## Friday, January 29, 2016

### Lab 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)

R1: 2.2 Mega Ohms  R2: 100 Ohms  R3:  47 Ohms  R4:  150 Kilo Ohms

 Calculated Measured a) 31.9723 Ω 31.601 Ω b) 2.20003 Ω 2.255 MΩ c) 2.2001 MΩ 2.256 MΩ

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

The measured current was 39.18 mA while the multimeter was in series.  When we put the multimeter in parallel the current takes the path of least resistance around the resistor, thus overloading the multimeter.

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.

 Calculated Values Measured Values V(120 Ω) = 3.59 V V(120 Ω) = 3.62 V V(47 Ω) = 1.407 V V(47 Ω) = 1.416 V I(120 Ω) =  29.94 mA I(120 Ω) =  29.9 mA I(47 Ω) =  29.94 mA I(47 Ω) =  29.9 mA

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.

 Calculated Values Measured Values V(120 Ω) = 5 V V(120 Ω) =  5 V V(47 Ω) =5 V V(47 Ω) =  5 V I(120 Ω) = 32.516 mA I(120 Ω) = 39.13 mA I(47 Ω) =  106.38 mA I(47 Ω) =  89.45 mA

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

 An image of our circuit for Q5.

a. Current on 2 kilo Ohm resistor.

We calculated a current of 2.5 mA on the 2 Ohm resistor and measured a current of 2.28 mA.

b. Voltage across both 1.2 kilo Ohm resistors.

 Calculated Values Measured Values #1 1.2kΩ .8328 V .8527 V #2 1.2kΩ .7038 V .7224 V Both 1.5094 V 1.58 V

6. What would be the equivalent resistance of the circuit above?

The equivalent resistance of the circuit above is 2.523 kilo Ohms.

7. Measure the equivalent resistance across the circuit above with and without the power supply.   Are they different?  Why?

The measured resistance across the circuit without the power supply is 2.254 kΩ.
The measured resistance across the circuit with the power supply is OL.
They are different because the digital multimeter uses a small current to measure the resistance of the resistor, and when you apply a voltage to a resistor you are trying to measure the multimeter can't measure the resistance because it doesn't know what other voltage/current is being applied.

8. Explain the operation of a Pentiometer by measuring resistance values between the terminals.

A video explaining the operation of a potentiometer.

9.  What is the minimum and maximum voltage values that can be obtained at the potentiometer by changing the knob on the pot?

The minimum voltage obtained is .1 mV and the maximum voltage that can be obtained is 5 V.  As the resistance of the pot goes up the voltage allowed through gets to be less and less.

10.  How are the voltages of two resistors related and how do they change as the pots knob is moved?

A video showing the voltage across the first resistor.

A video showing the voltage across the potentiometer.

11.  How are the current values of the 1k resistor and the 5k potentiometer related and how do they change with the position of the knob?

A video showing the current through the potentiometer.

A video showing the current through the 1k resistor as the potentiometer is adjusted.

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

A voltage divider is a simple circuit which turns a large voltage into a smaller voltage.  A potentiometer is a variable resistor which can be used to create an adjustable voltage divider.  Inside there is a single resistor and a wiper which cuts the resistor in two.  It moves to adjust the ratio between both halves.

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

A current divider circuit in which the main current from the power source is divided up among the circuit.  Different amounts of current are allocated to different parts of the circuit.  The potentiometer from the circuit in number 11 adjusted the resistance of the circuit and depending on the resistance is higher than the 1K resistor the current will follow the path of least resistance.

## Thursday, January 21, 2016

### Lab 2

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 tells the V meter and mA meter of the power supply to either show the current and voltage of the A or B channel. Regardless of the position of the switch there is voltage being applied to both channels.

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

The fixed 5V supply can provide a 0-4 amp current depending how much the circuit requires. The two supplies labeled “A” and “B” are the 0-24 Volt supplies. They continuously supply voltage within that range and each has a 0.5 amp current capacity.

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

When the power supply is on independent operation mode, which is when the button is all the way to the right, the “A” and “B” power supplies are completely independent from one another. Tracking mode can be in positions Parallel or Series. When the switch is in the middle position it is in Parallel tracking and the “A” and “B” supplies are wired together. The current and voltage can be adjusted using the “A” controls. The two controls can also be used independently, but somewhat follow one another, also known as tracking. The output can be used as a 0-24 volt supply with a 1 amp capability. When the switch is the left position the power supply is in Series tracking mode. In this setting the “A” controls are used for the maximum voltage of both supplies. In this mode the voltage terminals at “B” supply tracks the voltage on the “A” supply. The positive terminal of “B” is also internally connected to the negative terminal of “A” supply which allows the two supplies to be used as one 0-48 volt supply.

Here are two videos explaining the differences between the switch positions.

Video 1:
A video containing the first half of a 51 second clip showing the differences between switch positions.

Video 2:
A video showing the second half of a 51 second clip showing the differences between switch positions.

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

Yes, the power supply must be in series mode and your ground probe should be in negative slot on the B supply and the positive probe should be in the positive slot on the A supply.

