Electromagnitism

• Electric charge


  An electrical property of matter that creates electric and magnetic forces and interactions
• Electric charge


  • Like charges repel, and opposite charges attract
  • The two types of charges are called positive and negative
• Electric charge of an object


  Depends on the imbalance of its protons and electrons
• Electrons, protons, neutrons


  • Electrons are negatively charged, protons are positively charged, and neutrons are neutral (no charge)
• Negatively charged objects


  Have more electrons than protons
• Positively charged objects


  Have fewer electrons than protons
• SI unit of electric charge

  Coulomb, C
• A proton has a charge of 1.6 x 10-19 C
• An electron has a charge of 1.6 x 10-19 C
• The net electric charge of a charged object is always a multiple of 1.6 x 10-19 C
• Transfer of charges


  • Occurs when two objects come close to each other
• Charging by friction


  A material gains electrons and becomes negatively charged, and the other loses electrons and becomes positively charged
• Charging without friction


  Touching a neutral object with a charged object (charged by contact)
• Charges move within uniform objects
• Although the total charge of a conductor will be zero, the sides will have an induced charge
• Polarization of the atomic molecules of an insulator produces induced charge on the surface of the insulator
• Force between charges


  • Opposite charges attract, like charges repel
  • Force is along the line joining the particles
• Electrostatic force


  F = k Q₁Q₂/r²
• Gravitational force


  F = G M₁M₂/r²
• Electrostatic force is much stronger than gravitational force
• Electric field


  Field lines show both the direction of the field and the relative strength due to the charge
• Magnetic dipole


  • Has a north pole and a south pole
• There are no magnetic 'charges'</b>
• Magnetic field


  • Field lines indicate direction of force, density indicates strength of force
• The Earth is a magnet with a north and south magnetic pole
• Compass


  A magnet that aligns with the Earth's magnetic field
• Work


  Force x Distance
• Electrostatic potential (voltage)


  Potential energy per unit charge, measured in Volts
• Battery


  A device that is a source of electric potential difference (voltage) due to a chemical reaction
• Electric current


  The rate of flow of electric charge, measured in Amperes
• Direct current (DC)


  • Charges always move in the same direction
• Alternating current (AC)


  • Charges change direction periodically
• Moving electric charges and magnets produce interesting behaviors
• James Clerk Maxwell published mathematical theory relating electricity and magnetism

  1865
• Magnetic field


  Produced by electric current in a wire
• Solenoid


  A sequence of current loops that can produce a strong magnetic field, an electromagnet
• Magnetic field in a permanent magnet arises from microscopic circulating currents, primarily from spinning electrons
• Magnetic force


  Force on a moving charge in a magnetic field, perpendicular to both the velocity and the magnetic field
• Faraday's law of induction


  A changing magnetic field causes an electric current in a metal
• Lenz's law


  The current produced by a changing magnetic field opposes the change in the magnetic field