DC Current - The WikiPremed MCAT Course

Electrostatics is the field describing the behavior of charges interacting through the electric force, the force described by Coulomb's Law, which, unlike magnetic force, may occur between stationary charges. We can describe the force between two charges, Charge X and Charge Y, or we might choose to describe the electric field permeating the space surrounding Charge X alone. The electric field of Charge X describes its ability to exert force on any other charge in its vicinity. The electric field tells us how many Newtons of force would be exerted per Coulomb of charge were charge placed at the particular location of the field under discussion. So, with regard to point charges, the description of force applies to a specific interaction between two or more charges while the field describes the ability of one charge to exert force, an ability that permeates the space around it.

An analogy to this relationship between electric force and electric field extends to the relationship between potential energy and electric potential or voltage. We can describe either the specific electrical potential energy state existing between Charge X and Charge Y or we can describe the energy properties of the field of Charge X alone. If we are talking about electric potential or voltage, we ask how hard would it be to do work against this field if we were to move a hypothetical charge from one position to another in the field? How many joules of work does it take to move a Coulomb of hypothetical charge (joules/Coulomb = Volts) from infinitely far away to Point A near Charge X. This is the electric potential of Point A. The joules per Coulomb required to move from Point A to Point B gives the potential difference, or voltage, between these points. So the description of potential energy applies to a specific arrangement of two or more charges while the voltage describes the ability of the field to perform work on hypothetical charges we imagine moving around in a field.

Must know for the MCAT
Direct current	Direct current is the constant flow of electric charge.
Electric current	Electric current is the flow of electric charge.
Ohm's law	Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference across the two points, and inversely proportional to the resistance between them.
Electrical conductor	Conductors, such as copper or aluminum, are materials with atoms having loosely held valence electrons.
Voltage drop	Voltage drop is the reduction in voltage in an electrical circuit between the source and load.
Voltage source	A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary potential from a primary source of the electromotive force.
Ampere	The ampere is the SI unit of electric current.
Kirchhoff's circuit laws	Kirchhoff's circuit laws are a pair of laws that deal with the conservation of charge and energy in electrical circuits.
Electrical conduction	Conduction is the movement of electrically charged particles through a transmission medium which can form an electric current in response to an electric field.
Electrical conductivity	Electrical or specific conductivity is a measure of a material's ability to conduct an electric current.
Resistivity	Electrical resistivity is a measure of how strongly a type of material opposes the flow of electric current.
Voltmeter	A voltmeter is a very high resistance ammeter used for measuring the electrical potential difference between two points in an electric circuit.
Ohmmeter	An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to the flow of an electric current.
Semiconductor	A semiconductor is a solid that has electrical conductivity in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically.
Should know for the MCAT
Free electron model	In solid-state physics, the free electron model is a simple model for the behaviour of valence electrons in a crystal structure of a metallic solid.
Current source	A current source is an electrical or electronic device that delivers or absorbs flow of electric charge.
Wheatstone bridge	A Wheatstone bridge is a device used to measure an unknown electrical resistance which works by balancing two legs of a bridge circuit, one leg of which includes the unknown component.
Superconductivity	Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field.
Bridge circuit	A bridge circuit is a type of electrical circuit in which the current in a conductor splits into two parallel paths and then recombines into a single conductor, thereby enclosing a loop.
Current density	Current density is a vector whose magnitude is the electric current per cross-sectional area measured in the SI system as amperes per square meter.
Siemens	The siemens is the SI derived unit of electric conductance.
Potentiometer	A potentiometer is a variable resistor that can be used as a voltage divider.
May appear in context in MCAT passages - advanced terminology
Drift velocity	The drift velocity is the average velocity, not speed, that a particle, such as an electron, attains due to an electric field.
Voltage divider	A voltage divider is a simple device designed to create a voltage which is proportional to another voltage.
Electronic band structure	The electronic band structure of a solid describes ranges of energy that an electron is forbidden or allowed to have.
N-type semiconductor	An N-type semiconductor is obtained by carrying out a process of doping with valence-five elements to a valence-four semiconductor in order to increase the number of free, negative charge carriers.
P-type semiconductor	A P-type semiconductor is obtained by carrying out a process of doping the semiconductor to increase the number of free, positive charge carriers.
Exciton	An exciton is a bound state of an electron and an imaginary particle called an electron hole in an insulator or semiconductor.

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Must know for the MCAT

Should know for the MCAT

May appear in context in MCAT passages - advanced terminology