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11/4/13switches and circuits

11/4/13switches and circuits. Science podcast : Getting Closer Electrical resistance Resistance relationships Review circuit building activity and results Review series vs parallel circuits Bulb brightness PhET circuit activity Switches House wiring

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11/4/13switches and circuits

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  1. 11/4/13switches and circuits • Science podcast: Getting Closer • Electrical resistance • Resistance relationships • Review circuit building activity and results • Review series vs parallel circuits • Bulb brightness • PhET circuit activity • Switches • House wiring • Homework: Electrical Power, Combination circuitsworksheet, read associated material.

  2. Learning objectives • Given a change in wire resistivity, length or cross sectional area, determine the change in resistance. • Compare/contract series and parallel circuits. How does current and electric potential vary in each? • Describe how the brightness of bulbs changes in series and parallel circuits when a bulb is added or taken away.

  3. Resistance and Ohm’s Law The resistance of a long, thin conductor of length L, cross sectional area A, and resistivity ρ is: The unit of resistance is the ohm. 1 ohm=1 Ω = 1 V/A. The current through a conductor is determined by the potential difference ΔV along its length:

  4. Resistance demo How will the resistance change if I … • Double the length? • Cut the length in half? • Triple the area? • Decrease the resistivity by a factor of five? Go over Resistance worksheet

  5. Circuit activity • Material: battery holders, one battery, 2 identical bulbs, 2 bulb holders, about 4 wires. • Construct 3 different circuits. In each case, note how the bulb brightness changes as you add a bulb • 1 bulb • 2 bulbs in series • 2 bulbs in parallel • Compare the brightness of the bulbs in each case • Describe what happens when you take out a bulb in each of the three circuits

  6. Circuit observations

  7. Two types of circuits – an analogy Added tollbooths increase flow Added tollbooths further restrict flow

  8. Series Circuits

  9. Parallel Circuits Go over Series and parallel worksheets

  10. Rate the bulbs from brightest to dimmest A D B E C F

  11. Practical difference between series and parallel circuits

  12. PhET Circuits activity (http://goo.gl/uYiX) Discuss activity and worksheets

  13. Simple switches Do the switch activity at your table

  14. Planning your house • With your house wiring group, design a plan for a room with a single switch controlling a light. • Design a plan for a single switch that controls two things with one being on at a time or both off. • Design a plan for an object that’s controlled by two switches such as a living room light that can be turned on and off from the front door or the kitchen. This is called a 3-way or double switch on the assignment sheet. • You should be able to power the object by moving only one switch or the other no matter the position of the 2nd switch. These switches must be apart from each other. • Test these out with your materials and using the PhET circuits simulation found at http://goo.gl/uYiX . • Share with the class.

  15. 1 switch that controls two things

  16. 1 switch that controls two things

  17. Simplest double switch (3-way switch)

  18. Simplest double switch (3-way switch)

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