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Electricity

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.

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Electricity

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Presentation Transcript

  1. Electricity Chapter 16

  2. Electrical Charge and Force Section 16.1

  3. 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

  4. 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

  5. Electric Charge • Like charges repel • Opposite charges attract • Positive • Negative

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

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

  12. 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

  13. 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

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

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

  16. Current Section 16.2

  17. 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

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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

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

  26. 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

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

  28. 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

  29. Circuits Chapter 16.3

  30. 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

  31. Resistors • Lightbulbs • Hair dryers • Stoves • TV • Curling Iron

  32. Open circuit Closed circuit

  33. 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)

  34. 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

  35. 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

  36. 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

  37. Parallel Circuit

  38. 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)

  39. 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

  40. 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

  41. 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

  42. 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

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