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04-03-08 - Circuit Calculations


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04-03-08 - Circuit Calculations

  1. 1. Circuit Calculations
  2. 2. the flow of charged particles ; can be positive or negative, but usually negative (electrons) through a conducting metal
  3. 3. Field lines point away from positive and toward negative charges . An electric field exists in a region in space if a charge placed in that region experiences an electric force. Electric Fields
  4. 4. Write this down! Ω (ohm) A (ampere) V (volt) Units R=V/I V is voltage I is current R Resistance I=Q/t Q is charge T is time I Current V = W/Q W is work Q is charge V Electric Potential Difference (a.k.a. voltage) Formula Symbol Quantity
  5. 5. Electric Potential Difference (a.k.a. voltage) the change in electric potential energy per unit charge V = W / Q The SI unit of electric potential difference is the volt , named in honor of Alessandro Volta . One volt is the electric potential difference between two points when one joule of work is done in moving one coulomb of charge between the points.
  6. 6. Voltmeter a device that measures electric potential difference
  7. 7. Electric current (I) is measured in amperes , in honor of Andre Marie Ampere . One ampere is the flow of one coulomb of charge per second. 1 amp = 1 coulomb per second = 1 C/s I = Q / t
  8. 8. Ammeter a device that measures current attached in series
  9. 9. Resistance determines the amount of current flow = the ratio of potential difference to current R = V I The SI unit of resistance is the ohm ,  , named in honor of Georg Simon Ohm . One ohm of resistance is the resistance such that one volt of potential difference is needed to obtain a current of one amp .
  10. 10. power = work / time = ( work / charge ) . ( charge / time ) = electric potential difference . current P ( Watts ) = V ( Volts ) . I ( Amps )
  11. 11. Ohm’s Law The ratio of potential difference to current is constant. If R = V/I is a constant value for a given resistor, then that resistor is said to obey Ohm’s Law.
  12. 12. Kirchhoff’s Rules Loop Rule: The sum of the potential differences (voltage) around any closed circuit loop is zero.
  13. 13. Kirchhoff’s Rules Junction Rule: The sum of the currents into any circuit junction is zero.
  14. 14. The site linked here allows you to build and test your own series, parallel, and/or combination circuits.