Download
lesson 6 n.
Skip this Video
Loading SlideShow in 5 Seconds..
Lesson 6 PowerPoint Presentation

Lesson 6

99 Vues Download Presentation
Télécharger la présentation

Lesson 6

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Lesson 6 Lesson 6 Direct Current Circuits • Electro Motive Force • Internal Resistance • Resistors in Series and Parallel • Kirchoffs Rules

  2. Topics • RC Circuits • Charging • Discharging Capacitors • Electrical Instruments • Galvanometer • Ammeter • Voltmeter • Wheatstone Bridge • Potentiometer

  3. EMF I Electro Motive Force (emf) Source of emf is any device that increases the potential energy of charges circulating in a circuit. Electric Potential increases by the emf Eas charge goes from negative to positive plate of battery.

  4. EMF II EMF is Work Done per unit charge by electrical pump e dW = dQ

  5. Charge Pump • Battery is a Charge Pump • Current flowing internally in battery feels a resistance this is an • Internal resistance, r • Flowing positive charges (current)experience drop of electric potential in resistor V=IR + - R

  6. Internal Resistance - - - + + + Terminals • Terminal Potential Difference • V = E - Ir

  7. Picture

  8. Power and Internal Resistance

  9. Combination of Resistors Combinations of Resistors • Parallel • same electric potential felt by each element • Series • electric potential felt by the combination is the sum of the potentials across each element

  10. Series

  11. Parallel

  12. Kirchoffs Rules I Kirchoff’s Rules The sum of the currents entering a junction must equal the sum of the currents leaving Conservation of Charge

  13. Kirchoffs Rules II The Sum of the Potential Differences around a closed circuit loop must be zero Conservation of Energy

  14. Picture

  15. RC circuits RC Circuits • Non Steady State • Non Equilibrium • Current varies with time

  16. Picture

  17. Charging I

  18. Charging II q e - - = IR 0 C æ ö e d q dI 1 dq - - = = - - ç ÷ IR 0 0 R è ø dt C dt C dt dI I Û + = R 0 dt C dI 1 Þ = - dt I RC ò ò t I dI 1 Þ = - dt I RC I 0 0 æ ö t I t - ( ) Þ ç ÷ = - Û = ln I t I e RC 0 è ø I RC 0 e t - ( ) = RC I t e R

  19. e Charging III t - ( ) = RC I t e R e t dq - = e RC dt R e t - Þ = RC dq e dt R ò ò q t e t - = dq e RC dt R 0 0 é ù é ù t t e - - e e ê ú ê ú ( ) RC RC Þ = - = - C q t 1 Q 1 ê ú ê ú ë û ë û

  20. Time Constant

  21. Discharging I Discharging +Q -Q q = IR from Kirchoff C dq = - I the rate of decrease of charge dt

  22. Discharging II