Chapter 13 Electricity Section 2 Current GoalsObjectives After

Chapter 13: Electricity Section 2: Current

Goals/Objectives • After completing the lesson, students will be able to. . . ▫ Describe how batteries are sources of voltage; ▫ Explain how a potential difference produces a current in a conductor; ▫ Define resistance; ▫ Distinguish between conductors, superconductors, semiconductors, and insulators

Voltage and Currents • Electrical Potential Energy— Potential energy of a charged object due to its position in an electric field.

Potential Difference • Potential Difference—The change in the electrical potential energy per unit charge. ▫ Change in electrical potential charge divided by charge • The SI unit for potential difference is the volt. ▫ Volt equal to one joule per coulomb

Voltage in Terminals of Batteries • Most common batteries are an electric cell. ▫ Converts chemical energy into electrical ▫ One terminal is positive and the other is negative • Cell—A device that is a source of electric current because of a potential difference, or voltage, between the terminal. ▫ Cells can be wet or dry cells �Dry contains a paste-like electrolyte �Wet contains a liquid electrolyte

Voltages Sets Charges in Motion • When charges are accelerated by an electric field to move to a position of lower potential energy, an electric current is produced. • Current—The rate that electric charges move through a conductor. • The SI unit of current is an ampere (AMP). • Conventional current—The current made of positive charges that would have the same effect as the actual motion of charge in the material.

Electrical Resistance • Resistance—The ratio of the voltage across a conductor to the current it carries. • Light bulbs shine differently because they have different amounts of current in them. ▫ The resistance of the filament in a light bulb determines how bright the bulb is. • Resistance is caused by internal friction, which slows the movement of charges through a conducting material.

Calculating Resistance • A conductor’s resistance indicates how much the motion of charges within it is resisted because of collisions. • Resistance = Voltage/Current • R = V/I • The SI unit of resistance is the ohm. • A resistor is a special type of conductor used to control current.

Insulators • Insulators have high resistance to charge movement, so insulating materials are used to prevent electric current from leaking. • Sometimes it is important to provide a pathway for current to leave a charged object. ▫ Grounding �Grounding wire (electrical outlets)