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Circuits

Circuits. What will happen to bulbs 1 and 2 when you disconnect the wires at various points?. LAB 21. Consensus: Current requires a closed loop. What type of object, when inserted into the loop, will allow the two test bulbs to light?. LAB 22. Consensus:

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Circuits

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  1. Circuits

  2. What will happen to bulbs 1 and 2 when you disconnect the wires at various points? LAB 21 Consensus: Current requires a closed loop

  3. What type of object, when inserted into the loop, will allow the two test bulbs to light? LAB 22 Consensus: Current requires a closed loop made entirely of conductors.

  4. What parts of a socket and bulb are conductors and which are insulators? What is the conducting path through the bulb? Clips Base Fig 2. Clip – side view Plates LAB 23 Consensus: Trace the Continuous Conducting Path (CCP) through the bulb.

  5. Schematics Schematics are drawings used to show circuits using symbols instead of actual drawings. Here are some examples:

  6. Schematics Even though you have a list of several useful symbols in your book. Here are a few more:

  7. Schematics Draw a schematic of a circuit consisting of a battery made of 2 cells (label + and – ends) and two light bulbs.

  8. Schematics Draw a schematic of a circuit consisting of a battery made of 3 cells (label + and – ends), a light bulb and a resistor.

  9. Schematics Draw a schematic of a circuit consisting of a battery (label + and – ends), three light bulbs, an ammeter and a voltmeter on the second bulb.

  10. Schematics A visual representation of a circuit is shown below. On the right, sketch the corresponding schematic diagram.

  11. Worksheet 2 1.

  12. Worksheet 2 2.

  13. Worksheet 2 • 3. bulb 1: Lit Unlit bulb 2: Lit Unlit

  14. Worksheet 2 • 4. bulb 1: Lit Unlit bulb 2: Lit Unlit

  15. Worksheet 2 • 5. bulb 1: Lit Unlit bulb 2: Lit Unlit

  16. Worksheet 2 • 6. bulb 1: Lit Unlit bulb 2: Lit Unlit

  17. Worksheet 2 • 7. bulb 1: Lit Unlit bulb 2: Lit Unlit

  18. A B C How does the number of bulbs in a single loop affect the overall resistance of the circuit? Consensus: As resistance in a single closed loop goes up, the current goes down. R R R SERIES CIRCUIT LAB A A A

  19. SERIES CIRCUIT LAB Consensus: For a series circuit, the voltage across the whole circuit is equal to the sum of the individual voltage drops. For a series circuit, the total current flows through each resistance on the loop.

  20. Series Circuits Series circuits – circuits where all sources of resistance are on a single closed loop with the battery.

  21. Series Circuits Total Resistance = the sum of all resistances. R = R1 + R2 + R3… This means that two 8-W resistors could be replaced with one 16-W resistor.

  22. Series Circuits Voltage drop = the voltage pulled from the battery by a resistance to produce current. Total voltage = the sum of the voltage drops across each resistance.

  23. “Rules” for Series Circuits • Total resistance = sum of all resistances R = R1 + R2 + R3 + … 2. Total voltage = sum of voltage drops = battery V = V1 + V2 + V3 + … • Voltage drop – use Ohm’s Law V1 = I (R1) 4. Total current is the same throughout I = V/R

  24. Suppose you have three 3-W resistors connected in series to a 9-V battery. What is the total resistance? 9 W What is the current in the circuit? 1 A What is the voltage drop across each resistor? 3 V Series Circuits

  25. Series Circuits There are three 20-W resistors connected in series across a 120-V generator. What is the equivalent resistance of the circuit? What is the current of the circuit? What is the voltage drop across each resistor? R = R1 + R2 + R3… R = 20 + 20 + 20 R = 60W I = V/R I = 120V/60W I = 2 A V = IR V = 2A(20W) V = 40 V

  26. Series Circuits A 10-W resistor, a 15-W resistor and a 5-W resistor are connected in series across a 90-V battery. What is the equivalent resistance of the circuit? What is the current in the circuit? What is the voltage drop across each resistor? I = V/R I = 90V/30W I = 3 A R = R1 + R2 + R3… R = 10 + 15 + 5 R = 30W V = IR V = 3A(10W) V = 30 V V = IR V = 3A(15W) V = 45 V V = IR V = 3A(5W) V = 15 V V = 30V + 45V + 15V = 90V

  27. PARALLEL CIRCUIT LAB How does the number of bulbs along side affect the overall resistance? Consensus: Bulbs alongside create their own closed loop increasing the amount of current overall. This is the opposite of bulbs in series. New Terms: Parallel circuit A A A

  28. PARALLEL CIRCUIT LAB Consensus: The voltage drop across each lamp is equal to the total across the battery.

  29. A a A A A A c b d e L L L L f A PARALLEL CIRCUIT LAB Consensus: The total current in the circuit is equal to the sum of the currents in each lamp.

  30. Parallel Circuits Parallel circuits – circuits where each source of resistance is on its own closed loop with the battery.

  31. Parallel Circuits Total Resistance = sum of the inverses of each resistance 1/R = 1/R1 + 1/R2 + 1/R3… This means that two 8-W resistors in parallel could be replaced by one 4-W resistor.

  32. Parallel Circuits Voltage drop In a parallel circuit, the voltage drop is the same across each branch, equal to the battery.

  33. Parallel Circuits Current In a parallel circuit, the total current in the circuit is equal to the sum of the currents in each branch.

  34. “Rules” for Parallel Circuits • Total Resistance = inverse-sum of inverses 1/R = 1/R1 + 1/R2 + 1/R3 + … • Voltage drops on each branch = battery • Total current (found using Ohm’s Law) = sum of currents in each branch I = V/R I = I1 + I2 + I3 + … • Current in each branch uses Ohm’s Law I1 = V/R1

  35. Suppose you have three 3-W resistors in parallel connected to a 9-V battery. What is the total resistance of the circuit? 1 W What is the current in the circuit? 9 A What is the voltage drop across each resistor? 9 V What is the current in each resistor? 3 A Parallel Circuits

  36. Parallel Circuits Three 15-W resistors are connected in parallel and placed across a 30-V potential difference. What is the equivalent resistance of the parallel circuit? What is the current through the entire circuit? What is the current through each branch of the parallel circuit? I = V/R I = 30V/5W I = 6 A 1/R = 1/R1 + 1/R2 + 1/R3… 1/R = 1/15 + 1/15 + 1/15 1/R = 3/15 R = 15/3 = 5W I = V/R I = 30V/15W I = 2 A

  37. Series and Parallel CircuitsAn Analogy

  38. LAB 28 What is the effect of adding a bulb in parallel? Consensus: Adding a bulb in parallel to a series circuit causes a split of the current to the two parallel branches and an increase in the total current. New Terms: Combination Circuit – a circuit with both series and parallel parts.

  39. Combination Circuits Combination circuits – those circuits that contain both parallel and series portions.

  40. Combination Circuits There are steps to take to find the total resistance: 1) Find the total resistance for any parallel parts. 2) Add that to any resistance in series.

  41. Combination Circuits Sometimes there are more steps to be taken: • Start with the smallest section of parallel. • Add any in series. • Then add as if two resistances in parallel. • If there are still some in series, then add those.

  42. Combination Circuits You can also do the same thing if each branch of the parallel portion has some in series:

  43. Worksheet 35-2

  44. Worksheet 35-2

  45. Worksheet 35-2

  46. Worksheet 35-2

  47. Worksheet 35-2

  48. Worksheet 35-2

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