Electric Charge Electric Charge & Current Current Electric Charge Current Chapter 20

Types of Electric Charge  What are the two types of charge?  Positive  Negative  Ben Franklin named these charges.  Where do these charges come from?  Protons  Electrons

Interactions Between Charges

Electric Field  Region around a charged particle where a force is exerted.  Similar to magnetic field  Draw with lines to show what kind of force would be on a test charge (always +)  Remember, what is a force?

Electric Fields around Single Charge

Electric Fields Around Multiple Charges

Static Charge  What is the charge of most objects?  Trick question??  Most objects are neutral.  What does that mean?  Protons equal Electrons or + = -

So, how do things become charged?  Can all materials become charged?  Insulators: electrons cannot be lost easily  Conductors: electrons free to move  Electrons can be lost or gained.  Less electrons means…  Less negative or a overall positive charge  More electrons means…  More negative or a overall negative charge

Static Electricity Static Electricity  A buildup of charges on an object is called Static Electricity.  Charges buildup but do not flow.

Transferring Charge 1. Conduction Charge transfer through direct contact 2. Induction Movement of electrons to one part of an object caused by the electric field of another object

Conservation of Charge  Charges (electrons) are not created or destroyed  So, if one object gains electrons another object must have lost electrons  And, if one object loses electrons another object must have gained electrons

Static Cling Why does your sock stick to your shirt? Its all about charges, opposites attract. Why does a dryer sheet help reduce this? When might static cling be beneficial?

Static Discharge  When a negatively charged object and a positively object are brought together, electrons move until both objects have the same charge.  The loss of static electricity as electric charges move off an object is called static discharge.

How can static discharge?  Humidity  Water in the air can pick up charge that has built up on an object.  Sparks  Shock, electrons moving from hand to door knob results in neutral objects again.  Lightning  Electrons buildup on clouds then discharge to areas of positive charge.

Detecting Charge  Electric charge is invisible, but it can be detected by a special instrument called a Electroscope.  Uncharged: metal leaves hang straight  Charged: metal leaves repel

Circuit Measurements

Electrical Potential  An object will move from a place of high potential energy to a place of low potential energy.  What would be an example of this?  Electrons will also move from high potential to low potential energy exerted by an electric field.  Potential energy per unit of charge is called electrical potential.

Voltage  The difference in electrical potential between two places is called the potential difference.  This provides the force that pushes the charge through a circuit.  Voltage is the unit for electrical difference.  Voltage causes current to flow through an electric circuit.

Voltage Sources  Creates a potential difference.  Batteries and generators  Just as an increase in the difference in height causes a greater flow of water, an increase in voltage causes a greater flow of electric current.

Resistance  Opposition to the flow of charge.  Depends on the type of wire, thickness, and length.  Current depends on resistance.  The greater the resistance, the less current there is for a given voltage.  Path of least resistance

Ohm’s Law  Voltmeter: measures potential difference  Ammeter: measures current  Ohm’s Law:V=IR  Voltage=Current x Resistance Volts=Amps x Ohms

Series & Parallel Circuits Series & Parallel Circuits

Series Circuits  Only one path for the current to take  All parts of circuit connected one after the other.  Added resistors (light bulbs) decreases current  Ammeter connected in series.

Parallel Circuit  Several pathways for current to flow  Each resistor connect to energy source separately  Each pathway can have different current going through it  Voltmeter is connected in parallel

Household Circuits  Would you want your house to be series or parallel?  Why?

Electrical Safety

Becoming Part of a Circuit  Short circuit: a connection that allows current to flow through an unintended path  Exposed Wires  Resisting Current

Grounding  Third Prong  Lightning Rods  A lightning rod is connected to a grounding wire. When lightning strikes the rod, charges flow through the rod, into the wire, and then into Earth.

Fuses & Circuit Breakers  In order to prevent circuits from overheating, devices called fuses and circuit breakers are added to circuits.  A fuse is a device that contains a thin strip of metal that will melt if too much current flows through it.  A circuit breaker is a safety device that uses an electromagnet to shut off the circuit when the current gets too high.

Electric Shocks  Current in the body  The severity of an electric shock depends on the current. .1 to.2 amps can be dangerous  Resistance in the body  Dry skin – High resistance  Wet skin – Low resistance