Blog - Week Three

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)

Figure 1:

Table 1:

Resistor Number	Measured Resistor Value
R1	4.69 KΩ
R2	3.3 KΩ
R3	0.89 KΩ

Figure 2:

 Table 3:

Resistor Number	Measured Resistor Value
R1	4.69 KΩ
R2	3.3 KΩ
R3	0.89 KΩ

Figure 2:

Table 3:

Resistor Number	Measured Resistor Value
R1	4.69 KΩ
R2	3.3 KΩ
R3	0.89 KΩ
R4	1.98  KΩ

Table 4:

Circuit	Calculated Resistance	Measured Resistance
A	0.6507 KΩ	0.650 KΩ
B	5.445 KΩ	5.44 KΩ
C	6.503 KΩ	6.490 KΩ

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



Table 4:

5V Applied to 120 Ω Resistor (Series)
Measured Current	Calculated Current
41.6 mA	41.0 mA

Table 5:

5V Applied to 120 Ω Resistor (Parallel)
Measured Current	Calculated Current
N/A	N/A

For the trial in parallel, the electricity could now take a path with a much smaller resistance, essentially shorting the circuit and providing us with little or no value and confusing the multi-meter.  

       The principal works for the same reason as it would if the multi-meter were just a resistor.  A series connection and a parallel connection are completely different.  For the series connection, the current will be 'shared' among the different components.  This value will remain constant but the voltage across each component will change.  For the parallel connection, there will be two separate paths in which the current can travel.  The voltage across each component, however, will remain the same.   

       The multi-meter is the same way.  In series with any component, the current will be constant.  Since the current comes through the same path, both components will read one current value.   But if one applies the same amount of current to the components with the multi-meter in parallel, there will be two separate paths in which that current can travel and likely two different currents.   Think of it based on Ohm's law (Voltage = Current * Resistance), the constant voltage will be divided by two different resistances and yield two different currents.  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)

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.



Table 6:

      

5V Applied to 120 Ω Resistor in Series with 47 Ω Resistor
	Measured	Calculated
R1 Current	29.9mA	29.0mA
R1 Voltage	1.40 V	1.405 V
R2 Current	29.9mA	29.0mA
R2 Voltage	3.49 V	3.588 V

          The results shown in table six are as expected.  The current measured through both objects in series are constant.  They are then operating as a voltage divider.   Ideally, the current passing through each component in series should be the same and the voltages should sum up to be equal to the Voltage Source.  In this case, the measured voltages of R1 and R2 add up to 4.89.  While this is close to the original 5V, this is not exact.   Causes of this could be human error in measurement, standards of error on equipment, extra resistance in the wires/bread board, or not quite getting 5V from the power supply.  

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.

Table 7:

5V Applied to 120 Ω Resistor in Parallel with 47 Ω Resistor
	Measured	Calculated
R1 Current (47 Ω)	92 mA	106 mA
R1 Voltage (47 Ω)	4.27 V	5V
R2 Current (120 Ω)	39 mA	47 mA
R2 Voltage (120 Ω)	4.27 V	5V

      Once again, the values in Table 7 don't quite add up to the ideal values from calculations, however, they are close.   Similarly to the previous example, this could be caused by human error, instrument tolerance, extra resistance in wires/breadboard, inconstant power or a combination of any of those things.  

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.

Table 8:

Voltage 1.2KΩ Horizontal	0.824 V
Voltage 1.2KΩ Vertical	0.685 V
Current 2KΩ	1.86 mA

           The circuit shown on the breadboard above in which the values are derived for table 8 is show below as Figure 4.  

Figure 4:

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

The equivalent resistance of the circuit shown in figure four is calculated to be 2.53 KΩ.

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

           When the power supply is on, we read a value of 0 KΩ.  When the power supply was off, we read value of 0.567 kΩ.   This is due to the way a multi-meter measures current. It applies a small test signal in order to evaluate the result and calculate a resistance.   Since there is a voltage now being applied to the circuit, there will be new voltages and currents effecting the returning value to the multi-meter.  This will force the multi-meter to make an incorrect calculation. 

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)

.

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

      In this case, the minimum and maximum voltage that can be obtained at V1 is 5V for both.  Since the potentiometer is in parallel with the source, as shown in the figure below, the only change that would if the resistance value provided by the potentiometer is adjusted is the current.    This can be explained by Ohm's law.  V/R = I .  The 5V is constant, yet the resistance is being manipulated.  That leaves the only variable left to change being the current.

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

 11. 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)

It's important to mention that the potentiometer cannot be turned to zero while in parallel with the power supply.  This will create a short circuit and likely fry the component.  

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

           Voltage divider also known as the potential divider. Using the voltage divider we are able to calculate the output voltage. Voltage divider is used on the two resistors in our circuit with values of 1K and 5K Ohms. The final calculation of the circuit will look like 5k/(1k+5k) multiplied by the 5V voltage source.. 

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

           Current divider is a simple linear circuit that produces the output current. By splitting the current between the branches of the divider. In our circuit we have the 1K and 5K resistors with the 5 voltage source. 

