Electricity & Magnetism

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Electricity & Magnetism

  1. 1. Electricity &Magnetism T- 1-855-694-8886Email- info@iTutor.comBy iTutor.com
  2. 2. Fields and forces The concept of a field is used to describe anyquantity that has a value for all points in space. You can think of the field as the way forces aretransmitted between objects. Charge creates an electric field that creates forceson other charges.© iTutor. 2000-2013. All Rights Reserved
  3. 3. Fields and forces Gravitational forces are far weaker than electricforces.© iTutor. 2000-2013. All Rights Reserved
  4. 4. the electric field© iTutor. 2000-2013. All Rights Reserved
  5. 5. EMF – Electric & MagneticFields Electricity produces two types of fields; an electricfield and a magnetic field called electromagneticfields or EMF. Electric fields are created by the presence of electriccharges and are measured in volts per meter (V/m). An electric field is associated with any device orwire that is connected to a source of electricity,even when a current is not flowing.© iTutor. 2000-2013. All Rights Reserved
  6. 6. Electric fields andelectric force On the Earth’s surface, the gravitational fieldcreates 9.8 N of force on each kilogram of mass. With gravity, the strength of the field is in Newtonper kilogram (N/kg) because the field describes theamount of force per kilogram of mass.© iTutor. 2000-2013. All Rights Reserved
  7. 7. Electric fields andelectric force• With the electric field, the strength is in Newtonper coulomb (N/C).• The electric field describes the amount of force percoulomb of charge.© iTutor. 2000-2013. All Rights Reserved
  8. 8. What is a magnet?• If a material is magnetic, it has the ability toexert forces on magnets or other magneticmaterials.• A permanent magnet is a material that keeps itsmagnetic properties even when it is NOT close toother magnets.© iTutor. 2000-2013. All Rights Reserved
  9. 9. Magnetism is the properties and interactionsof magnetsMagnets produce magnetic forces and havemagnetic field linesmagnetism© iTutor. 2000-2013. All Rights Reserved
  10. 10. magnetism The magnetic field of a coil is identical to the field ofa disk-shaped permanent magnet.© iTutor. 2000-2013. All Rights Reserved
  11. 11. The force between twomagnets The strength of the forcebetween magnets dependson the distance betweenthem. The magnetic forcedecreases with distancemuch faster than doeseither gravity or theelectric force.© iTutor. 2000-2013. All Rights Reserved
  12. 12. The magnetic field All magnets create a magneticfield in the space around them,and the magnetic field createsforces on other magnets. The number of field lines in acertain area indicates therelative strength of the magneticfield in that area. The closer the lines aretogether, the stronger the field. The arrows on the field linesyndicate the direction of theforce© iTutor. 2000-2013. All Rights Reserved
  13. 13. The Magnetic Field of theEarth When you use a compass, thenorth-pointing end of theneedle points toward a spotnear (but not exactly at) theEarth’s geographic north pole. The Earth’s magnetic polesare defined by the planet’smagnetic field. That means the southmagnetic pole of the planet isnear the north geographicpole.© iTutor. 2000-2013. All Rights Reserved
  14. 14. The Magnetic Field of theEarth Depending on where you are, a compass will pointslightly east or west of true north. The difference between the direction a compasspoints and the direction of true north is calledmagnetic declination.After correcting for thedeclination, you rotate thewhole compass until thenorth-pointing end of theneedle lines up with zerodegrees on the ring.The large arrow points in thedirection you want to go.© iTutor. 2000-2013. All Rights Reserved
  15. 15. Electric Current andMagnetism Two wires carrying electric current exert force oneach other, just like two magnets. The forces can be attractive or repulsivedepending on the direction of current in bothwires.© iTutor. 2000-2013. All Rights Reserved
  16. 16. Electric Current andMagnetism The magnetic field around a single wire is toosmall to be of much use. There are two techniques to make strongmagnetic fields from current flowing in wires:1. Many wires are bundled together, allowing thesame current to create many times themagnetic field of a single wire.2. Bundled wires are made into coils whichconcentrate the magnetic field in their center.© iTutor. 2000-2013. All Rights Reserved
