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Electricity

Electricity. Chapter 7. Positive and Negative Charges. Protons = positive charge Electrons = negative charge Most atoms have the same number of protons and electrons and thus will have no net charge. Atoms become charged when they gain or lose electrons. Static Electricity.

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Electricity

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  1. Electricity Chapter 7

  2. Positive and Negative Charges • Protons = positive charge • Electrons = negative charge • Most atoms have the same number of protons and electrons and thus will have no net charge. • Atoms become charged when they gain or lose electrons.

  3. Static Electricity • The accumulation of excess electric charges on an object

  4. Electricity obeys rules??? • Law of conservation of charges - Charges can be transferred from object to object, but cannot be created or destroyed. • Opposite charges attract, like charges repel. • electrons move easier through conductors • ex. metals • Electrons do not move easy through insulators • ex. plastic, wood, rubber, and glass

  5. Transferring Electric Charge • Charging by contact • process of transferring charge by touching or rubbing • Ex. Static electricity from rubbing your feet on carpet • Charge by induction • the rearrangement of electrons on a neutral object caused by a nearby charged object • Ex. a negatively charged balloon near your sleeve causes an area of your sleeve to become positively charged

  6. Transferring Electric Charge • Static discharge • A transfer of charge through the air b/w two objects because of a buildup of static electricity • Ex. Lightning

  7. Read Page 197 Write and Answer the following questions • When the warm humid air rises to meet the cold air, what causes the air masses to churn together? • What electric property causes the negative charges in the cloud to be attracted to the positive charges in the ground? • Why does the ground below a cloud have a concentration of positive charges?

  8. Electric current Chapter 7 Sec 2

  9. Electric current • The flow of charges through a conductor (like a wire) is called electric current. • Usually the flow of electrons • Measured in Amperes (A) • Flow from high to low voltage. • A voltage difference is the push that causes charges to move. • Voltage difference is measured in volts (V).

  10. Circuit • For charges to flow, the wire or conductor must always be connected in a closed path called a circuit.

  11. Sources of Electricity • Dry Cell Battery • Wet Cell Battery • Wall Socket

  12. Sources of Electricity • Dry cell battery - produces voltage difference b/w its zinc container and its carbon suspension rod, causing current to flow b/w them • Wet cell battery – contains two connected plates made of different metals in a conducting solution. • Wall sockets – have a voltage difference across the two holes of an electrical outlet, and a generator at a power plant provides this voltage difference

  13. Resistance • The tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light. • All materials have some electrical resistance. • Measured in ohms (Ω) • Making wires thinner, longer, or hotter increases the resistance.

  14. Ohms Law current (in amperes) = voltage difference (in volts) resistance (in ohms) I = V/R

  15. Ohms Law Example Problem #1: What is the current in a 30V circuit if the resistance is 6Ω? current (in amperes) = voltage difference (in volts) resistance (in ohms) I = ? V = 30V R = 6Ω

  16. Ohms Law Example Problem #2: An Ipod uses a standard 3.7 V battery. How much resistance is in the circuit if it uses a current of 0.025 A? current (in amperes) = voltage difference (in volts) resistance (in ohms) I = V/R

  17. Electrical circuits Chapter 7 Section 3

  18. Series Circuit • Series circuit - The current only has one loop to flow through • Parts of the circuit are wired one after another, so the amount of current is the same through every part • Ex. String of holiday lights

  19. Parallel Circuit • Parallel circuit – contains two or more branches for current to move through • Parts can be turned off without affecting the entire circuit • Ex. the electrical system in a house

  20. Household Circuits • Parallel circuits connected in a logical network. • Electric energy enters your home at the circuit breaker or fuse box and branches out to wall sockets, lights, and major appliances • Guards against overheating • Electric fuse • Circuit breaker

  21. Electrical Energy • Electrical energy is easily converted to thermal, radiant or mechanical energy. • Electrical power – the rate at which electrical energy is converted to another form of energy • Electrical power is expressed in watts (W). • Power = current X voltage difference • P(watts) = I (amperes) X V (volts)

  22. Example Problem • Your microwave runs at a current of 10 amps. A standard plug in your house has a voltage difference of 120 volts. How much electrical power does it take to run this appliance? P = I x V

  23. Example problem 2 • If it takes 1750 watts of power to run my hairdryer, and we know that it is plugged up to 120 volt outlet what must be the current? P = I x V

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