 A picture of +30V output and the connections used to obtain it.

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

Yes, the power supply should be in series mode and your ground probe should be in the positive slot on the A supply and the positive probe should be in the negative slot on the B supply.
 A picture of -30V output and the connections used to obtain it.

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

Yes, you can get +10v and -10v at the same time.  What you need to do is connect two power supplies in series at 10V each so you have a total of 20V.  When you measure you ground the DMM in between the two power supplies, at the positive terminal of the first power supply.  To measure the to get +10V you connect the red wire to the positive terminal of the second power supply and to get -10V you connect the red wire to the negative terminal of the second power supply.

 A picture of +10.29V output and the connections used to obtain it.

 A picture of -10.29V output and the connections used to obtain it.

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 DMM we have a reading of 2.5 micro amps and on the power supply we have a reading of 30 mA.  When the current knob indicator is approximately 45 degrees from 0 setting the LED indicator light turns on.  When you hit 45 degrees from the minimum the voltage and current decrease with each additional degree you move the knob.

A video showing the angle at which the LED light comes on.

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

The fuse for the power supply is located on the back below the power cord connections.  The fuse is there to ensure the equipment is not damaged in case of an overload in current.

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

The fuse for the DMM used in class is located on the back below the power cord connector. The purpose of the fuse is to protect the equipment in case of an overload in current.

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

98.058 4W measurement
97.843 2W measurement

2W stands for 2-wire resistance measurements and can get good measurements at higher resistances. 4W stands for 4-wire resistance measurements and is often used to measure lower resistance values.

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

You would plug the positive terminal into the bottom right connection on the front of the DMM and the negative terminal into the original slot.  You then use the up arrow to select the amps measurement.

## Friday, January 15, 2016

### Lab 1

Week 1

Monday:

1.       What is the class format?  Each week will start with a pre-quiz, then a lab intro followed by working on the lab through Wednesday.  Friday includes blog discussions and the post-lab quiz.

2.       What are the important safety rules?  Never work with wet hands.  Power must be switched off when an experiment is being handled.  Do not work along with energized electrical equipment.  Know where the fire extinguisher, med kit, and phone are in case of emergencies.

3.       Does current kill? Yes, about .2 amps can kill.

4.       How do you read color codes? (Video)
You read color codes left right.  For example if you have black, red, orange, red, then gold you have 0, 2, 3, x100 ohms, and 5% tolerance.  That means you have 2300 ohms resistance with a 5% plus or minus tolerance.

5.       What is the tolerance? Give an example from your experiment.  Tolerance is the expected level of range in measured values of a resistor.

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

 Resister Band Value (Ω) Range (Ω) Tolerance Measured Value (Ω) 150k 142.5k - 157.5k 5% 147.6k 27.2 24.48 - 29.92 10% 2.71k 360 342 - 378 5% 358 120 114 - 126 5% 119 1.5k 1.425k - 1.575k 5% 1.48k 98.1k 88.29k - 107.91k 10% .816k 42 39.9 - 44.1 5% 46.3 2200k 2.09M - 2.31M 5% 2.258M 25k 23.75k - 26.25k 5% 14.94k 820k 779k - 861k 5% 816k

Wednesday:

1.       What is the difference between measuring the voltage and current using a DMM? Why?  You connect the positive probe to the upper right for voltage and resistance.  For amperage you connect the positive probe to the left of the ground.  When you measure voltage you connect to measuring alligator clips on both sides of the resistor, but when you are measuring the current you need to break the circuit to make the multi-meter part of the circuit.

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 any value for voltage from 0 to 25 on A and B on the power supply.  On the unchangeable connection the voltage is at a constant 5V all the time, it cannot be changed.

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

How do you experimentally prove Ohm’s Law?
You experimentally prove Ohm’s law by taking a resistor of known value, providing a voltage of known value, and measuring the current to see if it falls within the predicted range depending on the tolerance of the resistor.  Provide measurement results.
 Register Band Value (Ω) Range (Ω) Tolerance Measured Voltage (V) Measured Current (mA) Calculated Resistance (Ω) 360 342 - 378 5% 1.05 2.84 369.718 360 342 - 378 5% 2.07 5.57 371.634 360 342 - 378 5% 2.53 6.81 371.512 360 342 - 378 5% 3.4 9.19 369.967 360 342 - 378 5% 4.05 10.93 370.54 100.2 95.19 - 105.21 5% 5 43.28 115.527 100.2 95.19 - 105.21 5% 4 34.38 116.347 100.2 95.19 - 105.21 5% 6.02 52.52 114.623 100.2 95.19 - 105.21 5% 8.35 72.8 114.698 100.2 95.19 - 105.21 5% 12.65 124.58 101.541

4.        Compare calculated and measured voltage, current, and resistance values. (Experimental   setup photo)

5.       Rube Goldberg circuit (video).

Friday:

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

How can you implement this setup into a Rube Goldberg machine? Drawing required.
If you have some solar panels to charge a battery, a light sensor could be used to open the garage door if/when there is a power outage in your area.

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