Praxis II physics (5265) Part 2: Electricity and Magnetism
Insulator
Don't allow electricity to flow through it easily. non-metallic solids are said to be good examples.
Potential difference
Work per unit charge required to move a charge between the points. V=work/charge
Inductor
A coil which stores energy in the magnetic field. Combines like resistors in when in parallel and when in series.
Photocell
A device that converts light energy into electrical energy.
Transformer
A device that increases or decreases the voltage of alternating current.
Voltmeter
A device that measures potential differences in volts and is placed in parallel across a part of the circuit.
Battery
A device used to convert chemical energy into electric energy. A group of voltaic cells connected together in a series or parallel connection.
Generator
A device used to convert mechanical energy into electrical energy.
Ammeter
A device used to measure current by placing it in series with the circuit.
Electric charge
A fundamental property of matter that can be either positive or negative
Bar magnet
A magnet in the form of a bar with magnetic poles at each end.
Permanent magnet
A magnet made of material that keeps its magnetism.
Superconductor
A material that has almost zero resistance when it is cooled to low temperatures.
Resistance
A material's opposition to the flow of electric current.
Magnetic field
A region surrounding a magnet in which ferrous materials or charged particles experience a force.
Conductor
Allows the flow of electrons. Metals such as copper is said to be a good one.
Alternating Current
An electric current that changes it's magnitude and direction according to a regular frequency
Capacitor
An electrical device used to store electrical charge. When in parallel combines like resistors in series, and when in series combines like resitors in parallel.
Energy
Capacity to do work. Power x time.
Direct Current
Electric current that is moving through an electrical circuit in one direction only.
Semiconductor
Elements that conduct an electric current under certain conditions.
Electric potential energy
Energy a charge has due to its location in an electric field., U=kq₁q₂/r or U=Eqd
Electromotive force (EMF)
Energy gained by an electron when it is accelerated through a potential difference of 1 volt, given by qV where q is 1.6 x 10⁻¹⁹ C and V is 1 volt.
Ampere's Law
For any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed in the loop.∑B(‖) ∆L = µ₀I
Electrostatic force
Force between electrically charged objects.
Electric field
Force that a source charge would exert on a positive test charge q₀ within its proximity divided by that test charge; E = F/q₀
Resistivity
Intrinsic property of a conductor denoted by ρ used to measure its resistance in the equation R = ρ L/A. L = length of the conductor, A = cross-sectional area.
Coulomb's law
Inverse square law, Electric Force = F = k * (q₁q₂)/r² = 1/(4πε₀) * (q₁q₂)/r
Electromagnet
Made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops.
Capacitance
Measure of a capacitor's ability to store charge, calculated by the ratio of the magnitude of charge on one plate to the voltage across the two plates, expressed in SI units, farads.
Lodestones
Naturally occuring rocks that can attract metal objects. Can be used to magnetize metal objects.
Electric flux
Product of a surface area and the component of the electric field perpendicular to the surface, Φ=E*A
Inductance
Property of a conductor in which a change on the current flowing though it creates an EMF in the conductor.
Joule's Law
Rate of heat production is directly proportional to the resistance of the circuit and to the square of the current. H=I ²Rt = VIt H-heat, I-Current, V-voltage, t-time.
Power
Ratio of the work done to the time needed to do the work.
Biot-Savart law
Relates a magnetc field to the magnitude, direction, length, and proximity of the electric current. dB = (µ₀ I dI x r^ ) / 4πr² where r^ is the unit vector pointing in the directin of r.
Induced charge
Static charge caused by the presence of an already charged object
Metal permeability
The ability of a metal to be magnetized. Substances such as iron, colbalt, and nickel have among the highest.
Electric current
The continuous flow of electric charges through a material.
Kirchoff's current law
The current that goes into a branch is equal to the current that comes out of a branch.
Gauss's law
The electric flux through a closed surface depends upon the charge enclosed in that surface., Φ=q/ε₀
Motional EMF
The emf produced across a conductor due to its motion through a magnetic field
Lenz's Law
The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant.
Right-hand rule
The thumb is pointed in the direction of the current, your fingers in the direction of the magnetic field. your open palm is the direction of the force.
Kirchoff's voltage law
The total of all voltage drops must add upp to the voltage that is supplied in the battery.
Faraday's Law of Induction
The voltage induced in a coil is directly proportional to the rate of change of the magnetic field through the coil. , V= -N(Δ(BA)/Δt)
Motor
Uses magnets to convert electrical energy into mechanical energy.
Ohm's law
V= IR. ,The direct current flowing in an electric circuit is directly proportional to the voltage applied to the circuit.
Electric potential
Work needed to move test charge. In an electric field, it is the work done per unit charge q to bring that charge from infinity to point P. Units are J/Coulomb
Magnetic flux
the lines of force surrounding a permanent magnet or a moving charged particle
