Electric Current and Resistance Chapter 19 Sections 1 & 2

Current Current – The rate at which electric charges move through a given area. Units for current is called, “Amperes”  A  Amps 1 Amp = 1 Coulomb of Charge per Second

Current vs. Voltage Current is the flow of electrons through a conducting material. Voltage is the pressure in the conducting material that pushes the electrons. Voltage can exist without current. Current can not exist with out voltage.

Electrical Current

Batteries Batteries act as pumps that push charge through a conducting material to create a current.  Batteries do no create charge! Turn chemical energy into electrical energy. Electrical energy is consumed when used, not charge.

AC vs. DC Current Direct current is when charges move in only one direction.  Batteries Alternating current is when the terminals of potential difference are constantly changing sign. Hence there is no net motion of the charge.  Charges vibrate back and forth  Power lines

Resistance Resistance – Ratio of the potential difference across a conductor to the current it carries. Units for resistance is an, “Ohm”  Greek Letter Omega “Ω” Example:  R = 34 Ω (34 ohms)

Resisting the Flow or Charge Resistance in the flow of charge can be related to friction of a moving object. The resistance holds back the electrons from flowing freely through the conductor.  Heat is formed as a result.

Applications of Resistors Resistors are used to control the amount of current in a conductor.  They do not change the potential difference (voltage) They are used in mostly all electrical devices from televisions to microchips.

Factors That Affect Resistance Length  The longer the conductor, the more resistance to the flow of charge. Cross-Sectional Area  The smaller the cross-sectional area of the conductor, the more resistance. Material  Some objects allow the flow of charge more easily then others. Iron has more resistance then copper. Temperature  The warmer the conductor, the more resistance

Ohm’s Law

Superconductors Superconductors – A material whose resistance is zero at or below some critical temperature, which varies with each material. By decreasing the temperature of a conductor, the resistance to the flow of charge also decrease.