Electric Current

Electric Current (I) The net movement of electric charges in a single direction ▫Unit - amperes  Symbol – A  Measurement instrument - ammeter

Voltage or Potential Difference (V) The net movement of electric charges that is caused by an electric force on the charges ▫Unit – Volts  Symbol – V  Measurement instrument – voltmeter Determines the current that will flow through a wire

Resistance (R) The tendency for a material to oppose the flow of electrons ▫Unit - ohms  Symbol – Ω

Resistance (R) Depends on the wire’s material, thickness, and length Thick wire offers less resistance than a thin wire Shorter wire offers less resistance than longer wires As resistance of the circuit increases, the flow of current through the circuit decreases.

Ohm’s Law The current in a circuit equals the voltage difference divided by the resistance Current = Voltage / Resistance

Ohm’s Law Current (I) Resistance (R) Voltage (V)

Calculate Voltage Calculate the voltage difference in a circuit with a resistance of 25 ohms if the current in the circuit is 0.5 amperes. ▫V = ? V ▫I = 0.5 A ▫R = 25 Ω ▫ V = IR ▫ V = (0.5 A) (25 Ω) ▫ V = 12.5 V

Calculate Resistance What is the resistance of a lightbulb that draws 0.5 amperes of current when plugged into a 120- V outlet? ▫V = 120 V ▫I = 0.5 A ▫R = ? Ω ▫ R = V / I ▫ R = (120-V) / 0.5 A ▫ R = 240 Ω

Calculate Current How many amperes of current will flow in a circuit if the voltage difference is 9-V and the resistance in the circuit is 3 ohms? ▫V = 9 V ▫I = ? A ▫R = 3 Ω ▫ I = V / R ▫ I = (9 V) / ( 3 Ω) ▫ I = 3 A

Practice Problems 1.What is the current produced by a potential difference of 240 volts through a resistance of 0.2 ohms? 2.What resistance would produce a current of 120 amps from a 6-volt battery? 3.What voltage is necessary to produce a current of 200 amperes through a resistance of ohms? 4.What is the potential difference if a resistance of 25 ohms produces a current of 250 amperes?

Power (P) The rate at which electrical energy is converted to another form of energy Unit: Watts Formula ▫Power = Current x Voltage Difference

Power Current (I) Voltage (V) Power (W)

Calculating Power The current in an electric clothes dryer is 15 A when its plugged into a 240-volt outlet. How much power does the clothes dryer use? ▫V = 240 V ▫I = 15 A ▫P = ? ▫ P=IV ▫ P = (240 V) (15 A) ▫ P = 3,600 W

Calculating Voltage A VCR that is not playing still uses 10.0 W of power. What is the current if the VCR is plugged into a 120 volt electrical outlet? ▫V = 120 V ▫I = ? ▫P = 10 W ▫ I = P/V ▫ I = 10 W / 120 V ▫ I = A

Calculating Voltage A flashlight bulb use a 2.4 W of power when the current in the bulb is 0.8 A. What is the voltage difference? ▫V = ? V ▫I = 0.8 A ▫P = 2.4 W ▫ V = P / I ▫ V = 2.4 W / 0.8 A ▫ V = 3 V

Practice Problems 1.A toaster oven is plugged into an outlet that provides a voltage difference of 120 V. What power does the oven use if the current is 10 A? 2.What is the current into a microwave oven that requires 700 W if the voltage difference is 120 V? 3.What is the voltage difference in a circuit that uses 2420 W of power if 11 A of current flows into the circuit? 4.How much current flows through a 100 W lightbulb that is plugged into a 120 V outlet?

Electric Circuits Circuit – path that electricity follows Parts of a Electric Circuit  Energy source  Lights  Wire  Switch

Types of Electric Circuits Closed Circuit ▫The switch is closed and the electrons make a complete path Open Circuit ▫The switch is open and the path is not complete

Types of Circuits Series The current has only one loop to flow through Used in flashlights and some holiday lights Parallels The current has two or more branches for current to move through Current can flow through both or wither of the branches