circuit stuff

7/31/2019 Circuit Stuff

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MOREWITHCIRCUITSName:_StanleyChu_________________

Period:__1__

Open the simulation here:http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc

Please note that you are expected to either sketch your circuit on this paperor paste in a picture of your circuit from the PhET simulation. Like the one atright!... You may also type directly into this document or print it out beforeyou start.

Experiment 1: One battery, one bulb, two wires, and then another wire!

Set up a single bulb circuit using 2 wires to connect the bulb to the battery.

1.1 A third wire will be added to the circuit, so that all of the current going through the bulb also has

to go through the added wire (aka in series).

A. If the bulb gets dimmer, what could we say about the current going through the circuit? Howwould this relate to the idea of resistance of the entire circuit?- If the bulb gets dimmer, that means there is a less of a current going through the circuit. Thismeans that the current is encountering more resistance.

B. If the bulb stays the same brightness, what could we say about the current going through thecircuit? How would this relate to the idea of resistance of the entire circuit?- If the bulb stays the same, then the current that is going through the circuit would be the same.

Therefore, that would mean that the current is not encountering any more resistance than it didbefore.

C. If the bulb gets brighter, what could we say about the current going through the circuit? Howwould this relate to the idea of resistance of the entire circuit?- If the bulb gets brighter, then that means the current going through the circuit would be moreintense. This would mean that there is less resistance going against the current. However, thiswould be impossible, as you cannot reduce resistance by adding wires.

D. Add the wire to the circuit and document the results.

The bulb lights up.

1.2 Instead of adding a wire, add different objects (at least 4) from the Grab Bag and documenteach effect on the bulb in the circuit.

Paper clip= The bulb lights up and is moderately bright.
http://phet.colorado.edu/en/simulation/circuit-construction-kit-dchttp://phet.colorado.edu/en/simulation/circuit-construction-kit-dc


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Dollar Bill = The bulb does not light up.Eraser = The bulb does not light up.Hand = The bulb does not light up.

1.3 Take one of the objects labeled resistor and add it to the circuit. Document the results.

The bulb becomes dimmer after the resistor is added.

1.4 Define in your own words the terms conductorand insulator.

A conductor is an object that has very low resistance, where currents can easily pass through theobject.

An insulator is an object that has very high resistance, where currents have a hard time passingthrough the object.

1.5 Metals are often categorized as conductors. Are all metals equal in their ability to conduct?

No, some metals like silver are more conductive than aluminum.

Experiment 2: Using an Ammeter

A light bulb can indicate the amount of current through a circuit or through a branch of a circuit. Anammeter also indicates flow, but instead of getting brighter, an ammeter gives a numerical value tothe current. Just like an indicator bulb, an ammeter must be part of the circuit (or part of a branchin the circuit) in order to measure the current. [Note: We are using the real ammeter, not theNon-Contact Ammeter!]

2.1 Set up a single bulb circuit. Now add a second bulb in series to the first bulb. How does theadding the second bulb affect the brightness of the first bulb.

- The first bulb becomes dimmer.

2.2 Set up a single bulb circuit. Now add the ammeter in series to the first bulb. How does theadding the ammeter affect the brightness of the first bulb. Sketch your circuit OR paste in ashot for your screen!


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2.3 What is the difference between using a bulb vs. an ammeter as indicators of current? Howwould you categorize an ammeter in terms of conduction and resistance?

- I think that ammeters are conductive because the brightness of the bulb was not reallyaffected. A bulb is an indicator of current because of the brightness, and the ammeter is anindicator of current because its shows how many amps are traveling throughout the circuit.

Ammeters measure current in Amperes (so confusing). Amperes are often called amps. TheletterI is used to represent current in physics equations, while the letter A represents the units ofcurrent, Amperes.

Experiment 3: Simple Series Circuits

In each of the following circuits, use the ammeter to measure the current through the entire circuit(in other words, the current going through the battery).

