1 / 49

DC Circuits

DC Circuits. Topics. Circuit Symbols 5 principles of DC Circuits 2 tips for solving DC Circuits Putting it all together – Electricity Problem Solving Toolkit. Circuit Symbols. Circuit Symbols ( pg 324). Sources of E.M.F.: Cell & Battery D.C. Power Supply A.C. Power Supply Resistor

almira
Download Presentation

DC Circuits

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. DC Circuits

  2. Topics • Circuit Symbols • 5 principles of DC Circuits • 2 tips for solving DC Circuits • Putting it all together – Electricity Problem Solving Toolkit

  3. Circuit Symbols

  4. Circuit Symbols (pg 324) • Sources of E.M.F.: • Cell & Battery • D.C. Power Supply • A.C. Power Supply • Resistor • Fixed Resistor • Variable Resistor (Rheostat) • Light Dependent Resistor (LDR) • Thermistor • Light Emitting Diode (LED) • Meters • Ammeter • Voltmeter • Switch • Light Bulb (Lamp) • Fuse • Bells • Variable Potential Divider (Potentiometer)

  5. Cell (Battery)

  6. D.C. Supply

  7. A/C Supply

  8. Fixed Resistor

  9. Variable Resistor (Rheostat)

  10. Light Dependent Resistor (LDR) • LDRs decrease their resistance when exposed to light • Often used as components for light-sensitive circuits (e.g. turn on lamps when it is dark)

  11. Thermistor • Thermistor’s decrease resistance when exposed to heat

  12. Semiconductor Diode • Allows current to flow in one direction • Blocks current in opposite direction

  13. Light Emitting Diode (LED) • Same as a diode, except now it emits light when current is flowing in the allowed direction

  14. Potentiometer • Also called “variable potential divider” • Is actually just a wire attached to a metre rule • Comes with an apparatus called a “jockey” • Will use this in the lab to prepare for SPA 2

  15. Ammeter

  16. Voltmeter

  17. Galvanometer

  18. Switch

  19. Light Bulb

  20. Fuse

  21. Bell

  22. Earth

  23. Transformer

  24. 5 principles of dc circuits

  25. Current in Series • In a series circuit (i.e. no parallel circuits), the current is the same at all points of the circuit

  26. Worked Example 1 • What is the reading of Ammeter X? Ammeter Reading = 0.2 A A A Ammeter X

  27. Current in Parallel • In a parallel circuit, there must be branches • Current follows the “what goes in must come out” rule

  28. Worked Example 2 • What is the value of I? 0.3 A I 0.2 A

  29. Worked Example 3 • What is the value and direction of current in wire X? 0.2 A 0.2 A X 0.3 A

  30. Potential Difference in Series • Total p.d. is equals to the sum of the individual p.d. components across the series • This is similar to calculating resistance of resistors in series • Note that p.d. across wire (without resistors) is zero

  31. Worked Example 4 • What are the readings of voltmeters X and Y? V V V 1.0 V 3.0 V Voltmeter X V Voltmeter Y

  32. Worked Example 5 • What is the reading of voltmeter X? V V 1.0 V Voltmeter X V 4.5 V

  33. Potential Difference in Parallel • p.d. is the same across parallel branches

  34. Worked Example 6 • What is the reading of voltmeter X? V 4.0 V V Voltmeter X

  35. Worked Example 7 • What is the reading of voltmeter X? V 4.0 V V V 1.0 V Voltmeter X

  36. Potential Divider Principle • The ratio of the resistances is the ratio of the p.d. • Equation form (not recommended to memorize): • V1 = [R1/(R1 + R2)]Vɛ

  37. Worked Example 8 • What is the reading of the voltmeter? 3 V 1 Ω 1 Ω V

  38. Worked Example 9 • What is the reading of the voltmeter? 3 V 1 Ω 2 Ω V

  39. Worked Example 10 • What is the reading of the voltmeter? 5 V 3 Ω 4 Ω V

  40. How is a potential divider useful? • Let’s say I only have a 10 V battery, but I only need 5 V of emf for a circuit. I can use a potential divider to “divide up” my 10 V battery into just 5 V. 10 V R R

  41. Potentiometer • However, using resistors to divide up emf is inflexible. We cannot change the ratio easily (need to change the resistors manually). • An easier method is to use a potentiometer (or variable potential divider)

  42. Potentiometer 50 cm 50 cm R V R/2 R/2 V

  43. Worked Example 11 • What is the reading of the voltmeter? 5 V 30 cm 70 cm V

  44. Worked Example 12 • State and explain what will happen to the lamp as the jockey slides from the 0 cm mark to the 100 cm mark. 5 V 0 cm 100 cm

  45. Worked Example 13 • Potential divider circuits may also involve the use of LDRs and Thermistors • Design a circuit which switches on a lamp automatically when it turns dark (hint: when bright, p.d. across lamp is low. when dark, p.d. across lamp is high)

  46. 2 tips for dc circuits

  47. Redraw Circuit Diagrams

  48. Replace Resistors in a Cluster

  49. Electricity Problem Solving Toolkit 4 equations • Definition of Current • Definition of Resistance • Electrical Power • Electrical Energy 2 arrangements of Resistors • In series • In parallel 5 Principles • Current in Series • Current in Parallel • P.d. in series • P.d. in parallel • Potential Divider 2 tips • redraw diagram • replace parallel resistors

More Related