You are required to lead a lab activity with the class



Template for Computational Science Related Lessons

Title of Lesson: Electrical Engineering and Circuits

Grade level / course: Middle School

|Objectives / Concepts |

|Lesson Abstract: |

|Learning about more complex circuits, including using capacitors and Integrated Chips to build a circuit |

| |

|Standards Addressed: |

| |

|Objectives: |

|Students will understand the concept of a capacitor and how its size affects how it performs |

|Students will be introduced to a Integrated Circuit (IC) chip, the 555 Timer |

|Students will be able to build a circuit using the 555 Timer which makes a LED blink |

|Students will understand how to change the speed at which the LED blinks using the capacitor |

|Prerequisite knowledge: |

|Students should have learned about basic circuit elements including |

|Batteries |

|Wires |

|Resistors |

|LEDs |

|Breadboards |

|Ideally the Students learned about all these things through an analogy with a water wheel |

|Students should have built a simple circuit with battery, resistor, and LED on breadboard |

|Teacher preparation: |

|Assemble bags and breadboards with all necessary components |

|Explore the applet site to help students find the right example circuits |

|Required Materials |Media (software, websites, overhead, |Equipment (computer, display, OHP, VCR, |

|(What and how much) |transparencies, video, etc) |etc) |

|Circuit Components (for each student) |Falstad circuit simulator |computers |

|1 x Breadboard | |projector |

|1 x LED | | |

|1 x 555 Timer | | |

|1 x 10 (F Capacitor | | |

|1x 100 (F Capacitor | | |

|3x 10 k( Resistors | | |

|1x short (5 cm) red wire | | |

|1x short black wire | | |

|1x short blue wire | | |

|1x 9V battery | | |

|1x 9V battery leads | | |

|Circuit Diagram Layouts | | |

|Safety (Precautions and reminders) |

|Do not work on the circuit with the battery connected for safety of the circuit and the builder |

|Be careful of polarity with capacitors and LEDs and with the connections to the 555 timer. All of these components are damaged by |

|incorrect polarity or high currents and can smoke, or get very hot. |

| |

|Presentation Outline |

|Time | Event |

| | |

|Introduction/ Review |You just learned about several different components of a circuit and built a simple circuit yourself. |

| |Lets go over the different components we used. |

| | |

| |Ask the student which components they used and what each component corresponded to in the water wheel |

| |analogy (if the analogy was used). |

|5 min | |

| |Should Recall: |

| |Breadboard is like the landscape |

| |Battery is like the Hill |

| |Wires are like the pipes or channels |

| |Light bulb/LED is like the water wheel |

| |Introduce a new circuit element, the capacitor. |

| | |

|Capacitor |Explain that the capacitor is like a water tank of glass |

| |As water comes in the tank fills up |

| |The faster the water comes in the quicker it fills up |

| |Can only fill to a certain point |

| |A larger (wider) tank fills up more slowly than a narrow |

|10 min |Likewise for a capacitor: |

| |Current flows in and fills the capacitor, raising the voltage of the capacitor |

| |It fill up faster with higher currents |

| |Only will fill up to the supplied voltage |

| |Larger capacitors take longer to charge |

| |Show the circuit diagram representation of the capacitor |

| |Be sure to emphasize the polarity of the capacitor and how the long lead is the positive one. Have |

| |students look at the markings themselves. |

| |Next Introduce the 555 timer |

| |Explain how it is an Integrated Chip or just a chip, which is very complicated on the inside. |

| | |

|555 Timer |It is used for timing in many things because it turns things on and off at certain times: |

| |Examples : Car windshield wipers, interior lights, etc |

|10 min | |

| |The chip is controlled by the voltage on the capacitor. When the voltage is high, the output is off; |

| |when the voltage goes lower, the output turns on. |

| | |

| |Also the chip controls when the capacitor charges and discharges, so it keeps everything going in a |

| |loop. |

| | |

| |Show them a chip and explain how the pins correspond to different functions, but we don’t need to |

| |worry too much about them. |

| | |

| |The chip needs power just like our circuit needs its own power since there’s just more circuits inside|

| |the chip |

|Computer Applet |Have the students go to the applet which shows the circuit they will build: |

| |ž |

| |žChoose Circuits → 555 Timer Chip → Square Wave Generator |

| | |

|10 min |Get the applet up on your screen so you can show it to them. |

| | |

| |Ask the students to identify each component on the diagram. |

| |Point out how the power and ground act like the positive and negative terminals on our batteries |

| | |

| |Point out the graphs at the bottom showing the voltage on the capacitor (green graph on left) and the |

| |output voltage. You can see the capacitor charging and discharging as the output goes on and off. |

| | |

| |Slow down the animation so they can watch the current flow in to the capacitor and see the voltage |

| |rise. Then point out how when it gets to a certain point, the chip changes the output to low, then the|

| |capacitor discharges through the chip. Try to make sure they understand. Tell them we are going to |

| |build this circuit but with an LED on the output of the chip |

|Building the 555 Circuit |Everyone should already have the parts they need and a circuit diagram handout. Pull up the circuit |

| |diagram on the projector. |

| | |

| |Step the students through the wiring process one step at a time. Make sure almost everyone is caught |

| |up before continuing. First start by explaining how to use the rails or buses on the breadboards to |

|30 min |supply power. Plug the battery connection wires into the right red rail (the red wire) and the |

| |leftmost blue rail (the black wire). Remind students not to attach the battery yet. |

| | |

| |Next have the students carefully put in the 555 chip, making sure the little dot on the top is |

| |pointing up (having everyone do it this way not only assures consistency when we are explaining the |

| |circuit, it also puts the correct power buses on the right sides of the chip) |

| | |

| |Next have them wire the power and ground to the chip, using the red wire for + and black wire for -. |

| |Explain how we follow this convention to make things look simpler. Then make connections between the |

| |chips pins using the resistors and the blue wires. As you make each connection, cross off or check the|

| |corresponding wires on the diagram on the screen. |

| | |

| |Then put the capacitor (have everyone use the smaller one) into the circuit, making sure it’s put in |

| |the right way. Finally the resistor and LED should be put in, reminding the students how to use their|

| |breadboards and that the LED can only go one way. Also remind students of how this is almost exactly |

| |like the circuit they built earlier. |

| | |

| |Finally the students can connect the battery and test the circuit. Help any student’s whose aren’t |

| |working, making sure to check that the wires are pushed in enough, they are to the right places, the |

| |LED is not faulty or burned out. If the 555 timer feels hot to the touch, it probably needs to be |

| |replaced. |

|Exploring the 555 Circuit |When the students are done building their circuits, ask them how they could change how fast their |

| |light blinks. Make sure they understand that a bigger capacitor will take longer to charge and thus |

|10 mins |the light will remain off longer and on longer. |

| | |

| |Have them come up with a guess, then unplug the battery and change the capacitor. Where they right? |

| | |

| |Ask them if there is any other way to change how long the light is on. Hint at other ways to change |

| |the time, like giving it less current. If you have different sized resistors and want to have them try|

| |it you can. |

|Reflections |Reflections |

|15 min | |

|Extra Time |The students can explore other circuits on the applet site if there is extra time. Also, if there’s a |

| |lot of time, a brief introduction to digital electronics could be useful. |

|Bibliography |

|Part of this lesson, including the 555 circuit was originally designed by Professor Dr. Rhett Davis of NC State University |

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