3.1 Multiple Resistors

A. Set up a circuit with a one resistor. Note that you can right click on the resistor to show thevalue for resistance, it should say 10.00 ohms. Document the current through the circuit and theresistance of the resistor

Resistor = 10 ohmsCurrent = 0.45 amps

B. Add another, identical resistor so that you have two resistors in series. Document the currentthrough the circuit and the resistance of each resistor. Sketch your circuit OR paste in a shotfor your screen!

Resistor = 10 ohmsCurrent = 0.3 Amps

C. If we had just one resistor, what would its value of resistance be so that it acted just like two10.00 ohm resistors? In other words, what is resistance of a single resistor that gives the samecurrent as two 10.00 ohm resistors in series? Check your answer. Sketch your circuit OR pastein a shot for your screen!

20 ohms

D. What big thing did this all show (or pretty much show)?


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- You can add the charges of resistors.

3.2 Repeat experiment 3.1 starting with one piece of 20.00 ohm resistor (right click to changevalue), two 20.00 ohm resistors, and then resistor that you predict will act the same as two 20.00ohm resistors. Document all of the results below

- A 40 Ohm resistor had the same effect as two 20.00 ohm resistors.

3.3 Starting with a circuit with only one resistor, develop a mathematic generalization for whathappens to the current when second, identical resistor.- The current would be cut in half E = I x R If R is doubled, I is halved.

3.4 Starting with a circuit with only one resistor develop a mathematic generalization for whathappens to the resistance of the circuit when you add a second, identical resistor.

The resistance would be doubled if there are two resistors. 2R

3.5 Predict what the current through the circuit would be for the following circuits; then check yourpredictions.

A. a 30.00 ohm and a 20.00 ohm resistors in series. I = -9/50

B. three 20 ohm resistors in series. I = -9/60

C. five 10.00 ohm and a one 50.00 ohm resistors in series. I = -9/100

Experiment 4: Simple Parallel Circuits

In each of the following circuits, use the ammeter to measure the current through the entire circuit(in other words, the current going through the battery).

4.1 Multiple Resistors in Parallel

A. Set up a circuit with one 40.00 ohm resistor. Document the current through the circuit.- 0.18 Amps

B. Add another 40.00 ohm resistor so that each resistor has its own connection to thebattery(these resistors are now inparallel). Document the current through the circuit.Sketch your circuit OR paste in a shot for your screen!


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C. Determine what single resistor would act just like two 40.00 ohm resistors in parallel?Document your results. Sketch your circuit OR paste in a shot for your screen!- 30 ohms

C. Now set up three 40.00 ohm resistors in parallel. Document the current through the circuit.

- 0.18 Amps

E. Determine what single resistor would act just like three 40.00 ohm resistors in parallel.Document your results. Sketch your circuit OR paste in a shot for your screen!- 40 ohms

F. When a branch is added in parallel, what general rule can you make about the current throughthe circuit and the resistance of the circuit?

[1/(1/R1 + 1/R2)] X I = E

4.2 Repeat experiment 4.1 starting with one, two, and then three 30.00 ohm resistors. Documentall of the results below. Sketch your circuits OR paste in a shots for your screen!

4.3 Develop a mathematic generalization for what happens to the current when you add branchesmade up of identical resistors.E/ [1/(1/R1 + 1/R2)] = I

4.4 Develop a mathematic generalization for what happens to the resistance when you addbranches made up of identical resistors.- [1/(1/R1 + 1/R2)] X I = E


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4.5 Predict what the current through the circuit would be for the following circuits; then check yourpredictions.- E/ [1/91/R1 + 1/R2)] = I

A. a 15.00 ohm and a 15.000 ohm resistors in parallel. I = -1.2

B. four 40.00 ohm resistors in parallel. I = -0.9

C. eight 40.00 ohm resistors in parallel. I = -1.8

D. a 40.00 ohm resistor and a 20.00 ohm resistor in parallel (super challenger!) I = -0.675

So far, you may have thought about resistance in terms of a bulb or a length of nichrome wire.Resistance has a formal definition; it is the ratio of the voltage across a component to the current

through the component or R . Resistance is measured in Ohms, which is symbolized with .

Does adding a resistor necessarily mean that the resistance of the circuit has increased? Explainyour answer.

No, the resistance only increases if the circuit is a series, not a parallel circuit.

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