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.