Week 3

Blog sheet week 3

1.       Compare the calculated and measured equivalent resistance values between the nodes A and B for three circuit configurations given below. Choose your own resistors. (Table)

Image 1: Figure (a) shows three resistors in parallel. Figures (b) and (c) are a combination of series and parallel

Resistors used:

R1: 120 Ω

R2: 150 kΩ

R3:  41 Ω

R4: 360 Ω

Chart	Calculated Value	Measured Value
A	32.7 Ω	34.8 Ω
B	160.98 Ω	165.89 Ω
C	519.93 Ω	522 Ω

Our calculated values were fairly close to the measured values. We may have conducted minor mistakes in our calculations.

2.       Apply 5V on a 120 Ω resistor. Measure the current by putting the multimeter in series and parallel. Why are they different?

When measured in series, the current was measured at 39 mA and in parallel, the current was measured at 0.12 A. They're different because in parallel, the DMM will short out the circuit, thus not giving you an accurate reading.

3.       Apply 5 V to two resistors (47 Ω and 120 Ω) that are in series. Compare the measured and calculated values of voltage and current values on each resistor.

Our calculated & measured current values and voltage values were close to each other. The values are fairly close to each other because the two resistors are in series, meaning that the two would have similar current values. The only difference between the two resistors are the voltage values; in series, only the same current flows through the resistors, making the voltage values varying upon which resistor it flows through.

Resistors in Series:

Resistor Value	Measured Current	Calculated Current	Measured Voltage	Calculated Voltage
47 Ω	27 mA	29.94 mA	1.38 V	1.41 V
120 Ω	29.9 mA	29.93 mA	3.34 V	3.42 V

 4.       Apply 5 V to two resistors (47 Ω and 120 Ω) that are in parallel. Compare the measured and calculated values of voltage and current values on each resistor. 

Our measured and calculated current for the 47 Ω were off by 10.9 mA. We may have had a minor calculation error. The measured and calculated values for the current and voltage are different between each resistor because they're in parallel. When in parallel, the voltage is the same. However, the current through each resistor will be different, varying upon the resistor value. From the chart, the larger the resistor value is, the lower the current value will be.

Resistors in Parallel:

Resistor Value	Measured Current	Calculated Current	Measured Voltage	Calculated Voltage
47 Ω	99 mA	88.1 mA	5 V	5 V
120 Ω	38 mA	37.7 mA	5 V	4.8 V

 

5.       Compare the calculated and measured values of the following current and voltage for the circuit below: (breadboard photo)

a.       Current on 2 kΩ resistor,

b.      Voltage across both 1.2 kΩ resistors. 

Image 2: Our breadboard setup

In chart (a), Our calculated value was very close with the measured value. In chart (b), our calculated values and measured values were pretty close as well for the first 1.2 kΩ resistor, and slightly off for the second 1.2 kΩ resistor. The reason why the second resistor had a lower value than the first resistor is because they were in parallel; the voltage read across one resistor will not be the same as the next one. 

a.) 2 kΩ resistor

Calculated Value	Measured Value
1.80 mA	1.83 mA

       b.) 1.2 kΩ resistor 

Resistor	Calculated Value	Measured Value
1.2kΩ	1.21 V	1.27 V
1.2kΩ	0.5158 V	0.45 V

6.       What would be the equivalent resistance value of the circuit above (between the power supply nodes)?

The equivalent resistance value of the circuit is 2.176 k

7.       Measure the equivalent resistance with and without the 5 V power supply. Are they different? Why?

• The equivalent resistance with the 5V power supply was 25.26 MΩ. We weren't sure why we were getting such a high value, but something about it didn't seem right. We were expecting the value to be much lower.

• The equivalent resistance without the 5V power supply was 2.5 kΩ

They are different because of how the DMM measures the resistance; it supplies a current to the circuit and then measures a voltage. If an outside voltage source is added, it should throw off the measurement.

8.       Explain the operation of a potentiometer by measuring the resistance values between the terminals (there are 3 terminals, so there would be 3 combinations). (video)

A potentiometer operates by spinning its dial to either increase or decrease the resistance value. The video below provides a more detailed explanation.

 Video 1: Explanation of the potentiometer

Lead Combination	Value
1 and 2	5.3 k Ω
2 and 3	5.3 k Ω
1 and 3	1.3 k Ω

9.       What would be the minimum and maximum voltage that can be obtained at V1 by changing the knob position of the 5 KΩ pot? Explain.

The maximum would be 5V because if the knob on the pot is almost turned all the way up, you’ll get close to 5V.

The minimum would be 0V because the knob on the pot is almost turned all the way down, you’ll get close to 0 V.

