Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.



Published on

Published in: Education, Technology, Business
  • Be the first to comment


  1. 1. Circuits March 30th, 2009
  2. 2. Electric Circuits <ul><li>A circuit is simply a closed loop through which charges can continuously move. </li></ul><ul><li>The word circuit is from </li></ul><ul><li>the same base as the </li></ul><ul><li>word circle, which </li></ul><ul><li>describes how the electrons move </li></ul>
  3. 3. Requirements of a Circuit <ul><li>There must be an energy supply capable doing work on charge to move it from a low potential energy to a high potential energy location. This establishes a potential difference (voltage) across the two ends of the external circuit. </li></ul><ul><li>There must be a closed </li></ul><ul><li>conducting loop in the circuit </li></ul><ul><li>which stretches from the </li></ul><ul><li>high potential, positive terminal </li></ul><ul><li>to the low potential, negative terminal. </li></ul>
  4. 4. An analogy to help you… <ul><li>A circuit is like a rollercoaster </li></ul><ul><ul><li>It is a complete loop </li></ul></ul><ul><ul><li>There is a place where energy is put in to increase potential energy (a battery in a circuit and the chain pulling up the hill in the rollercoaster) </li></ul></ul><ul><ul><li>The rollercoaster naturally flows downhill just like charge in a circuit naturally flows from high potential to low potential </li></ul></ul>
  5. 5. <ul><li>The diagram at the right shows a light bulb connected to a 12-V car battery. The + and - terminals are shown. </li></ul><ul><ul><li>As a + charge moves through the battery </li></ul></ul><ul><ul><li>from D to A, it ________ (gains, loses) electric potential. </li></ul></ul><ul><ul><li>As a + charge moves through the external </li></ul></ul><ul><ul><li>circuit from A to D, ________ (gains, loses) </li></ul></ul><ul><ul><li>electric potential. </li></ul></ul><ul><li>Use >, <, and = signs to compare the electric potential (V) at the four points of the circuit. </li></ul><ul><ul><li>VA ___ VB ____ VC ____ VD </li></ul></ul>
  6. 6. Decide if each statement is true or false: <ul><li>When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again. </li></ul><ul><li>2. An electrochemical cell can be a source of charge in a circuit. The charge which flows through the circuit originates in the cell. </li></ul><ul><li>3. Charge becomes used up as it flows through a circuit. The amount of charge which exits a light bulb is less than the amount which enters the light bulb. </li></ul><ul><li>4. The local electrical utility company supplies millions and millions of electrons to our homes everyday. </li></ul>
  7. 7. All statements were FALSE!! <ul><li>When a battery is “dead” it is out of energy required to push a charge from one terminal to another </li></ul><ul><ul><li>This energy can be restored in some batteries with a reversible chemical reaction…so it is more like reenergizing than recharging your batteries </li></ul></ul><ul><li>Batteries are the source of energy in a circuit, charges carry the energy </li></ul><ul><li>Charge is not used up in a circuit, energy is </li></ul><ul><li>Electrons are already in your home, the power company supplies the energy to these electrons </li></ul>
  8. 8. Circuits <ul><li>A circuit is a set of electrical components connected so they provide one or more complete paths for the movement of charges </li></ul><ul><li>A load is any component or group of components that dissipates energy </li></ul><ul><li>A simple circuit consists of a source of potential difference (electrical energy) and a load </li></ul>
  9. 9. Drawing Circuits with Schematic Diagrams <ul><li>Graphic representation </li></ul><ul><li>of an electric circuit </li></ul><ul><li>Uses standardized </li></ul><ul><li>symbols representing </li></ul><ul><li>circuit components </li></ul><ul><li>COPY DOWN </li></ul><ul><li>SYMBOLS FROM </li></ul><ul><li>OVERHEAD </li></ul>
  10. 10. Light Bulbs <ul><li>A light bulb contains </li></ul><ul><li>a complete conducting path </li></ul><ul><ul><li>See Overhead </li></ul></ul><ul><ul><ul><li>(regular and decorative lights) </li></ul></ul></ul><ul><li>A light bulb is considered </li></ul><ul><li>a load because it dissipates </li></ul><ul><li>electrical energy (by </li></ul><ul><li>converting it to light energy) </li></ul>
  11. 11. EMF <ul><li>Electromotive Force </li></ul><ul><ul><li>The energy per unit charge supplied by a source of electric current </li></ul></ul><ul><ul><li>Any device that increases the potential difference and energy of charges circulating in a circuit </li></ul></ul><ul><ul><li>Current flow shows </li></ul></ul><ul><ul><li>the direction of + </li></ul></ul><ul><ul><li>charges </li></ul></ul><ul><ul><li>EMF shows the flow </li></ul></ul><ul><ul><li>of electrons </li></ul></ul>
  12. 12. Types of Circuits <ul><li>Closed circuit </li></ul><ul><ul><li>Path from one terminal to the other is complete. A potential difference exists and electrons move from one terminal to the other. </li></ul></ul><ul><li>Open Circuit </li></ul><ul><ul><li>No complete path. No charge flow and no current </li></ul></ul><ul><li>Short Circuits </li></ul><ul><ul><li>Without a load the circuit contains little resistance to the movement of charges. </li></ul></ul><ul><ul><li>This causes high current which can damage circuit components. </li></ul></ul>
  13. 13. Types of Circuits <ul><li>Series Circuit </li></ul><ul><ul><li>A circuit or portion of a circuit </li></ul></ul><ul><ul><li>that provides a single conducting </li></ul></ul><ul><ul><li>path without junctions </li></ul></ul><ul><li>Parallel Circuit </li></ul><ul><ul><li>A circuit or portion of a circuit in which two or more components are connected across a common point or junction, providing multiple conducting paths for the current </li></ul></ul>
  14. 14. Resistors in Series <ul><li>Resistors in series all have the same current </li></ul><ul><li>The total (or equivalent) resistance can by found by finding the sum of all resistors </li></ul><ul><li>R EQ = R 1 + R 2 + …. </li></ul>
  15. 15. Practice <ul><li>A 9.0 V battery is connected in series to four resistors with values of 2.0  , 4.0  , 5.0  , and 7.0  . Find the equivalents resistance for the circuit and the current in the circuit. </li></ul><ul><li>Hint: Draw a diagram! </li></ul><ul><li>Answer: R= 18  and I=0.50A </li></ul>
  16. 16. Resistors in Parallel <ul><li>Resistors in parallel have the same potential difference (voltage) across them. </li></ul><ul><li>The sum of the currents in parallel resistors equals the total current </li></ul><ul><li>Equivalent resistance is the sum of the reciprocals </li></ul><ul><li>1/R EQ = 1/R 1 + 1/R 2 + …. </li></ul>
  17. 17. Practice <ul><li>A 9.0 V battery is connected to four resistors in parallel with values of 2.0  , 4.0  , 5.0  , and 7.0  . Find the equivalents resistance for the circuit and the current in the circuit. </li></ul><ul><li>Hint: Draw a diagram! </li></ul><ul><li>Answer: R=0.917  and I =9.8 A </li></ul>