Electric Current

Electric Current

Electricity Review

• Resistance is a property of matter that affects the flow of electricity. Some substances have more resistance than others.

• Friction can cause electrons to be transferred from one object to another.

• These static electrical charges can build up on an object and be discharged slowly or rapidly

• This is called static electricity

Multiple Choice

True or False
A positively charged object has lost electrons

• True
• False

Multiple Choice

Static electricity is 

• The balance of electrical charge on an object
• The imbalance of electrical charge on an object
• The discharge of electrical charge
• The build up of protons in the nucleus of an atom 

Multiple Choice

What charge does an electron have?

• negative (-)
• positive (+)
• neutral or no charge (0)

Multiple Choice

What charge does a proton have?

• negative (-)
• positive (+)
• neutral or no charge (0)

Electricity is Related to Magnetism

• Magnetic Fields can produce electrical current in conductors

• Electricity can produce a magnetic field and cause iron and steel objects to act like magnets

• Electromagnets are temporary magnets that lose their magnetism when the electric current is removed

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Electric Current

• When Electric charges are made to flow through a material, they produce an electric current

• An electric current is the continuous flow of electric charges through a material

• The amount of charge that passes through a wire at a given period of time is the rate of electric current

• The unit for the rate of electric current is the Ampere (A)

Multiple Choice

Resistance is...

• What "slows down" electrons
• What "speeds up" electrons
• Moving electrons
• What "pushes" electrons

Multiple Choice

Current is...

• moving protons
• moving electrons
• measured in volts
• measured in ohms

Current in a Circuit

• The electric currents that power your computer need very specific paths to work.

• In order to maintain an electric current, charges must be able to flow continuously in a loop

• An electric circuit is a complete, unbroken path that charges can flow through

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Multiple Choice

What is a circuit?

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

Multiple Choice

this circuit is .....?

• open
• parallel
• closed
• The cutest little circuit evah!

What Affects Current Flow?

• Imagine you are on a water slide at an amusement park. You climb the steps, sit down, and whoosh! The water current carries you down the slide.

• Electric charges flow in much the same way water moves down the slide

• Current flow is affected by the energy of the charges and the properties of the objects that the charges flow through

Electric Currents

• Electric currents flow through wires like water through pipes

• Charges flow because of differences in electric potential energy

• Potential energy from an energy source (like a battery) gets converted into different forms of energy

• If a circuit contains a light bulb, its potential energy is converted into light and heat.

Voltage

• Voltage is the difference in electric potential energy per charge between two points in a circuit

• The energy difference causes charges to flow

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Multiple Choice

The difference in electrical potential energy per charge between two points in a circuit

• Insulator

• Resistance

• Voltage

Multiple Choice

Charges flow through wires because of differences in electrical

• Kinetic Energy

• Potential Energy

Conductors

• Charges can flow more easily through some materials than others.

• A conductor is a material that charge can move through easily.

• Electrons can move freely, allowing conductors to be charged by induction.

• Metals such as copper are good conductors

Multiple Choice

Which of the following is NOT an insulator?

• Wool
• Plastic
• Copper
• Styrofoam

Multiple Choice

Is iron a conductor or insulator?

• Conductor
• Insulator

Insulators

• Wires such as copper wires, are surrounded by insulators

• Insulators are materials, such as rubber, that do not allow charges to flow

• However, electrons can move around within their own atoms (causing polarization)

• Electrons can be stripped off when charging by friction

Semiconductors

• Materials that behave sometimes as conductors and sometimes as insulators

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• 
  

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Conductors vs. Insulators

• The difference between conductors and insulators comes from how strongly electrons are attached to atoms

• The atoms in conductors have loosely bound electrons that can move freely

• Electrons in insulators cannot move freely among atoms

Multiple Choice

A material that prevents heat or an electric current from flowing

• Conductor

• Insulator

• Magnetism

• Electric Circuit

Multiple Choice

Which of the following is an insulator?

• Penny

• Iron

• Tire

• Paperclip

Multiple Choice

Which of the following is a conductor?

• Paper clip

• Chips

• Styrofoam

• Straw

Resistance

• Resistance is the measure of how difficult it is for charges to flow through an object

• The greater the resistance, the less current there is for a given voltage

• The unit of measure of resistance is the ohm

Factors that determine Resistance

• Diameter

• Length

• Material

• Temperature

Diameter and Resistance

• What is easier for you? Slurping a milkshake using a thicker or thinner straw?

• This same idea affects resistance.

• Current flows more easily through a wide wire than a narrow wire

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Length and Resistance

• It would also be easier to drink your milkshake with a short straw vs. a long one

• Similarly, shorter lengths have less resistance

• The longer the object is, the greater its resistance

Material and Resistance

• Some materials have electrons that are held tightly to their atoms

• They have a high resistance because it is difficult for charges to move

• Conductors have less resistance than insulators for this reason

Temperature and Resistance

• Electrical resistance of most materials increases as temperature increases

• 
  

• 
  

Multiple Choice

Material through which charge can easily flow

• Electric Current

• Conductor

• Electric Circuit

• Insulator

Multiple Choice

The measure of how difficult it is for charges to flow through a material

• Voltage

• Conductor

• Resistance

• Insulator

Multiple Choice

The continuous flow of electric charges through a material

• Electric circuit

• Electric Current

• Resistance

• Conductor

Multiple Choice

Which of the following does NOT determine the resistance of a wire?

• Temperature

• Diameter

• Length

• Color

Multiple Choice

All electrical devices contain electric

• acid

• gears

• circuits

• motors

Multiple Choice

Potential electric current can be converted into

• Heat

• Matter

• Waste

• Food