Blog sheet week 2

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

The A/B switch allows one to change which channel is being displayed on the information dials.  If both channels are set to be independent and have a voltage applied via their voltage control, they will both provide a voltage at the same time, regardless of what position the switch is in.  One could set up channel A for one desired voltage, switch to channel B for another desired voltage and then use both voltage sources simultaneously in a circuit application. 

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

The power supply can also regulate the current being provided on its channels.  It does so to ensure a constant supply of power. 

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

 The independent option allows for both channel A and B to have separate voltages that are not interaction with each other.  Changing the mode to tracking, however, will give the option to put the channels in series or parallel.  This allows for a greater difference in voltages.  In series the unit can output 48V at 0.5 A or in parallel the unit can output 24V at 1A.

Independent Mode

Series Tracking Mode

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

We are able to generate +30 V by using both A and B outputs in series and having the Positive and Negative leads in the positive and negative input on the power supply.

Positive 30 Volts

Positive 30 Volts Setup

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

In order to get a negative voltage, the positive and negative needs to be switched on the power supply

Negative 30 Volts Setup

Negative 30 Volts

Alternatively, we could have measured the voltage as  -30V by switching the positive and negative leads to the digital multi-meter.  We felt that the earlier method is best to stay organized for future use when a circuit may call for both positive and negative voltage.  

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

Positive 10 Volts

Negative 10 volts

Both positive and negative volts are setup using A and B channels. As long as you switch one of the channels with positive and negative leads it will create a negative voltage source. This is done by putting the power supply in independent mode. 

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)

Circuit Setup and Reading

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

The fuse for the Power Supply is located on the back under the power cord. The fuse is used to prevent any damage to the power supply in case anything would prevent the fuse to blow. If the fuse blows, the LED indicator will not light and the power supply will not operate.


9.Where is the fuse for the DMM? What is it for?
The housing for the fuse on the DMM is located on the back of the meter under the power cord. The correct fuse ratings for the DMM are 250mA fuse for 100Vac or 120Vac is selected, and 125mA fuse for 220Vac or 240Vac is selected.
  There is also a T2al 250V fuse on the front face that's duty is to make sure too much current is not passing through from the leads to the unit.

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

The accuracy on the 2 wire is slightly higher than the 4 wire on some measurements. For the 120 Ohm measurement the 2 wire accuracy is at .15% and the 4 wire is at .1%. The maximum input for the 2W resistor is 500V and the the maximum input for 4W resistor is at 250V.

 11.How would you measure current that is around 10 A using DMM?
In order to measure a current around 10A we would need to connect the lead cord to the 12A setting on the DMM. This would allow us to measure a current around 10 A using the DMM

Monday

1. What is the class format?

      The class format consists of quizzes, discussions, blog reports, midterms and a final exam. Monday will begin with a pre-quiz, lab intro and the start of the lab itself. During the Wednesday's class period we will continue the lab if it is not completed. Friday's class will have blog discussions and a post-quiz.

 2.What are the important safety rules?

 Everyone must know where the fire extinguisher, first aid kid, telephone and the list of emergency numbers. Every group must test if the equipment is working properly. When conducting the lab it is safest to power everything off when not working, ground the circuit and don't have wet hands. After you are done with the lab clean and tidy up your work station.
 

3.Does current kill?

 Yes when the amperes is between 0.1 and 0.2 it could cause death. Lower amperes will cause some pain and breathing troubles along with shock, muscular paralysis but this will not cause death.

 4.How do you read color codes?

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

 Tolerance is the percentage that the resister could be off. If the resistor has a 5% tolerance and a value of 470, the reading could be 5 percent higher or lower than 470.

 6.Prove all your resistors are within the tolerance range.

Given Resistors:                       Calculated Resistance

150 k-Ohm ±5%                       149 k-Ohms

1.5 k-Ohm±5%                         1.47k-Ohms

2.2 M-Ohm±5%                       2.22 M-Ohms

2.2 M-Ohm±5%                       2.22 M-Ohms

1.5 k-Ohm±5%                         1.47k-Ohms

120 Ohm±5%                           100 Ohms

820 k-Ohm±5%                        815 k-Ohms

47 Ohm±5%                             48.6 Ohms

821 Ohm±5%                           817 Ohms
2.72 k-Ohm±5%                       2.722 k-Ohms

Wednesday

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

Measuring the voltage we are able to get a value by putting the probes on the two ends of the what we are measuring, Calculating the current we will have to break up the circuit to get a current value.

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

Using the triple output dc power supply we are able to get 3 voltage values. One of the channels is a fixed 5 volts. The other two channels A and B are able to be changed from any voltage ranging from 0 volts to 24 volts.


3.

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

Ohm's Law is voltage equals the current multiplied by the resistance.  By getting the current and the voltage we are able to use this formula to get a resistance value.

5.                                                    Rube Goldberg

     Friday

   The circuit could be implemented in one of the middle stages of the Rube Goldberg machine by using a physical component to block the photo-resistor.   When the physical component was moved it would start the motor which could be attached to another component to start physical movement for the next stage of the Rube Goldberg machine.