Ms. Haber's Science - Home



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Intro to circuits

1. For a light bulb to glow you must have a complete loop, the two poles of a battery must be connected to the light bulb with conducting wires. Use your understanding of the role of a battery and of conductors to explain these observations using two analogies: one involving flowing water and the other involving a group of people running on a track. Remember the analogy does not need to account for all aspects of the circuit. However, if you find similar aspects, make a note of them.

|Parts of the electric circuit |Parts of the water system |Parts of the running people system |

|Moving electrons | | |

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|Battery | | |

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|Connecting wires | | |

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|Lightbulb | |Muddy patch on the track |

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|Observed properties of the electric current |Properties of the water system |Properties of the running people system |

|When bulbs are in series, the light bulbs are | | |

|less bright. | | |

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|When identical bulbs are in parallel the light | | |

|bulbs are the same brightness. | | |

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Definitions:

Voltage:

Current:

2. Analogy continued

a. Describe an analogy between some part of a system with water flow in a pipe caused by a pump and the potential difference (voltage) provided by a battery in a circuit.

b. Describe an analogy between some part of a system with water flow in a pipe caused by a pump and the physical quantity electric current in a circuit.

3. Circuit Diagrams

a) A circuit diagram is a representation that uses symbols to show the components in a circuit and how they are connected:

|Symbol |[pic] |[pic] |[pic] |

|Meaning |battery |light bulb |switch |

|Notes |The long side indicates the positive |Both sides must be connected|A switch is drawn as "open" in a |

| |end of the battery |for the bulb to light |circuit diagram. |

|Symbols can be drawn in any | |[pic] |[pic] |

|orientation | | | |

|Wires connect at the points shown | |[pic] |[pic] |

|with X | | | |

b) Fill in the table below with some other symbols:

|Part of Circuit |Sketch |Schematic Symbol |Notes (what does this element |

| | | |do?) |

|Resistor | | | |

| | | | |

|Ammeter | | |Measures current through |

| | | | |

|Voltmeter | | |Measures potential difference |

| | | |across |

|Ground | | | |

Ohm’s law observation:

4. You connect a resistor in series with an ammeter and a variable potential difference source. In the table, the electric current I through the resistor is shown as you vary potential different ∆V across the resistor.

|Potential difference | | | | | | |

|(V) | | | | | | |

|Current I (A) | | | | | | |

Complete the following

|Construct a circuit diagram: |Represent the data graphically: |

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|Describe the pattern mathematically: |Explain the relationship between the current through the resistor and the potential difference across|

| |it: |

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Practice

a. Diagram a circuit that is similar to this picture of an obstacle course with coach, runners, and mud puddles.

[pic]

b. In the electric circuit, what is the equivalent of the coach? How are the roles of the two elements similar? How are they different?

c. In the electric circuit, what is the equivalent of the runners? How are the roles of the two elements similar? How are they different?

d. In the electric circuit, what is the equivalent of the mud puddles? How are the roles of the two elements similar? How are they different? Explain the arrangement of the two elements?

e. Diagram a circuit that is similar to the picture of a water system with pumps, pipe, and a water wheel.

f. In the circuit, what is the equivalent of the pumps? How are the roles of the two elements similar? How are they different? What is the meaning of their arrangement?

g. In the circuit, what is the equivalent of the water wheel? How are the roles of the two elements similar? How are they different?

h. Complete the analogy “height: water = _____________: electrons.” Explain:

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