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ElectroMagnetism Quick Review

Key Physics Terms

  • Charge:  A fundamental intrinsic property of matter that gives rise to the attractions and repulsions between electrons and protons.
  • Electron: A small, light negative particle in the shell of an atom.
  • Current: Electrical charge flow past a given point per unit of time. 
  • Magnetic Field Lines:  Lines showing the shape and exent of a magnetic field around a permanent magnet or a moving charged object.
  • Magnetic Flux: A measurement of the number of magnetic field lines passing through a particular area or surface.
  • Faraday’s Law: The voltage induced is directly proportionoal to the number of loops and the change in the magnetic flux.  It is inversely proportional to the time that this change occurs throughout.
  • Electromotive Force, EMF:  A voltage that gives rise to a current flow.  This voltage can be induced or created by a changing magnetic field.
  • Induced current:  The flow of charge in a conductor due to the changing magnetic flux near that conductor.
  • Lenz’s Law: The induced emf always gives rise to a current whose magnetic flux opposed the original change in magnetic flux.  Thus, the induced current tries to maintain the level of magnetic flux.
  • Generator:  A machine that produces electricity by a rotating coil of wire immersed in a stationary magnetic field.  This rotating motion could be obtained from a variety of sources.
  • Right Hand Rule:  The fingers extend or curl in the direction of the magnetic field.  The outstretched thumb points in the direction of conventional current.

Key Formulas and Constants

  • FB=BAcosθ
  • Acircle=∏r2
  • ε=-NΔF/Δt
  • ε=BLv
  • v=d/t

Variables Used

  • I=current
  • FB=magnetic flux
  • ΔF=change in magnetic flux over a period of time
  • A=area of surface or loop through which flux flows
  • B=Magentic field strength
  • θ = angle between a normal to the surface, and the B field
  • ε=induced electromotive force, emf
  • N= number of coils of conductor
  • Δt=change in time through which B field changes
  • v=velocity of a conductor moving in a B field
  • L=length of conductor in B field

Typical Key Metric Units

  • Current: Amperes, Amps, A
  • Magnetic field: Teslas, T
  • Magnetic flux: Tm2, Webers, Wb
  • Area: meters squared, m2
  • Length: meters, m
  • EMF: volts, V
  • Angle: degrees
  • Distance or radius: meters, m
  • Velocity: meters per second, m/s
  • Time: seconds, s

Electromagnetism Problem Solving Tips

  • These tips will make it easier to solve any physics problems.
  • Thoroughly read the entire problem.
  • Draw a diagram if needed.
  • Identify all given information. 
  • Identify the quantity to be found.
  • Select appropriate formula(s) that incorporate what you know and what you want to find.
  • Be sure to consider the direction of the B field and flux when deciding upon a current direction.
  • Convert units if needed. 
  • Do any mathematical calculations carefully. 

Right Hand Rule Diagrams

Up Arrow: Bf i eld
Right Arrow: current

Examples of Lenz’s Law