WELCOME BACK MINIONSPut 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 ÷ CurrentΩ = 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= 1.8• 1.8 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= 12• 12 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) Parallel2) Magnetic3) Series
SO FAR…
• What kind of circuit is this?1) Parallel2) Magnetic3) 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 = 60• 60 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