Current and Resistance - (Physics 2)

Current

The movements of electric charge

Electric current

The rate at which these charges move through the cross section of the wire

Opposite of the direction of the current

The movement of the negative charges

Electric current equation

I = △Q/△t

SI unit for currents

Ampere (A)

Charge carriers

Positive and negative charges in motion

Conventional current

Defined in terms of the flow of positive charges

Negative charge carriers

Conventional current in the direction opposite of their physical motion

Electrolyte

Electric current is conducted by the physical movements of cations and anions toward oppositely charged electrodes

Why body fluids and salutary are able to conduct electric charge

They contain charged atoms (ions)

Drift velocity

The net velocity of a charge carrier moving in an electric field

Resistance

The opposition presented to electric current by a material or device

Resistance equation

R = △V/I

SI unit for resistance

Ohm (Ω) which is equal to one volt per ampere (V/A)

Ohm’s law

The resistance is constant over a wide range of applied potential differences

(△V/I = constant) or (△V = IR)

Ohmic

Materials that have a constant resistance over a wide range of potential differences

When resistance is constant…

The current is proportional to the potential difference (the resulting graph is a straight line)

Non-ohmic

Materials that do not function according to Ohm’s law

Diode

A common semiconducting device that is non-ohmic

(its resistance is small for currents in one direction and large for currents in the reverse direction)

Resistor

A simple electrical element that provides a specified resistance

(Can be used to control the current in an attached conductor)

Potentiometer (pots for short)

A special type of resistor that has a fixed contact on one end and an adjustable, sliding contact that allows the user to tap off different potential differences