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# U9 cn3 circuits

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Introduction to electric circuits including voltage, current and resistance.

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### U9 cn3 circuits

1. 1. Summary of Circuits E. Alexander Burt Potomac School
2. 2. Review: Electric current requires... <ul><li>Charge carriers that can move – usually electrons moving from atom to atom within a conductor
3. 3. A conductor – a path for the current to flow. Usually this is a metal object.
4. 4. A reason for the charge to move. This is provided by an electric field, and the electric field comes from a difference in voltage. </li></ul>
5. 5. Review: A closer look at Voltage <ul><li>When work is done to separate objects that want to be together, potential energy is stored: </li></ul>http://sdsu-physics.org/physics180/physics180B/p180b_images/e_potentialenergy.gif
6. 6. Voltage, part deux <ul><li>The work done = the potential energy
7. 7. Voltage = work / charge
8. 8. V=w/Q
9. 9. Voltage is like height. In order for charge to flow through a conductor, there must be a difference in voltage between one end and the other. </li></ul>
10. 10. Batteries and power supplies <ul><li>Something has to do work to “lift” the charge up to a voltage. </li><ul><li>That work might come from chemical energy in a battery
11. 11. That work might come from the power company (and they will charge us money for it, too) </li></ul><li>In either case, think of them as “escalators of charge” lifting charge up through a height (voltage). </li></ul>
12. 12. Current <ul><li>Just like water current, electrical current is a flow
13. 13. In this case, it's a flow of charge over time. We use the letter I for current.
14. 14. I=q/t
15. 15. The unit for current is the Ampere (or Amp, for short.) One Amp is one Coulomb per second. </li></ul>
16. 16. La piece de resistance! <ul><li>Think of resistance like electrical friction – it takes some of the energy from the flowing charge and dissipates that energy as heat.
17. 17. Resistance creates a voltage drop
18. 18. The unit for resistance is the Ohm, and it is the ratio of the voltage drop to the current:
19. 19. R=V/I </li></ul>
20. 20. (almost) Everything has resistance. <ul><li>Just about any material has resistance </li><ul><li>Conductors have low resistance (but not zero)
21. 21. Insulators have high resistance (but not infinte) </li></ul><li>In general: </li><ul><li>The longer the conductor the higher the resistance
22. 22. The larger the cross-sectional area, the lower the resistance. </li></ul></ul>
23. 23. Bringing it all together: circuits <ul><li>Circuits are circles! In order for charge to flow, at least one complete loop must be created.
24. 24. Circuits must include a battery or power supply to make the charge move
25. 25. There are equal voltage rises and drops, so the total voltage around the loop is zero. </li></ul>
26. 26. Circuit symbols: <ul><li>We draw circuits with lines representing wires.
27. 27. Other components have symbols: </li></ul>http://castlelearning.com/review/reference/phys11.gif
28. 28. A simple circuit <ul><li>Using the circuit symbols, this is a flashlight: </li></ul>http://www.oneillselectronicmuseum.com/anigifs/flashlightanime.gif
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