10.   How are V1 and V2 related and how do they change with the position of the knob of the pot? (video)

Video 2: Showing how the knob affects the DMM readings

(Note: Our leads were switched, hence the negative reading)

V1 is constantly set at 5V because there’s no other component between that and the voltage source. V2 would be different because of the 1k resistor. They are related by:

 (R2/R1+R2) *V1 = V2

11. For the circuit shown in the video below, you should NOT turn down the potentiometer all the way down to reach 0 Ω. Why?

If you turn the potentiometer all the way down to reach 0 Ω, it will short the voltage source, thus creating high current and it will destroy the potentiometer. 

 12.   How are current values of 1 kΩ resistor and 5 kΩ pot related and how do they change with the position of the knob of the pot? (video)

Video 3: Showing how current values change according to the knob's position 

The current would be the same because it’s in parallel if it’s at 1k. If the pot increases resistance, current should decrease; as the pot decreases, the current should increase.

13.   Explain what a voltage divider is and how it works based on your experiments.

A voltage divider is a series of resistors or capacitors and an input that turns larger voltage into a smaller one. It can produce a specific output voltage, which is a fraction of the input voltage. From our experiment, we used the potentiometer to adjust the voltage. By turning the knob either left or right, the resistant value is adjusted; either increasing the voltage or decreasing the voltage of the output.

14.   Explain what a current divider is and how it works based on your experiments.

A current divider is a group of resistors connected in parallel and divides the current from the power source. This allows different amount of current to be allocated to different parts of a circuit. In our experiment, it's based on the resistor value. As the potentiometer's resistance decreased, more current goes through it, causing less to travel through the 1k resistor.

Week 2

Wednesday: 

1.       What is the role of A/B switch? If you are on A, would B still give you a voltage?

The role of the A/B switch is to signify which supply the V and mA meters are connected. If you’re on A, B would still give you a voltage; it doesn’t matter if it’s on independent or tracking.

2.       In each channel, there is a current specification (either 0.5 A or 4 A). What does that mean?

      This means that there is an adjustable power supply from 0-24 V, hence up to 0.5 A, and a fixed 5 V supply up to 4 A. The current specification allows the Constant Current indicator to light if there is a unit that doesn’t meet the specification and can be rejected.

3.       Your power supply has two main operation modes for A and B channels; independent and tracking. How do those operation work? (Video)

Video 1: Using the power supply to see the differences of switching from

different modes for A and B

In independent mode, A and B each supply 0-24 V up to 0.5 A. The operating controls for the two are independent of each other and can be use either individually or simultaneously.

In tracking mode, the B supply tracks the voltage the A supply. It can be used in series or parallel. In series, A and B supplies are connected in series, which allows a single output of 0-48 V at up to 0.5 A. In parallel, A and B supplies are in parallel and allows a single output of 0-24 V at up to 1 A.

4.       Can you generate +30 V using a combination of the power supply outputs? How? (Photo) 

      Yes, you can generate +30V by having A and B in series tracking mode. If the voltage for A is set to 15 V, then the output voltage should be 30 V.

Image 1: Multimeter measured at 37.36 V

5.       Can you generate -30 V using a combination of the power supply outputs? How? (Photo)

Yes, if you flip around the prongs to get the opposite reading. You can also obtain -30 V by grounding the positive terminal of A and the positive lead of A should be connected into the negative terminal of B.

Image 2: Multimeter measured at -30.64 V

6.       Can you generate +10 V and -10 V at the same time using a combination of the power supply outputs? How? (Photo)

       

      Yes, by having both A and B supplies are set to 10 V in independent mode and by having the power supply wired in series. The positive and negative lead are connected opposite from each other; being said, connecting the red wire to the second power supply gives you 10 V while connecting the red wire to the negative terminal gives you -10 V.  Pictures are provided below. 

Image 3: First value measured: +10 V

Image 4: Second value measured: -10 V

Image 5: Our setup to show how to get +10 V and -10 V at the same time on the DMM

7.       Apply 5V to a 100 Ω resistor and measure the current by using the DMM (remember the setup in DC 3). Compare the reading with the current meter reading on the power supply. At what angle of the current knob makes the LED light on? If you keep on decreasing the current limit, what happens to the voltage and current? (Video)

On the power supply, we measured 20 mA and on the DMM, we measured 44.83 mA. The angle of the current knob that makes the LED light on is a little over 180 degrees. If you keep decreasing the current limit, the voltage and current both decrease; obtaining a negative current value at one point.

If it’s fixed, the current shows at 0 mA.

                             Video 2: Our setup to see what the maximum current value is                   

                                                   (the light turns on if it reaches over maximum)

8.       Where is the fuse for the power supply? What is it for?

      The fuse for the power supply is located on the back of the power supply. It is used to prevent the power supply from being damaged if it is overloaded.

