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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    Examples of Lenz’s Law 