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?The resistors are: 101 ohm, 47 ohm, 1.2 K ohm, and 47 ohm.
Group

Measured
(ohms)

Calculated
(ohms)

A

32

31.3

B

146.3

145.6

C

77.5

79.4

Table 1. Calculated and measured value for resistor combinations
2. Apply 5V on a 120 Ω resistor. Measure the current by putting the multimeter in series and parallel. Why are they different?
in series we got 39.8 mA, in the parallel we cannot measure the current because the current here is so high, and the resistance is like 0+ and V/0+ gave an infinity.
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?
Resistor(ohm)

Calculated
Voltage(V)

Measured
Voltage(V)

Calculated
Current(mA)

Measured
Current(mA)

47

1.4

1.43

29.94

28.98

120

3.6

3.64

29.94

28.98

Table 2. Calculated and measured values for 47Ohm and 120Ohm Resistors
The measured and calculated value for voltage and current are so close. The current for both resistors is the same because they are in series.
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?
Resistor(ohm)

Calculated
Voltage(V)

Measured
Voltage(V)

Calculated
Current(mA)

Measured
Current(mA)

47

5

5.03

97

90

120

5

5.03

42.23

39.9

table 3. Calculated
and measured values for 47Ohm and 120Ohm Resistors
The measured and calculated value for voltage and current are so close. the voltage across the two resistor are the same because they are in parallel but the current is different.
a. Current on 2 kΩ resistor.
Measured is 1.94 mA, Calculated is 1.9993
b. Voltage across both 1.2 kΩ resistors.
For R1=1.2kΩ, Calculated voltage = 0.84V, Measured voltage = 0.859V.
For R2=1.2kΩ, Calculated voltage = 0.689V, Measured voltage = 0.705V
6. What would be the equivalent resistance value of the circuit above (between the power supply nodes)?
Equiv. Res. = 2520 Ohms
7. Measure the equivalent resistance with and without the 5 V power supply. Are they different? Why?
The equivalent resistance without power is 2.62 k Ohms, and you can't measure it with the power on. You can't measure the Eq. Re when the power is on because there is a current flowing through the circuit and it'll measure the current or the voltage, but not the resistance.
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)
The potentiometer changes the resistance values when the pins are set in different orders. The combination of (A/C)/(B/C) had minimum readings, and then (A/B) had the highest reading.
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 minimum voltage would be 0 Volts and the maximum voltage would be 5 Volts. 0 Volts comes from max resistance and 5 V comes from no resistance.
10. How are V1 and V2 (voltages are defined with respect to ground) related and how do they change with the position of the knob of the pot? (video)
V2 is always lower than V1. When V1 goes lower, V2 goes lower because it is always in respect to the input voltage of V1.
11. For the circuit below, YOU SHOULD NOT turn down the potentiometer all the way down to reach 0 Ω. Why?
Turning down the potentiometer all the way down to zero acts like you are dividing the voltage by 0+, and will short the circuit because too much current will be flowing through the circuit.
12. For the circuit above, 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).
When the resistor was 1K Ohm, the current was 5mA, and when the Resistor was 5K Ohm, the current was 1mA. This is because there are 5 Volts flowing through the circuit, so it needs to be the same with the current/resistance change. It has to add up to 5 Volts.
13. Explain what a voltage divider is and how it works based on your experiments.
A voltage divider turns large voltage into smaller voltage. Using two resistors in series, the output voltage is much smaller than the input.
14. Explain what a current divider is and how it works based on your experiments.
A current divider creates an output current that is much smaller than the input current. You use one with two resistors in series.
Blog looks like its coming along well. I was looking over the information, and I don't see anything wrong with the calculations or anything. Other than number 2. Number 2 gave us difficulty as well. However, I am curious to high high the current actually was. The DMM hand held or the one thats up on the shelf. They both can measure up 10 A. I don't think power supply can even supply that much current, nor do I want it to, that's a little scary. If I were you guys, it might be good to go back and look at that one again! Good work so far!
ReplyDeleteIt is looking really good so far. Something that stands out is your tables, they really make your blog stand out. How was your number 5? I know for ours that caused a little bit of trouble. Calculating the first resistor was easy but when we were measuring we were getting two different values to start. Eventually we got it, but at first it was hard. Very good job though! make sure to finish.
ReplyDeleteFor number 2 the currents are different because when measured in parallel, the DMM shorts the resistor and because of this the current is incorrect because it isn't taking into account the change in current due to the resistor. To get the proper reading you measure current in series. We also had a different answer than you on number 7. We thought that you couldn't get a measurement with the power supply on because the voltage of the DMM and the Powersupply interfere with each other when measuring resistance. Other than these differences, our results were quite similar. Keep up the good work and good job this week!
ReplyDeleteI believe for the last question asking about current dividers, your resistors would have to be in parallel not series. Remembering back to Circuits 1, current is constant in a single loop and the input current only divides when there is another loop in the form of a parallel circuit. I will include a link that can hopefully explain better than I.
ReplyDeletehttps://en.wikipedia.org/wiki/Current_divider
Our values to question number 4 were about as accurate as your guys but I cant think of any reasons for that great of an inaccuracy other than the measurements of the resistors being measured using a 2W format as opposed to a 4W. Do you guys have any other thoughts on what may have possibly caused these errors for both of us?
ReplyDelete2, 7, 8, 10, 12, 13, 14: Explanations not correct or satisfactory.
ReplyDeleteNo responses to other comments.
Use captions for videos as well next time (no point deduction).
"A voltage divider is a simple circuit which turns a large voltage into a smaller one." is plagiarism! NEVER AGAIN!
ReplyDelete