cloud. • When electrons jump from one cloud to another, or from a cloud to the ground, you see lightning. • The lightning heats the air, causing it to expand. • As cooler air rushes in to fill the empty space, you hear thunder. • Earth can absorb lightning’s powerful stream of electrons without being damaged. -
Glossary Module 1 Electric Charge
Glossary Module 1 electric charge - is a basic property of elementary particles of matter. The protons in an atom, for example, have positive charge, the electrons have negative charge, and the neutrons have zero charge. electrostatic force - is one of the most powerful and fundamental forces in the universe. It is the force a charged object exerts on another charged object. permittivity – is the ability of a substance to store electrical energy in an electric field. It is a constant of proportionality that exists between electric displacement and electric field intensity in a given medium. vector - a quantity having direction as well as magnitude. Module 2 electric field - a region around a charged particle or object within which a force would be exerted on other charged particles or objects. electric flux - is the measure of flow of the electric field through a given area. Module 3 electric potential - the work done per unit charge in moving an infinitesimal point charge from a common reference point (for example: infinity) to the given point. electric potential energy - is a potential energy (measured in joules) that results from conservative Coulomb forces and is associated with the configuration of a particular set of point charges within a defined system. Module 4 Capacitance - is a measure of the capacity of storing electric charge for a given configuration of conductors. Capacitor - is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field. Dielectric - a medium or substance that transmits electric force without conduction; an insulator. Module 5 electric current - is a flow of charged particles. -
Electricity and Circuits
WHAT IS ELECTRICITY? Before we can understand what electricity is, we need to know a little about atoms. Atoms are made up of three different types of particle: protons, neutrons, and electrons. Protons have a positive charge, neutrons are neutral, and electrons are negative charged. An atom can become positive or negatively charged by losing or gaining electrons. If an atom losses an electron it becomes positively charged. If an atom gains an electron it becomes negatively charged. WHAT IS ELECTRICITY? Electricity is a force due to charged particles. This can be static electricity, in which charged particles gather. Current, or the flow of charged particles, is also a form of electricity. Current is the ordered flow of charged particles. Often current flows through a wire. This is how we get the electricity we use everyday! WHAT ARE CIRCUITS? A circuit is a path that electric current flows around. Current flows from a power source to a load. The load converts the electric energy into anther type of energy A light bulb is a load that converts electrical energy into light and heat energy. What are some other types of loads? What type of energy do they convert the electric energy into? WIRES Why are circuits connected with wires? Wires are made out of metal which is a conductive material. A conductive material is one that electricity can travel through easily. Which of these material are conductive? Water (dirty) Wood Aluminum Foil Glass String Graphite Styrofoam Concrete Cotton (fabric) Air OPEN VS. CLOSED CIRCUIT CLOSED! OPEN! Why didn’t the light bulb turn on in the open circuit? In the open circuit the current can not flow from one end of the power source to the other. -
Electric Current and Electrical Energy
Unit 9P.2: Electricity and energy Electric Current and Electrical Energy What Is Electric Current? We use electricity every day to watch TV, use a Write all the computer, or turn on a light. Electricity makes all of vocab words you these things work.Electrical energy is the energy of find in BOLD electric charges. In most of the things that use electrical energy, the charges(electrons) flow through wires. As per the text The movement of charges is called an electric current. Electric currents provide the energy to things that use electrical energy. We talk about electric current in units called amperes, or amps.The symbol for ampere is A. In equations, the symbol for current is the letter I. AC AND DC There are two kinds of electric current—direct current (DC) and alternating current (AC). In the figure below you can see that in direct current, the charges always flow in the same direction. In alternating current, the direction of the charges continually changes. It moves in one direction, then in the opposite direction. The electric current from the batteries in a camera or Describe What kind of a flashlight is DC. The current from outlets in your current makes a home is AC. Both kinds of current give you electrical refrigerator energy. run and in what direction What Is Voltage? do the charges move? If you are on a bike at the top of a hill, you can roll Alternating current makes a down to the bottom. This happens because of the refrigerator run. difference in height between the two points.