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OBJECTIVES After performing this experiment, students should be able to: Construct a Wheatstone bridge circuit using 3 fixed resistors and a potentiometer Demonstrate the balanced and unbalanced conditions of a Wheatstone bridge Conduct an experiment to determine the relationship between the output voltage and varying resistance on one arm in a Wheatstone bridge circuit Conduct an experiment to determine the appropriate value of resistance to balance a bridge EQUIPMENT AND MATERIAL LIST 1

Electrical Engineering

OBJECTIVES

After performing this experiment, students should be able to:

• Construct a Wheatstone bridge circuit using 3 fixed resistors and a potentiometer
• Demonstrate the balanced and unbalanced conditions of a Wheatstone bridge
• Conduct an experiment to determine the relationship between the output voltage and varying resistance on one arm in a Wheatstone bridge circuit
• Conduct an experiment to determine the appropriate value of resistance to balance a bridge

EQUIPMENT AND MATERIAL LIST

1. Power supply

2. Multi meter

3. Resistors

4. Potentiometer

5. Jumper wires

* All the above are simulation-based components

PROCEDURE

Unbalanced condition

1. Select three fixed resistors R1, R2, R3 and one potentiometer Rx. Note down these R1, R2, R3 values in Table 1 as the measured values (The value of the three fixed resistors R1, R2, R3 remain the same throughout the experiment.)

2. Set the power supply to 5V.

3. Connect the circuit as shown in Figure 1.

4. Set the potentiometer Rx to a small value eg. 1kW

5. Calculate the expected value of Vap. Note this value down in Table 1.

6. Measure the value of the output voltage across a-b, Vab

7. Vary the potentiometer value by xW such that the new value of Rx is now 1k + xW

8. Calculate the expected value of Vap. Note this value down in Table 1.

9. Measure the value of the output voltage across a-b, Vab. Note this value down in Table 1.

10. Repeat steps 7-9 while varying the potentiometer values with fixed increments of xf).

11. Discuss your findings and show all relevant simulations and calculations in your report.

Balanced condition

1. Select three fixed resistors, R1, R2, R3 and one potentiometer Rx. Note down these values down in Table 2.

2. Set the power supply to 5V.

3. Connect the circuit as shown in Figure 1

4. Calculate the expected value of Rx when the bridge is in a balance state, Vab= 0.

5. From the circuit, tune the potentiometer, Rx, until Vab is zero. Note down this value of Rx in your table.

6. Repeat steps 1-5 using a different set of values for R1, R2 and R3.

7. Discuss your findings and show all relevant simulations and calculations in your report

R1       R2

Vin 5V  Vab  a Multimeter  b

Rx          R3

Figure 1: Wheatstone bridge circuit

NOTE

Analyze your results and discuss its relevance to the known theory and balance equation.

Does it support the theory? Any changes in polarity for the voltage readings? Does it increase or decrease in magnitude? Can it be proven why using the relevant equation? Can the values calculated for the potentiometer balance the bridge?

Results

Table 1: Unbalanced bridge

 R1 (in W) R2 (in W) R3 (in W) Rx (Measured)          (in W) Vab  (Calculated) Vab (Measured) 1 2 3 4 5 6 7 8 9 10

Validated by:

Table 2: Balanced bridge

 R1 (in W) R2 (in W) R3 (in W) Vab (Measured) Rx  (Calculated)        (in W) Rx (Measured)        (in W) 1 0 2 0 3 0 4 0 5 0

Validated by: