Electric Circuits: Building and Understanding Circuits with Physics Principles

Computer

1. Define and utilize the physics principles of electrical circuits.

Circuit Building:

To begin with, please proceed to the following website:

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc-virtual-lab/latest/circuit-construction-kit-dc-virtual-lab_en.html

Once you are there, you should see a screen that looks like this

1. Let’s start out “easy” by making a light bulb light up.  Use ONLY one battery, two wires, and a light bulb.  You may want to refer to the textbook for help in what each component in a circuit should look like.  Take a screen-shot of your lite bulb and place it below.

2. What seems to be making the light bulb turn on in your circuit?  (what do you think electricity is based on the simulator?)

3. Make a gap in the circuit, then go to the grab bag and test each of the items there to see if they allow #2 to happen.  Do so by placing these items in the gap you just created.

4. Now take two bulbs, and one battery, and as many wires as you like, and create a circuit which makes BOTH bulbs light up, but when the connection is broken, BOTH bulbs go out.  Once you have found the correct mechanism, attach a screenshot of your circuit below:

5. Why did BOTH bulbs go out when you broke the connection?

This is called a series circuit where all circuit components are in one line.  The line is not necessarily straight!  

6. Now take your two bulbs, a battery, and as many wires as you like, and make a circuit which lights BOTH bulbs, but when you break the connection, only ONE bulb is not light. Attach a screenshot of the circuit below.

 
7. When you break the connection, why does one bulb stay light?

This is called a parallel circuit and contains two, or more!, individual loops that connect to the battery.

8. Now add in a third bulb, keeping the one battery, and as many wires as you like, create a circuit which has BOTH series and parallel components, which also lights up all three light bulbs. Once you have this completed, attach a screenshot below.

9. You design toys for a toy company.  Your boss wants you to hook up the lights in the toy car you are working on in the cheapest way possible, without consideration of the quality of the toy.  Which circuit should you use if you want to save money by using fewer parts?  Why would this circuit be cheaper?

10. You are an electrician working on a house. What type of circuit should you use for the house so that the owners don’t call to complain about their wiring?  Why use this circuit?

It’s sufficient to say that a light bulb behaves pretty similar to a resistor.  Something that “resists” the flow of electricity.  Why would we want something to resist the flow?  For the very reason we like to have a light bulb in a lamp to read at night.  The energy taken from the flow can be converted into many other forms, including light!  Sometimes resistors are useful in “reducing” the electric potential energy so it does not overwhelm a single electrical component.  For example, power lines can have up to 750,000 Volts running through them!  Your outlet at home has 110V.  Imagine plugging in your cell phone directly into the powerlines!  It would likely explode!  

So let’s take a moment to quantify resistors!  It’s worth noting at this point that

• To measure current with an ammeter, you must put the ammeter in SERIES with the component you want to measure current for.
• To measure voltage with a voltmeter, you must put the voltmeters in parallel with the component you want to measure voltage for.
• Here is a screenshot of how one might plug in each sensor to measure the voltage and current in one resistor.

• Figure #2

11. Now try setting up a circuit with two resistors in series, and measure the current and voltage for each resistor.  Take a screenshot of the circuit you build in the simulator and attach it below.

12. In the area below, write in the currents and voltages for each resistor, and write a summary statement which explains voltage and current in a series circuit, i.e. “The current is constant everywhere in a series circuit.” or similar.

13. Now try setting up a circuit with two resistors in parallel and measure the current and voltage for each resistor. Take a screenshot of the circuit you build in the simulator and attach it below.  
 

14. In the area below, write in the measurements for each resistor and write a summary statement for voltage and current in a parallel circuit.

15. Now try putting three resistors in a circuit that contains BOTH a series portion and a parallel portion.  Attach a screenshot of your circuit below.

16. Write out the values for current and resistor for each resistor.  Then confirm that they comply with your statement in questions #16 and #18.

Questions #11-#16 summarize what are known as Kirchhoff's Loop and Junction rules of electricity.  With these laws, one can simplify the math of even the most complex circuits.