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PHYS 100 – Simple Circuits TITLE: Simple Circuits Objective: To become familiar with Simple Circuits

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PHYS 100 – Simple Circuits TITLE: Simple Circuits Objective: To become familiar with Simple Circuits. To construct a complete electrical circuit, and to represent electrical circuits with circuit diagrams. To determine how light bulbs behave in different circuit arrangements. The different ways of connecting two batteries will also be investigated. To begin experimenting with variables which contribute to the operation of series, parallel and combinations of circuits. Theory: In class, we have been focused on Static Electricity. In lab, we are going to see what happens when charges start to move. Consider a simple wire connected to a battery. In general, there are three things that are important to talking about the electricity in the wire. The Current (I) describes how many and how fast the charges are moving. It is measured in units of Amperes (A or Amp). It is the number of Coulombs that move through a wire in one second. The movement of the charges is caused by a Potential Difference between the two ends of the wire. The Potential Difference (?V) comes from the battery. Each end of the battery is at a different potential. When we connect the wire between the two ends, the difference is bridged and charges will flow. This is also called the Voltage because it is measured in Volts (V). The last concept has to do with the wire itself. Some wires allow charges to flow more easily than others. The property of the wire that determines how current will flow is called the Resistance (R) of the wire. Resistance is measured in Ohms (?). All of these concepts are related through Ohm’s Law (It’s his law, that’s why he gets to name the unit): ?? = ?? Mathematically, Ohm’s law says what I just said. A Potential Difference in a source (like a battery), causes Current to flow (like in a wire), but the amount of current is impeded by the Resistance of the conduit (the wire itself). Components in a circuit can be combined in series, in parallel or a combination of both. Components that are in a series are connected such that each component is in line one after another. Components in parallel are hooked up so that they are connected independent of one another. Holiday lights are often hooked up so that bulbs of one color are in a series with each other, all on the same wire. The Red lights in the figure are in series with each other. The Blue lights are also in series with each other. The two different colors of lights are in hooked up to the power source separately. The Blue lights are in parallel with the red ones. This isn’t always the case with lights, but a good way to tell is to pull one of the bulbs out. If all of the lights of that color go out, they are in Series. In this lab, we are also going to use standard symbols in our circuit representation. Some objects in this representation are shown below. wire switch resistor bulb battery voltmeter ammeter You may have noticed, but kindly did not remark, that the colored lights above are a mess to look at. The standard representation allows the bulbs to look a little neater. Here are the same bulbs (although not quite so many!) in circuit diagram representation. 1 PHYS 100 – Simple Circuits Here Is the On-Line Resource to Use for Running the Simulations or Our Remote Lab on Circuits: https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc Setup: Click on Intro. You should see a blank screen that is your Lab Table. On one left side, there are components that you can put into your space. To use a component, just click on the item and drag it into the space. Use the wires to connect components together. You can double click on any connection to show the scissors icon in order to cut the connection. The delete button works as well. The right side has the Measurement Tools (Voltmeters and Ammeters) that you can also select and drag into your space to use. There are also settings that are used for this lab. Right now, the “battery” is highlighted to indicate that the components are shown in “real life” pictures. If you click the symbol, it will switch your view to the circuit diagram representation. 2 PHYS 100 – Simple Circuits SIMPLE CIRCUITS Type Here Your Full Name_____________________________________________________ (**********This is an ACTIVITY lab. The procedure, data, and analysis are combined***********) PART A: Bulbs in Series and Parallel: Use the URL referred above and start connecting the elements of the simple electric circuits. Choose one battery, one bulb and two wires. Connect the components to make the light bulb light up. Draw your circuit here using the symbols from the Theory Section (right above on page 1.). Insert here one screen shot of the successfully produced, working circuit. Adjust the size of the photo that proves the completion of this first step. Add a second bulb such that it is in a Series with the first bulb using only one extra wire. Draw your circuit here using the symbols from the Theory Section (right above on page 1.). Insert here one screen shot of the successfully produced, working circuit. Adjust the size of the photo that proves the completion of this specific step of the lab. • Is your original light the same brightness, or was it brighter or dimmer than it was with just one light? Can you explain any differences in the brightness or why it is the same? • If one of the light bulbs is disconnected does the other bulb go out or does it stay on? Explain why or why not. • Add a third bulb in a series. What happens to the brightness of the bulbs? Leave your series circuit on the desktop. Recreate your simple circuit and add a second bulb using two extra wires bulbs are now in parallel with the battery. 