Monday, January 25, 2016

Week 3, 1/25-1/29:

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) Picture 1 are the circuits that we had to build.

Picture 1

We chose resistors all equal to 120Ω and then calculated what the total resistance should be. After calculating we build the circuit and then measured using a DMM to double check our work. A table of our measurements is below.

Circuit	Calculated Resistance	Measured Resistance
A	40Ω	39.8Ω
B	180Ω	178.1Ω
C	200Ω	197.4Ω

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

When in parallel we get 0mA and when in series we get roughly 41mA. This is due to needing to have to break the circuit to measure the current. When the probe is in parallel with the resistor, it will short the circuit resistor. So no current flow can be measured through the resistor.

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.

The resistors in series will make an equivalent resistance of 167Ω. Using this resistance we calculated the voltage and resistance and current and then measured each. The 120Ω resistor was placed before the 47Ω resistor. A table of our results is below.

Resistor (Ω)	Calculated Current (mA)	Measured Current (mA)	Calculated Voltage (V)	Measured Voltage (V)
47	33.4	29.5	1.39	1.44
120	33.4	29.5	3.54	3.74

  

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. 

The resistors in parallel with make an equivalent resistance of roughly 33.77Ω. Using each resistor we calculated the voltage and current and then measured each. A table of our results is below.

Resistor (Ω)	Calculated Current (mA)	Measured Current (mA)	Calculated Voltage (V)	Measured Voltage (V)
47	108.51	97.10	5	5.10
120	42.75	41.40	5	5.10

5. Compare the calculated and measured values of the following current and voltage for the circuit below: (breadboard photo) Picture 2 is the circuit we had to build. Picture 3 is what we built.

a. Current on 2 kΩ resistor,  

Resistor(Ω)	Measured current(mA)	Calculated Current(mA)
2k	2.03	1.98

b. Voltage across both 1.2 kΩ resistors.

Resistor(kΩ)	Measured Voltage(V)	Calculated Voltage(V)
1.2(1)	0.72	0.70
1.2(2)	0.85	0.83

Picture 2

Picture 3

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

The equivalent resistance value of the circuit above was measured at 2530Ω. The calculated value is 2519.7Ω.

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

The equivalent resistances are the same with or without the 5V power supply. Resistance is independent from voltage or current.

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 two sides of the potentiometer are A and B. The middle terminal is C. AB will always be 10KΩ, however, AC and BC may change based on the position of the knob. Video 1 describers the potentiometer.

Video 1

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 voltage V1 can obtain would be 5V, the minimum would be nearly 0V, When the knob position is at the top of the resistor and V1 measures whole resistor, V1 would have 5V. As you move down the knob, V1's voltage will decrease. When the knob is at the bottom of the resistor and V1 measure the voltage across the wire, V1 will have nearly no voltage running through it.

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

V1 is not related to V2 for voltage. V1 always equals to 5V. V2 may change because of the knob adjusting the resistance of the resistor. Adjusting the resistor will change the current of the circuit but the voltage will stay the same. Video 2 discusses the values of V1 and V2.

Video 2.

11. For the circuit below, YOU SHOULD NOT turn down the potentiometer all the way down to reach 0 Ω. Why?

Picture 4

You should not set the potentiometer all the way down to 0Ω because then it will short the circuit. None of the current will go to the 1K fuse if the meter is at 0Ω. Picture 4 is above and shows the circuit we built to show how the fuse would be shorted.

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) 

The current of 1kΩ resistor will be 5.1mA when there is a 5.1V power supply. Unless the pot is turned down until there is no resistance and then the circuit is shorted, the current of 1kΩ should not change. Videos 3 and 4 describe this relationship.

Video 3

Video 4

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

Voltage division is how voltage is distributed across resistors in series. A voltage divider is a piece of equipment that allows you to decide how voltage is distributed within a series circuit. You can adjust the resistance of the potentiometer to decide the voltage drop off of resistors after it.

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

Current division is how current is distributed across resistors in parallel. A current divider is a piece of equipment that allows you to decide how current is distributed within a parallel circuit. You can adjust the resistance of the potentiometer to short parts of a circuit or make more current flow through a set resistor.