Ohm's Law and Electric Circuits

Electric Circuits

Current, Voltage, and Resistance in a circuit are always related in the same way

Ohm's Law

• Georg Ohm found that conductors and most other devices have a constant resistance regardless of the applied voltage

• Ohm's law says that resistance in a circuit is equal to voltage divided by current

• Resistance = V = I × R

• Units for resistance (Ohms); voltage (volts - V), Current is amps (A)

Multiple Choice

What is the unit for Resistance?

• Ohms

• Volts (V)

• amps (A)

Multiple Choice

What is the unit for Current?

• Ohms

• Volts (V)

• amps (A)

Multiple Choice

What is the unit for Voltage?

• Ohms

• Volts (V)

• amps (A)

What is a Circuit Made of?

• Objects that use electricity contain circuits

• All electric circuits have these basic features: devices that run on electrical energy, sources of electrical energy, and conducting wires

Circuit Energy Sources

• Power plants and batteries are examples of energy sources

• These supply the voltage that causes current to flow

• When the energy source is a battery, current flows from the positive end to the negative end

Energy and Electric Circuits

• Energy is always conserved in a circuit (meaning energy does not get used up)

• Instead, energy is transformed into other forms of energy (ex. heat, light, mechanical, and sound energy)

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Electric Circuits and Wires

• Electric circuits are connected by conducting wires. These wires complete the path of the current.

• Wires allow charges to flow from the energy source to the device that runs on electric current...and then back to the energy source

• Often a switch is used to control the current. Opening a switch breaks the circuit, which shuts off the device

Multiple Choice

Electrons need a GOOD PATH made of a ______ for them to flow. 

• Conductor
• Insulator

Multiple Choice

A wire is an example of _____.

• Battery source 
• Energy pathway
• Load
• All of them

Multiple Choice

Gives a constant supply of electrons. 

• Power source
• Load
• Energy Pathway

Multiple Choice

What is a circuit?

• A constant flow of electricity 
• A path that a current can flow along

Multiple Choice

What is a current?

• A constant flow of electricity 
• A path that a current can flow along

Circuit with labels

-Drawings of circuits have symbols to represent the parts

-See the image to the right to see the parts labeled

Series Circuits

• A series circuit has only one path for the current to take

• If one light goes out, the other lights go out as well

• Light bulbs in the circuit will become dimmer as more bulbs are added. This is because the resistance increases.

Parallel Circuits

• Many paths for current to take

• Because there are multiple pathways currents can take, if one bulb goes out, the others remain lit

• Resistance actually decreases by adding extra pathways because you increase pathways for electric current to follow

• So, adding pathways will not change bulb brightness

Multiple Choice

What is one benefits of using a parallel circuit?  

• It gets confusing.
• There are no problems.
• If one goes down, it does not affect the others. 
• Porque es para llelio. 

Multiple Choice

Which best describes a parallel circuit?

• Electricity flows along one pathway.
• The flow of electricity comes from one source. 
• Electricity flows along more than one pathway. 
• The flow of electricity comes from more than one source. 

Multiple Choice

This is the symbol for a _____?

• an AC current source
• a DC current source
• a battery
• a single cell

Multiple Choice

This is the symbol for a _____?

• switch
• light 
• battery
• wires

Multiple Choice

The picture shows an electrical circuit. This circuit is a series circuit because: 

• It has 3 light bulbs.
• The same current flows through all three light bulbs.
• It uses a single battery.
• The electrical current is divided between the three light bulbs.