  17. 17. Electric Current andMagnetism The electrons movingaround the nucleus carryelectric charge. Moving charge makeselectric current so theelectrons around thenucleus create currentswithin an atom. These currents create themagnetic fields thatdetermine the magneticproperties of atoms.© iTutor. 2000-2013. All Rights Reserved
  18. 18. Magnetic force on amoving charge The magnetic force on a wire is really due to forceacting on moving charges in the wire. A charge moving in a magnetic field feels a forceperpendicular to both the magnetic field and tothe direction of motion of the charge.© iTutor. 2000-2013. All Rights Reserved
  19. 19. RIGHT HAND RULE It’s a method of determiningthe direction of Force (F),Current (I) or MagneticField (B)The direction of the force canbe deduced from the right-hand rule.If you bend the fingers of yourright hand as shown, yourthumb, index, and middlefinger indicate the directionsof the force, current andmagnetic field.© iTutor. 2000-2013. All Rights Reserved
  20. 20. RIGHT HAND RULE© iTutor. 2000-2013. All Rights Reserved
  21. 21. Magnetic force on amoving charge A magnetic field that has a strength of 1 tesla (1 T)creates a force of 1 Newton (1 N) on a charge of 1coulomb (1 C) moving at 1 meter per second. This relationship is how the unit of magnetic fieldis defined.© iTutor. 2000-2013. All Rights Reserved
  22. 22. Magnetic force on amoving charge A charge moving perpendicular to a magnetic fieldmoves in a circular orbit. A charge moving at an angle to a magnetic fieldmoves in a spiral.© iTutor. 2000-2013. All Rights Reserved
  23. 23. Magnetic field near a wireThe field of a straight wire is proportional to thecurrent in the wire and inversely proportional to theradius from the wire.Magnetic field(T)Radius (m)Current (amps)B = 2x10-7 Ir© iTutor. 2000-2013. All Rights Reserved
  24. 24. Magnetic fields in a coilThe magnetic field at the center of a coil comes fromthe whole circumference of the coil.Magneticfield(T)Radiusof coil (m)Current(amps)No. of turns ofwireB = 2 x10-7 NIr© iTutor. 2000-2013. All Rights Reserved
  25. 25. Electromagnets and theElectric Motor Electromagnets are magnetsthat are created when electriccurrent flows in a coil of wire. A simple electromagnet is acoil of wire wrapped around arod of iron or steel. Because iron is magnetic, itconcentrates and amplifiesthe magnetic field created bythe current in the coil.© iTutor. 2000-2013. All Rights Reserved
  26. 26. Electromagnets and theElectric MotorThe right-hand rule: When your fingers curl inthe direction of current,your thumb pointstoward the magnet’snorth pole.© iTutor. 2000-2013. All Rights Reserved
  27. 27. The principle of theelectric motor An electric motor uses electromagnets to convertelectrical energy into mechanical energy. The disk is called the rotor because it can rotate. The disk will keep spinning as long as the externalmagnet is reversed every time the next magnet inthe disk passes by. One or more stationary magnets reverse theirpoles to push and pull on a rotating assembly ofmagnets.© iTutor. 2000-2013. All Rights Reserved
  28. 28. Electric Motors If you take apart an electric motor that runs onbatteries, the same three mechanisms arethere; the difference is in the arrangement ofthe electromagnets and permanent magnets.© iTutor. 2000-2013. All Rights Reserved
  29. 29. Electric motors The rotating part of themotor, including theelectromagnets, iscalled the armature. This diagram shows asmall battery-poweredelectric motor andwhat it looks likeinside with one end ofthe motor caseremoved.© iTutor. 2000-2013. All Rights Reserved
  30. 30. Electric motors The permanent magnetsare on the outside, andthey stay fixed in place. The wires from each of thethree coils are attached tothree metal plates at theend of the armature.commutator© iTutor. 2000-2013. All Rights Reserved
  31. 31. Electric Motors As the motor spins, the three plates come intocontact with the positive and negative brushes. Electric current flows through the brushes intothe coils.© iTutor. 2000-2013. All Rights Reserved
  32. 32.  As the motor turns, the plates rotate past the brushes,switching the electromagnets from north to south byreversing the positive and negative connections to thecoils. The turning electromagnets are attracted and repelledby the permanent magnets and the motor turn© iTutor. 2000-2013. All Rights ReservedElectric MotorsCall us for more Information:www.iTutor.com1-855-694-8886Visit

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