WELCOME BACK MINIONS Put books on the floor. Only note taking material is to be on your desk.
QUICK REVIEW
OBJECTIVES What is Ohm’s 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
OHM’S LAW Ohm’s Law Resistance is equal to the voltage divided by the current Resistance = Voltage ÷ Current Ω = V ÷ A
OHM’S LAW Different ways to figure this out… Remember: Resistance = Ohms (Ω) Voltage = Volts (V) Current = Amps (A) Resistance = Voltage ÷ Current (or) Ω=V÷A Current = Voltage ÷ Resistance (or) A=V÷Ω Voltage = Current ∙ Resistance (or) V=A∙Ω
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∙Ω V= A (Ω) 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 bulb’s resistance? Resistance = Voltage ÷ Current (or) Ω=V÷A Ω = V ÷ A Ω= 4 ÷ 0.5 Ω= 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÷Ω A= V ÷ Ω 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÷Ω 2) V=A∙Ω 3) Ω=V÷A Resistance = Voltage ÷ Current (or) Ω=V÷A
SO FAR… Formula for current: 1) A=V÷Ω 2) V=A∙Ω 3) Ω=V÷A Current = Voltage ÷ Resistance (or) A=V÷Ω
SO FAR… Formula for voltage: 1) A=V÷Ω 2) V=A∙Ω 3) Ω=V÷A Voltage = Current ∙ Resistance (or) V=A∙Ω
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=V∙I
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 Ohm’s 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 (Ω); 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