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