**Instructions**

1. Include units with your answers when needed. 2. Explain your answers (Just yes or no is not enough) 3. Type your answers in the yellow shaded spaces and complete the data tables. 4. Do NOT alter the worksheet (change the font, font size, yellow shaded spaces etc.) and the formatting 5. Include calculations of all your work. 6. Save the file with doc, docx or PDF extension and submit it.

**Objectives**

When you have completed this assignment, you will be able to:

- Use an ammeter and voltmeter to take readings in circuits.
- Use Ohm’s Law to determine the relationship between Current, voltage and resistance.
- Connect resistors in series and parallel.
- Measure the current and voltage in series and parallel circuits.
- Compute equivalent circuit resistance and verify the rules for combining resistors in series and parallel.

** Equipment**

Computer with internet, Word processing software ( MS Word).

** Procedure:**

** Part I: Ohms law [ 34 points]**

** Click here to launch the simulation**

Click the above link or search PhET HTML5 and select – *Circuit Construction Kit: DC – Virtual lab*

The simulation has a component selection pane on the left with various circuit components such as wires, batteries and bulbs. On the right side is an *ammeter* to measure current and a *voltmeter* to measure voltage. Below that is a battery shown pictorially and as an electric symbol. The circuit components can be viewed pictorially or as symbols by selecting one of these two. The convention in circuit analysis is for current to flow out of the positive terminal of the battery and into the negative terminal of the battery. In actuality, the flow of electrons is the opposite of this. On the top right of the screen you can select to see the flow of current. The relationship between current (I), voltage (V), and resistance (R) is given by Ohm’s Law . Resistance value of components can be edited by a tap on the component.

1. Build the circuit in figure1below. Grab the items from the left side of the screen. Select ‘Labels’ and ‘Values’. Click on show current to see the current flow.

Let’s start with a **simple circuit. A** 9v battery is connected to a resistor (10 Ω) through a switch. A voltmeter can be used to measure the *voltage across* any component in the circuit as shown. Tap the battery to edit voltage. Tap the resistance to change the resistance. Resistance and voltage value of components can be edited by a tap on the component and using the slider control at the bottom of the screen

*Figure 1. Simple circuit*

What do you expect the voltage across the **resistor** to be? *[ 2 points]*

2. Construct the circuit in figure 1 and measure the voltage across the resistor. *[ 2 points]*

V=

3.Tap on the resistor and change the resistance to 20 Ω. Now measure the voltage across the resistor. Explain why the value is the same/different compared to #2. *[ 2 points]*

V=

4. Change the voltage of the battery to a value that makes sense for your circuit (Tap the battery to edit voltage. Use the slider control at the bottom of the screen). What would the voltage across the resistor be? Explain. *[ 2 points]*

- Return the resistance value back to 10Ω so that the circuit looks like figure 1 again. Now what is the
*current*flowing through this circuit? Calculate it using Ohm’s law. Show calculation below (Remove the wire between terminals A and B and*connect the ammeter*between those two points and check your answer.)*[ 4 points]*

I =

*[ Work]*

- If the battery polarity is reversed will anything change in the circuit? Tap the battery and flip the polarity of the battery .

Select ‘**Show Current’** on the top right and observe the flow. Return the battery polarity to the original orientation and observe the current flow again. What do you notice? *[ 2 points]*

7. Construct a circuit like fig.1. Tap on the battery to change the potential difference of the battery. Record the potential difference (start with 5V) and the current flowing through the circuit in Data Table 1 below. Change the potential difference across the battery four more times. Record the current and the potential difference in the data table after each change.

**Data Table 1** *[ 10 points]*

Potential Difference (V) | Current (A) |

8.Construct a graph (Using excel) of V(y axis) vs I (x axis) and find its slope.

Click here to How to Find the Slope Using Excel

Click here to find how to add axis titles to a chart

**NOTE on Graphing**

If both the links are not helpful, please search online how to make a graph on Excel. Here is a search result.

