Fields

• What are magnetic fields represented by?

  Lines of magnetic flux
• How is magnetic flux measured?

  In Webers, Wb
• What does magnetic flux density, B, measure?

  The strength of a magnetic field
• What is the unit of magnetic flux density?

  Teslas, T
• What are the characteristics of magnetic field lines?

  • Run from north to south poles
  • Never cross, touch, or overlap
  • Tend to shorten/straighten
• How are flux density and flux linked mathematically?

  flux = B * A
• What does flux linkage, NФ, represent?

  The product of flux and number of coils
• What is induction in electromagnetism?

  Production of emf with relative motion
• What does Faraday's law state about induced emf?

  It is proportional to the rate of change of flux linkage
• What does Lenz's law state about induced emf?

  It opposes the change that caused it
• How do Faraday's and Lenz's laws combine mathematically?

  emf = -d(NФ) / dt
• What is permeance in magnetic circuits?

  Conductance of flux lines in a magnetic system
• How does air affect magnetic permeability?

  It has low permeability, reducing magnetic field
• What increases the permeance of a magnetic circuit?

  A high cross-sectional area
• What is the purpose of transformers?

  To change voltage and current of electric supply
• How do transformers use electromagnetic induction?

  To convey magnetic field from primary to secondary coil
• What do the transformer equations relate?

  Voltage, turns ratio, and current
• What are eddy currents in transformers?

  Small currents induced in the magnetic core
• How do eddy currents affect transformer efficiency?

  They dissipate power as heat, wasting energy
• How can the effect of eddy currents be reduced?

  By lamination of the iron core
• What happens when a coil rotates in a magnetic field?

  It produces a flux change inducing an emf
• What is the motor effect?

  A force on a current-carrying wire in a magnetic field
• What is the equation for the magnitude of the force in the motor effect?

  F = BIL
• What does the variable F represent in the motor effect equation?

  The force in Newtons, N
• What does the variable B represent in the motor effect equation?

  The magnetic flux density in Teslas, T
• What does the variable I represent in the motor effect equation?

  The current in Amperes, A
• What does the variable L represent in the motor effect equation?

  The length in meters, m
• What happens when a motor starts spinning?

  An induced emf is generated
• What does back emf do in a motor?

  Provides resistance against the catapult force
• What is an electric field?

  A region where a charged particle experiences force
• What equations apply in a uniform electric field?

  E = V/d and E = F/q
• What are equipotentials in an electric field?

  Lines always perpendicular to the field lines
• What does Coulomb's law calculate?

  The electric force on a charge
• What is the equation for Coulomb's law?

  F = kQq/r²
• What does the variable k represent in Coulomb's law?

  The electric force constant
• What does the variable r represent in Coulomb's law?

  The separation of the charges
• What is electric field strength in terms of Coulomb's law?

  E = kQ/r^2
• What is electric potential energy in terms of Coulomb's law?

  E = kQq/r
• What is electric potential in terms of Coulomb's law?

  V = kQ/r
• How do electric fields differ from gravitational fields?

  Electric fields can be attractive or repulsive