Learning Objectives I can describe electric current and how voltage is applied to that current. I can compare direct current to alternating current and describe some devices that use each current. I can describe factors that create resistance and its relationship with electric current.

Ohio New Learning Standards for Science Ohio 7th Grade, Physical Science #3 (7.SIA.3) – Energy can be transferred through a variety of ways.

Lesson Opener

Unit 8, Lesson 5 – Electric Current What is an electric current? - using a smartphone, iPad, iPod, laptop, flat screen, or e-reader depends upon moving electrical charges, called electrical energy, to power them - electrical charges flow through wires in those devices & that rate of electrical charge flow is called electric current

Unit 8, Lesson 5 – Electric Current How is electric current measured? - electric current is the amount of electron charge that passes a location in a wire every second

Unit 8, Lesson 5 – Electric Current - electric current is measured in units called amperes, or amps (A) - a wire with a current of 2A has twice as much charge passing by each second as a wire with a current of 1A

Unit 8, Lesson 5 – Electric Current What are two kinds of current? - two kinds of electric current are direct current (DC) and alternating current (AC); both carry electrical charges, but they differ in how the charges move

Unit 8, Lesson 5 – Electric Current Complete #7, pg.591

Unit 8, Lesson 5 – Electric Current What affects electric current? - two factors that can affect the current in a wire are voltage and resistance - voltage is the amount of work required to move each unit of charge between two points - higher voltage produces a higher rate of flow of electric charges in a given wire

Unit 8, Lesson 5 – Electric Current - voltage is expressed in units of volts (V) - voltage is sometimes called “electric potential” because it’s a measure of the electrical potential energy per unit charge! Complete #7, pg.592

Unit 8, Lesson 5 – Electric Current

Unit 8, Lesson 5 – Electric Current - some materials do not allow electric charges to move freely - the opposition to the flow of electric charge is called resistance and is expressed in ohms (), the Greek letter for omega - higher resistance at the same voltage results in lower current!

Unit 8, Lesson 5 – Electric Current What affects electrical resistance? - a material’s composition affects its resistance (silver & copper have low resistance, whereas iron & nickel have high resistance) - electrical insulators such as plastic have such high resistance that electric charges cannot flow in them at all (this is why most wires are coated in plastic!)

Unit 8, Lesson 5 – Electric Current - other factors that affect the resistance of a wire are thickness, length, and temperature - a thin wire has higher resistance than a thicker wire - a long wire has higher resistance than a shorter wire - a hot wire has higher resistance than a cooler wire Complete #10, pg.593

Unit 8, Lesson 5 – Electric Current

Visual Summary

Exit Question What happens to the electric current in a wire as voltage is increased?