3 PHYS 100 – Simple Circuits Sketch the connections that you made in the form of a circuit diagram using standard symbols (as before; now you know from where to take them.). Insert here one screen shot of the successfully produced, working circuit. Adjust the size of the photo that proves the completion of this specific step of the lab. • Continue by answering to the questions below. Are the bulbs in this circuit brighter or dimmer than when they were in a series? Why do you think this is? • If one of the light bulbs is unscrewed, does the other bulb go out or does it stay on? Explain why or why not? PART B: Batteries in series and parallel Use the same URL of the simulation to create different other connections and to answer to the questions below. Clear your desktop and connect a single battery to a single light as in the first circuit of part A. Note the brightness of the light. • Now connect a second battery into the circuit so that it is in series with the first (you will only need one wire at the most. The diagram should look like batteries in a Flashlight). What is the effect on the brightness of the light? • Connect the second battery so that it is in parallel with the first (You will need two wires). What is the effect on the brightness? • Which of these was the most useful in making the light brighter? Which was the least useful? Can you determine the reason why each behaved as it did? PART C: Measuring Devices Use the same URL of the simulation to learn how electric measuring devices (voltmeters, ammeters) work. 4 PHYS 100 – Simple Circuits Go back to a single bulb and battery. We are going to add some measuring devices. A voltmeter is a device that measures the Potential Difference or Voltage. Pull the voltmeter into the space. The voltmeter is usually connected in parallel to the component of the circuit that you are trying to measure the voltage of. Put the red end of the voltmeter on one end of the battery and the black end on the other. • What is the value on the Voltmeter? • Switch the leads on the voltmeter. What do you think that the sign on the measurement means? Use the Voltmeter to measure the Potential Difference or voltage across the bulb. This value tells us how much voltage the bulb is getting. • How does the value of the voltage across the bulb compare with the battery? Pull the Ammeter into the space. This is a “non-contact” ammeter. An ammeter is used to measure the current that flows in a circuit. Usually, the ammeter is connected in series with the other components. Connecting an ammeter usually requires us to “break” the circuit in order to put the ammeter in. This non-contact ammeter can be placed in the circuit at any place where current flows. Place the ammeter in the wire going to the bulb. • What is the value on the ammeter? • Place the ammeter in the wire going away from the bulb. Does this change the value of the current? Why do you think this might be? PART D: Resistors in Series, Parallel and Combination Pull three resistors from the Components section. Be aware that-the default value -of the resistors is 10?. Leave one with the default value and double click on the others to change/increase their values to 20? and 30?. Two clicks will increase resistor’s value from 10 ? to 20 ?, while three clicks will increase it from the default value of 10 ? to 30 ?, and so on…. Notice, that as you change the resistor value it changes the colored bands on the resistors. This is how we differentiate resistors when we use them. In any case, we will label the resistors from here on out as: Resistance #1 10? #2 20? 5 PHYS 100 – Simple Circuits #3 30? RESISTORS IN SERIES: Now connect the three resistors into a SERIES CIRCUIT with a single battery. Bring the Ammeter and Voltmeter onto the desktop. 1. Measure the voltage across each of the three resistors and record the values in the Series Table. 2. Measure the current in the wires going away from each of the resistors and record the values in the Series Table. 3. Use the Voltmeter to measure the voltage across the battery and the ammeter to measure the current coming from the battery. Record these values in the Series Table. SERIES TABLE 1 2 3 10 20 30 battery Voltage (V) Current (A) Resistance (?) Remember to show all your work and to answer to all listed questions. • What is the relationship between the current in each of the resistors and the current in the battery? • What is the relationship between the voltage across each of the resistors and the voltage from the battery? 6 PHYS 100 – Simple Circuits • Calculate the Total Resistance in the circuit using Ohm’s Law: ?? = ?? and the current (I) and voltage (??) from the battery. • If we added a 4th resistor to this circuit, would the value of the total resistance for the circuit increase, decrease or stay the same? Would the value of the current from the battery increase, decrease or stay the same? Would the value of the voltage from the battery increase, decrease or stay the same? RESISTORS IN PARALLEL Now connect the three resistors into a PARALLEL CIRCUIT with a single battery. Bring the Ammeter and Voltmeter onto the desktop. 1. Measure the voltage across each of the three resistors and record the values in the Parallel Table. 2. Measure the current in the wires going away from each of the resistors and record the values in the Parallel Table. 3. Use the Voltmeter to measure the voltage across the battery and the ammeter to measure the current coming from the battery (This is a bit tricky to do, even with a non-contact ammeter. You need to be sure to get ALL of the current coming from the battery). Record these values in the Parallel Table. PARALLEL TABLE 1 2 3 10 20 30 battery Voltage (V) Current (A) Resistance • (?) What is the relationship between the current in each of the resistors and the current in the battery? 7 PHYS 100 – Simple Circuits • What is the relationship between the voltage across each of the resistors and the voltage from the battery? • Calculate the Total Resistance in the circuit using Ohm’s Law: ?? = ?? and the current (I) and voltage (??) from the battery. • If we added a 4th resistor to this circuit, would the value of the total resistance for the circuit increase, decrease or stay the same? Would the value of the current from the battery increase, decrease or stay the same? Would the value of the voltage from the battery increase, decrease or stay the same? COMBINATION: RESISTORS IN COMBINATION Keep the very same numerical values of the three different electrical resistances onto the 3 electrical resistors, like before; check with the values in the table below and run the simulations with these specific values. + - R2 Now connect the three resistors into the Combination Circuit shown with a single battery. Bring the Ammeter and Voltmeter onto the desktop. R3 R1 1. Measure the voltage across each of the three resistors and record the values in the Combination Table. 2. Measure the current in the wires going away from each of the resistors and record the values in the Combination Table (Again, watch out for those resistors in parallel). 3. Use the Voltmeter to measure the voltage across the battery and the ammeter to measure the current coming from the battery. Record these values in the Combination Table. COMBINATION TABLE 1 2 3 battery 8 PHYS 100 – Simple Circuits Voltage (V) Current (A) Resistance (?) 10 20 30 Recall to answer to all listed questions. • Do the voltages and currents in your combination circuits follow the same rules as they did in your series and parallel circuits? If so, how so? If not, how not?