Week Three

Week 3

Not Shocking People

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: Equivalent Resistance Comparison Table

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

When measuring the current in series with the DMM, we measured 39.4 mA. When measuring current in parallel, we read a measurement of 0 Amps, but the machine was also registering an overload. This is because when we connect the DMM in parallel, we are essentially shorting the current that would have flown through the resistor, as it is now running through the DMM which is acting as 0 Ω 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 current on both resistors are the same at around 29 mA. The voltage on the 47 Ω resistor is 1.38V. The voltage on the 120 Ω resistor is 3.58V. 

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 voltage on the 47 Ω resistor is 4.94V. The current on the 47 Ω resistor is 92.8mA. The voltage on the 120 Ω resistor is 4.94V. The current on the 120 Ω resistor is 39.4mA.

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

Figure 2: Circuit Configuration for Problem 5

a. Current on 2 kΩ resistor,

Figure 3: Measuring the 2kΩ resistor, finding 2.03 mA

b. Voltage across both 1.2 kΩ resistors.

Figure 4: Measuring a 1.2kΩ resistor, finding .853 V

Figure 5: Measuring a 1.2kΩ resistor, finding .722 V

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

2519.7Ω

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

The resistance is 554 Ω without the power supply. The DMM was not able to read the resistance while the power source was connected. This is because the DMM acts as a voltage source itself. When you apply an additional source to the circuit, you confuse the DMM. 

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)

Firgure 6: Explaining the operations of a potentiometer 

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 that could be obtained was 0V as the potentiometer was turned fully towards the ground terminal, which meant all of the resistance was concentrated between voltage input and V1 terminal, causing the V1 to be 0.  The maximum voltage that could be obtained was 5 V as the potentiometer was turned fully towards the voltage input terminal, causing all of the resistance to be between the ground and the V1 terminal, allowing V1 to be 5V.

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)

Figure 7: Explaining the relationships between measuring V1 and V2

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

This is because when turning the potentiometer all the way down, this will cause the circuit to short through the potentiometer, frying it.

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).

Figure 8: Explaining how the currents are related, as well as the effect of the knob position

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

A voltage divider divider is a device with two resistors in series with an input. It can convert a large voltage into a small one, making the output smaller than the input. For this experiment the potentiometer works as a voltage divider. By turning the knob we can adjust the output voltage. When the knob is turned completely towards the input, the voltage drop is near zero, as the current is able to bypass the resistor, or short. When the knob is turned completely towards the ground, the voltage drops to zero, due to the entire interior resistor being utilized. 

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

A current divider is a device that uses to parallel resistors to divide current from a power source. This allows for different amounts of current to be applied to different parts of the circuit. For our experiment we connected a current divider(potentiometer) in parallel with a 1k resistor. This allowed for different amount of current to pass through the potentiometer as we increased and decreased the resistance.