Electricity Chapter 16

Electrical Charge and Force Section 16.1

Introduction Turning the tv on Removing your hand from a hot pan Speaking into the cell phone All of these are carried by electrical pulses

Electric Charge A property of matter that creates electric and magnetic forces and interaction Example: Being shocked opening a metal door Notice the electric charge as a shock

Electric Charge Like charges repel Opposite charges attract Positive Negative Example: Rub 2 balloons on your hair, put them close together they repel So: Hair is positive, the balloons are negative, and both balloons have a negative charge so they repel

Electric Charge Charge of an object depends on imbalance of protons and electrons REVIEW!! (Write if you don’t remember!) Everything is made of atoms Atoms are made of protons, neutrons, and electrons Protons (+), neutrons (neutral), electrons (-) An imbalance causes a net charge

Electric Charge REVIEW (cont’d) More electrons = a negative charged object More protons = a positive charged object SI Unit for electric charge is the Coulomb (C) Net charge is always in multiples of 1.6×10-19

Electric Charge Conductors and Insulators Cords to electrical items are wrapped in rubber or plastic but have metal wires in the center Metal is an electrical conductor (material that charges move freely and carry a current) Plastic is an electrical insulator (material that does not transfer current easily) Protects people from shock, efficient

Electric Charge Objects can be charged by transferring electrons Protons and neutrons are found in nucleus Valence electrons can be transferred Charging by friction Slide into car and electrons from seat go to clothing; seat (+) and clothing is (-) Charging by contact Touching a door knob

Electric Charge Charges move w/in uncharged objects Neutral object may have an end that is housing all the (+) particles and the other end has all the (-) particles, but still neutral

Electric Force Force of attraction or repulsion between objects due to charge Holds atoms together Bonding of atoms Holds proteins together

Electric Force Depend on charge and distance The force between 2 objects is proportional to the product of the charges Increase charge = increase the force Electric force is inversely proportional to the square of the distance of 2 objects Increase distance = decrease in force to ¼ of original value

Electric Force Acts through a field Electric field- a region in space around a charged object that causes a stationary charged object to experience an electric force

Electric Force Field Lines (in reference to a + field) Point out on (+) Point in on (-) Field lines never cross + -

Electric Force Pg 536 Fig 7 Field lines show direction of electric field Relative strength b/c of charge

Current Section 16.2

Voltage and Current REVIEW GPE depends on the objects position (move from high GPE to low GPE) Electric potential energy- the ability to move an electric charge from one point to another Depends on position in electric field

Voltage and Current A (-) charge will move away from another (-) charge

Voltage and Current Potential difference is measured in volts (V) 1 J/C Potential difference- between any 2 points the work that is done against electric forces to move a unit charge from one point to the other; called voltage

Voltage and Current Cell- device that is a source of electric current b/c of a potential difference, or voltage, between the terminals Example: battery- convert chemical energy to electric energy Avg cell has a potential difference of 1.5 V Electrolyte- solution that conducts electricity Electrodes- conducting materials

Voltage and Current Voltage sets a charge into motion Current- the rate that electric charges move through a conductor SI Unit- amphere (A) Direct current- charges move form 1 terminal to the next in the same direction

Voltage and Current Conventional Current is the movement of a positive charge Direction of the current is opposite to the direction that the electrons move

Electrical Resistance Resistance- the opposition posed by a material or a device to the flow of current Changes in current cause different watts of light bulbs to shine different Caused by internal friction Slows the movement of charges through a conducting material

Resistance Resistance can be calculated resistance= voltage/current R=V/I SI unit for resistance is ohm (Ω) Resistor- special type of conductor used to control current

Resistances Conductors have low resistances Basically, metal is not going to slow down the flow of an electric field

Resistance Superconductors- materials that become conductors BELOW a certain temperature (called the critical temperature) They have zero resistance Used in: Filaments High speed express trains Super magnets

Resistance Semiconductors- intermediate between conductors and insulators In pure state- insulators Impurities added to semiconductors cause them to be conductors

Resistance Insulators have high resistance Prevent the free flow of electric charge Grounding- conducting wire ran between the charged object and the ground (safety reason) If a charge is built up, it will be discharged to the Earth safely

Circuits Chapter 16.3

Circuit Introduction Electric circuit is a path through which charges can be conducted Closed circuit- conducting path produced when a light bulb in connected across the terminals Open circuit- no complete path, no charge flow, so no current Voltage source is always part of conducting path

Resistors Lightbulbs Hair dryers Stoves TV Curling Iron

Open circuit Closed circuit

Circuits Switches interrupt the flow of charges in a circuit Switch is used to open or close a circuit Ex: turn light on and off Knife switch (see previous pic) Up=open circuit (no flow) Down=closed circuit (travel through bar)

Circuits Schematic diagrams are used to represent circuits A graphical representation of a circuit that uses lines to represent wires and different symbols to represent components Pg 548 Know table 2 symbols

Series and Parallel Circuits Series circuits have a single path for current Devices hooked into a series will have the same current to pass in all of them However resistance maybe different Therefore voltage in each device in a series circuit can be different

Series and Parallel Circuits Parallel circuits have multiple paths Circuit in which all of the components are connected to each other side by side Current in each device doesn’t have to be the same Sum of all the device currents=total current Different resistances and different voltages

Parallel Circuit

Electric Power and Electrical Energy Electrical energy- the energy that is associated w/charged particles b/c of their positions Electric power is the rate at which electrical energy is used (for work) in a circuit Electric power=current × voltage P=IV SI unit of power is Watts (W)

Electric Power and Energy The power that is lost or “dissipated” by a resistor can be found P=I2R=V2/R Power bills are determined by measuring kilowatt-hours

Fuses and Circuit Breakers When too much current is moving through a circuit, the resistance is lowered, and this is now unsafe This is known as overloading which can cause a fire Short circuit- when a an alternative pathway for current is created b/c a wire’s insulation breaks down

Fuses and Circuit Breakers Fuses melt to prevent circuit overload Fuses- metal ribbon w/low melting point, that melts when current becomes to great “Blown fuse”- 20A fuse blows when the current exceeds 20A Warning

Fuses and Circuit Breakers Circuit breakers open circuits with high current When a circuit overloads the circuit breaker opens the circuit Can reset breakers, unlike fuses