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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
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
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