9.       Where is the fuse for the DMM? What is it for?

The fuse for the DMM is on the bottom left hand corner. It’s for breaking the circuit if a current exceeds a safe level.

10.   What is the difference between 2W and 4W resistor measurements?

The difference between a 2W resistor and a 4W resistor is that the 2W resistor allows a maximum of 500 V dc or ac rms while the 4W resistor allows a maximum of 250 V dc or ac rms. The 4W resistor is also more accurate than the 2W resistor.

11.   How would you measure current that is around 10 A using DMM?

      Using the DMM, you would measure the current by placing the positive lead beneath the negative. Our picture shows 0 mA because we didn't meet the requirements at 4W.

Image 6: Showing how where the leads are placed on the DMM

Week 1

Monday:

1.       What is the class format?

The majority of the class format involves labs, blogs, quizzes, and exams. There are a total of 30 quizzes worth 10 points each; 15 discussions worth 10 points each; 15 blog reports worth 20 points each; 2 midterms worth 50 points each; and one final exam worth 150 points. The main goal for each student is to get as many points possible for a high grade.

2.       What are the important safety rules?

a.       Don’t work alone on energized electrical equipment

b.      Power must be turned off during assembly and disassembling. Discharge any high voltage points to ground

c.       Make measurements in live circuits with well insulated probes and one hand behind your back. Don’t allow any part of your body to touch any part of the circuit or equipment connected to the circuit

d.      Don’t touch electrical equipment while standing on wet floor or metal floor

e.      Don’t handle wet, damp, or ungrounded electrical equipment

f.        Jewelry such as rings and watches can be hazardous

g.       Don’t try to catch a falling part of a live circuit

h.      Don’t touch two pieces of equipment simultaneously

i.         Don’t touch even one wire of a circuit; it may be “hot”

j.        Avoid heat surfaces

k.       Be cautious when handling components

l.         Ask instructor to check your circuit before applying power

3.       Does current kill?

Yes

4.       How do you read color codes? (Video)

5.       What is the tolerance? Give an example from your experiment.

      Tolerance is the variance of a resistor. We read the bands on the resistor to determine its theoretical value and then used the multimeter to determine its actual value to compare them. 

6.       Prove all your resistors are within the tolerance range

Theoretical	Actual	Tolerance: Y/N
2.72 k Ω	2.71 k Ω	Y
15 k Ω	14.9 k Ω	Y
2.2 M Ω	2.2 M Ω	Y
150 k Ω	147.5 k Ω	Y
8.2 M Ω	8.36 M Ω	Y
360 Ω	358 Ω	Y
47 Ω	47.5 Ω	Y
15 k Ω	1.479 k Ω	Y
121 Ω	119 Ω	Y
8210 Ω	816 k Ω	N

Wednesday:

1.       What is the difference between measuring the voltage and current using a DMM? Why?

The difference between measuring the voltage and current using a DMM depends on where you plug in the cords on the DMM and which settings you’re using. To measure the current, you have to break the loop whereas for voltage, you don’t.

2.       How many different voltage values can you get from the power supply? Can each one of them be changed to any value?

You can get three different values; one is fixed and the other two can range anywhere from 0 V to 25 V.

3.       Practice circuit results (video) & (photo)

4.       How do you experimentally prove Ohm’s Law? Provide measurement results. Compare calculated and measured voltage, current, and resistance values. (Experimental setup photo)

We measured the voltage and current using the DMM and they should be linearly dependent. As voltage increases, current increases. We used a 100 Ω resistor and a 150 k Ω resistor. The chart below summarizes our findings after conducting five trials for each resistor. The larger the resistor value is, the more/less the current is at a fixed voltage

100 Ω Resistor

Trial	Voltage Measured	Ampere Measured
1	2.69 V	24.4 mA
2	3.51 V	31.2 mA
3	6.16 V	55.1 mA
4	6.81 V	60.8 mA
5	7.24 V	65.5 mA

150 kΩ Resistor

Trial	Voltage Measured	Ampere Measured
1	2.06 V	0.0143 mA
2	2.83 V	0.0196 mA
3	3.81 V	0.0259 mA
4	4.29 V	0.0295 mA
5	5.02 V	0.0343 mA

5.       Rube Goldberg circuit (video).

Friday:

1.       Draw the circuit diagram for the Rube Goldberg set-up.

2.       How can you implement this setup into a Rube Goldberg machine? Drawing required.

We could use the motor to start a new chain of reaction. Our current idea is to create a pulley system by using a photo sensor and a motor. By shining a light on the photo sensor the motor will begin to turn. Around the motor is a string that will lift up the flags.