Electricity and Circuits

1. Electricity and Circuits Engineers in Training Day 2 Developed by Shodor and Michael Woody

2. Electricity • What uses electricity? • Name some things that use electricity • Try to name something you like to do that doesn’t use electricity. • Everything that uses electricity is made up of at least one circuit • To figure out how we use electricity we first will look at water.

3. Waterwheel • Suppose we want to grind some grain using a water wheel • What do you need to have a water wheel? • Water • Hill (for the water to flow down) • Pipes/channels (to direct the water) • The water wheel (to power something) • Mill, pump, etc (something needing power)

4. Waterwheel

5. Three Important Measures • What things might we measure about our water wheel setup? • How high/steep is the hill? • How fast is the water moving? • How much grain can we grind every day?

6. What about Circuits? • Our circuits are very similar to waterwheels. • Instead of a landscape we have a breadboard • This is where we put our circuit together

7. What about Circuits? • Our circuits are very similar to waterwheels. • We have electric charge instead of water • This is what makes everything go in the circuit

8. What about Circuits? • Our circuits are very similar to waterwheels. • And a battery instead of a hill • Without this the charges wouldn’t move, they would just stand still and do nothing.

9. What about Circuits? • Our circuits are very similar to waterwheels. • Wires for pipes and channels • These carry the electricity to where we want to go and direct it

10. What about Circuits? • Our circuits are very similar to waterwheels. • A light bulb (or motor, etc.) that needs power instead of the water wheel. • This is the end goal of our circuit, to accomplish some task.

11. Terminology • Voltage (potential) • This is like the height of our hill • The more voltage, the more the electricity wants to move • We measure this in Volts (V) • High voltage means more electricity (charge) will go through a wire

12. Terminology • Current (rate of flow) • This is like amount of water flowing • Current measures how much electricity is moving through a wire • This is measured in Amperes or Amps (A) • High current means a lot of electricity is moving (high current is very dangerous)

13. Terminology • Power • This is how much work our circuit does • Corresponds to how much grain is milled, etc. • Measured in Watts (W) • High Power = lots of work which can mean heat. • 100 W light bulb is hotter and brighter than 60W.

14. Lets Build a Circuit • We are going to build a circuit together now. • We will use the battery, the breadboard, the resistor, and the LED to make the LED turn on.

15. Breadboard • Breadboards are used to connect things quickly • You can proto-type circuits quickly

16. How to use your Breadboard • This diagram shows what holes are connected to each other. • You connect things together by plugging them in to holes connected to each other

17. Parts of Our Circuit • Battery • Source of constant potential (9 V)

18. Parts of Our Circuit • Wires • We have wires connected to our battery. + lead (red wire) – outflow from high potential - lead (black wire) – inflow to low potential

19. Parts of Our Circuit • Light Emitting Diode (LED) • Emits light when current flows through it • Current can only flow in one direction, from + to - (like a water wheel that won’t go in reverse) • Long lead (+) • Short lead (-) • Can be damaged by high current

20. Parts of Our Circuit • Resistor • Will keep our LED from getting damaged by too much current. • New term: • Resistance – how easy is it for current to flow • Symbol (R) • Unit (Ohm – Ω) • Circuit element • Resistor, like a wire • Regulates the flow of current • The higher the resistance the less current will flow • Current = Voltage/Resistance

21. Lets Build a Circuit • Use the battery, the breadboard, the resistor, and the LED to make the LED turn on. • Follow the “LED Circuit” in your handout. • Watch for polarity (plus minus signs) especially for the LED • Why is the resistor necessary?

22. Take a Break • When we come back we’ll look at some more electronic components and build a more complex circuit

23. Exercise • Go to http://falstad.com/circuit/ • Choose Circuits → Basic → Ohm’s Law • Ohms Law: V= I x R or I = V/R • In which branch will more current flow? • Imagine a networks of pipes

24. Capacitor • Like a glass that holds water • The more electricity flows in, the higher the voltage (water level) • It will eventually ‘fill up’ with electricity • A large capacitor is like a wide glass • Needs more water (electricity) to get to the same height (voltage) • For same voltage and resistance of the circuit, it will take longer to fill all the way up

25. 555 Timer Chip • Used to oscillate between a high (+5V) and low (0V) voltage • Stays high until the Threshold input rises above a certain level, then switches low and lets the attached capacitor start to discharge. • Stays low until Trigger falls below another level, then switches high and stops the capacitor from discharging.

26. Exercise • Go to http://falstad.com/circuit/ • Choose Circuits → 555 Timer Chip → Square Wave Generator • Build the circuit shown • Use the output to power the LED Circuit from first exercise • “555 Timer Circuit” in your handout gives the circuit, for convenience

27. The Circuit • The 555 timer will switch the output back and forth as the capacitor charges and discharges. • Before trying both capacitors, which one will make the light blink faster?