** How to make a graph using Excel 2010 version** (other versions and software should be fairly similar) In the “Insert” menu tab, choose “Scatter Chart” – “scatter with markers only.” Click on “Select Data.” In the pop-up window, click the “Add” button. In the pop-up window for “Series X values, click on the blue and red mini box at the end of the data entry cell, and highlight the desired cells for graphing. For Data Table 2, highlight the t1 through t9 cells. Click on the blue and red box at the end of the data entry cell. Repeat for “Series Y values”, using x1 through x9 cells. Click “OK.” This returns you to the “Select Data Source” window. Click “OK.” To get a Trendline, click on any data point, and choose “Add Trendline…” from the drop-down menu. Choose “Linear,” and check “Set Intercept” and “Display Equation on chart.”

You can also make a graph on a graph paper.

Insert your graph here. (It should have an appropriate title. The axes should be labeled, and the units should be indicated. The data points should be marked. The slope equation should be shown). *[ 5 points]*

* [ Graph]*

9. Record your slope here. What quantity does slope represent? *[ 3 points]*

10.Find the percent error between your experimental R value(slope) and true ‘R’( the one in the simulation) value. Show all your work. *[ 2 points]*

% Error = (100%) • (│Your Experimental Result – True value │/ True value)

Part 2 Resistors in series *[Total 38 points]*

11.Connect two 10 Ω resistors in **series **with a 9V battery as shown in figure 2.

*Figure 2 Series circuit*

12. Using the voltmeter measure voltages: *[ 6 points]*

V_{AC}= ________ V_{AB }= __________ V_{BC} = __________

13.So how has the voltage across the 10-ohm resistor changed when in a simple circuit (Fig 1. Question 2) to when in a series circuit ( Figure 2 Question 12 , V_{AB}) using the same battery voltage? *[ 2 points]*

14.What is the effective resistance (R_{series } ) in the series circuit?

You know the battery voltage, so using Ohm’s law calculate the current I through the circuit.

Show all your work including formula. *[ 4 points]*

15. What is the current through the resistor one ?

What is the current through the resistor two? Explain your answer.

* (Check your answers by dragging the current meter from the right side of the screen. Place the cross hair in the circuit to read current. Or you can read the current by connecting the ammeter first at the negative terminal of the battery, and then at terminal C, and finally between B&C.)* *[ 4 points]*

16. Next connect 3 resistors in series as shown in figure 3.

*Figure 3. Three similar resistors in series*

17. Record the *voltage* across each resistor using voltmeter. *[ 6 points]*

V_{R1} = V_{R2} = V_{R3} =

18. Record the *current* in the circuit using ammeter.* [ 2 points]*

19.Show your calculation for (include your work and all the formulas)* [ 6 points]*

- total resistance of the circuit

- voltage across each resistor

c) Current in the circuit and current through each resistor.

20. Using #5, 15, and 19, fill in table 2.

**Table 2 ** *[ 6 points]*

Simple circuit | Series circuit | Series circuit (3 resistors) | |

Circuit Resistance | |||

Circuit Current |

21.Explain in your words how current and circuit resistance values change as you go from a simple circuit to series circuit of increasing resistors, using table 2. *[ 2 points]*

**PART 3. Resistors in Parallel ***[ Total 28 points]*

Construct a circuit as shown in figure 4.

*Figure 4. resistors in parallel*

22. Connect two resistors in parallel with a 9V battery as shown in figure 4. Measure the voltage across each resistor. *[ 4 points]*

V_{R1} = V_{R2} =

23. If the battery was changed to say a 12v battery, then how will the voltages change across each resistor? Record the new values. Explain your answer. *[ 4 points]*

V_{R1} = V_{R2} =

24.You know the voltage across R_{1 }in fig 4, and the resistance value, use Ohm’s law to find

the current through R_{1 }and R_{2}.* [ 4 points]*

I_{R1} = I_{R2} =

*Figure 5. resistors in parallel*

25.Now, what is the battery current in the parallel circuit is ( hint:I_{R1+ }I_{R2 }). *[ 4 points]*

Confirm this value by connecting the ammeter next to the battery as shown in fig.5. *[ 4 points]*

Ammeter Reading =

26.Compare this current with the current in the series circuit #15 and the simple circuit #5. Fill in values in the table 3 for current and resistance

**Table **3*[ 6 points]*

Simple | Series | Parallel | |

Battery current | |||

Circuit Resistance |

22.What do you think the resistance of the parallel circuit will be? Choose the correct answer.* [ 2 points]*

- greater than the simple circuit but less than the series circuit
- greater than the simple circuit and greater than the series circuit

- less than the simple circuit and less than the series circuit

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