WELCOME BACK MINIONS Put books on the floor. Only note taking material is to be on your desk. QUICK REVIEW OBJECTIVES What is Ohms Law? What are the basic features of an electric circuit? How many paths can currents take in series and parallel circuits? How do you calculate electric power and the energy used by an appliance? STARTING OFF Understand electric circuits First understand the relationship between: Current Voltage Resistance OHMS LAW Ohms Law Resistance is equal to the voltage divided by the current Resistance = Voltage Current = V A OHMS LAW Different ways to figure this out Remember: Resistance = Ohms () Voltage = Volts (V) Current = Amps (A) Resistance = Voltage Current (or) =VA Current = Voltage Resistance (or) A=V Voltage = Current Resistance (or) V=A EXAMPLE OF EACH Circuit has a resistance of 30 ohms and a current of.06 amps. How many Volts are there? Voltage = Current Resistance (or) V=A V= A () V=.06 (30) V= volts EXAMPLE OF EACH In a circuit there is a 0.5 Amp current in the bulb. The voltage across the bulb is 4 volts. What is the bulbs resistance? Resistance = Voltage Current (or) =VA = V A = 4 0.5 = 8 8 ohms EXAMPLE OF EACH A waffle iron is running on a voltage of 120 and the resistance is 10 ohms. What is the current? Current = Voltage Resistance (or) A=V A= V A= 120 10 A= amps FEATURES OF A CIRCUIT Three Features Circuits have devices that are run by electrical energy. A circuit has a source of electrical energy. Electric circuits are connected by conducting wires. DIAGRAMMING A CIRCUIT SERIES CIRCUIT In a series circuit, there is only one path for the current to take. SERIES CIRCUIT Disadvantage Break in the circuit from a burned out bulb! Light bulbs are dim as opposed to just one alone. Each bulb is a resistor! PARALLEL CIRCUIT In a parallel circuit, there are several paths for a current to take. PARALLEL CIRCUIT Interesting fact When you add a branch to a parallel circuit the overall resistance decreases. But if a resistance decreases, the current increases. WHAT WILL HAPPEN? Questions about the diagram below SO FAR Formula for resistance: 1) A=V 2) V=A 3) =VA Resistance = Voltage Current (or) =VA SO FAR Formula for current: 1) A=V 2) V=A 3) =VA Current = Voltage Resistance (or) A=V SO FAR Formula for voltage: 1) A=V 2) V=A 3) =VA Voltage = Current Resistance (or) V=A SO FAR What kind of circuit is this? 1) Parallel 2) Magnetic 3) Series SO FAR What kind of circuit is this? 1) Parallel 2) Magnetic 3) Series ELECTRIC POWER Power The rate at which energy is transformed from one form to another. Unit of power is the watt (W). CALCULATING POWER Power = watts (W) Voltage = volts (V) Current = amps (I) The letter i? I = Intensity of the Current Power = Voltage x Current W=VI EXAMPLE A household light bulb has about 0.5 amps of current in it. Since the standard household voltage is 120 volts, what is the power rating for this bulb? Power = Voltage x Current Power = 120 x 0.5 Power = watts or 60W REVIEW What is Ohms Law? 1) Resistance is equal to the voltage divided by the current. 2) An Ohm cannot be created nor destroyed. 3) A current seeks the path of least resistance REVIEW What are the basic features of an electric circuit? 1) Run by electrical energy, has an electrical source, and connected by insulating wires. 2) Run by electrical energy, has an electrical source, and connected by conducting wires. 3) Resistance = Ohms (); Voltage = Volts (V); Current = Amps (A) REVIEW How many paths can currents take in series and parallel circuits? 1) Series provides several paths while parallel is one continuous circuit. 2) Parallel and series are one continuous circuit. 3) Series is one continuous circuit while a parallel provides several paths. REVIEW How do you calculate electric power and the energy used by an appliance? 1) Power = Voltage Current 2) Power = Voltage x Current 3) Power = Current Resistance