Voltage and Current Divider

DC Experiment 3

Background

Voltage Divider:
In a series circuit as shown in Figure 3.1, the current through all components is same, therefore I 1 to I4 are identical current in the circuit. According to voltage divider rule, the voltage across each resistor can be easily calculated by the given equations:
Current Divider:
In a parallel circuit shown in Figure 3.2, the voltage across each resistor is same, but the current flowing through each branch may vary depending on the resister value. The current divider rule allows each branch current to be calculated by the given equations:
In this section we will measure the voltages and currents in series and parallel circuits to verify the voltage and current divider rules. Note that we do not provide all breadboard layout figures so you can take a moment to plan the breadboard layout before setting up the actual circuit.

Procedure

Part I: Voltage Divider Circuit
  1. 1.
    Construct the circuit of Figure 3.3 on the breadboard. Set Vs = 6V and choose R1 = 1.0 kΩ, R2 = 3.3 kΩ, and R3 = 4.7 kΩ.
  1. 2.
    Using the voltage divider formula, calculate the voltage drop on each resistor and record in Table 3.1 column 2. Use the nominal resistor values for calculations.
  2. 3.
    Ensure Vs is very close to 6V (measure by VEGO) and also measure the voltage drop of each resistor. Record the measurements in Table 3.1 column 3.
Part II: Current Measurement
  1. 1.
    Set up the circuit in Figure 3.4. Think about the breadboard layout for current measurement. Set power supply to 6V and choose R1 = 1.0 kΩ and R2 = 4.7 kΩ for resistor values.
  1. 2.
    The breadboard layout example is shown in Figure 3.5. Note that the yellow and green conducting wires can be replaced by an ammeter while measuring currents.
Note that the long red and black wires connect the power rails on each side of the breadboard.
  1. 3.
    sing the current divider formula, calculate the expected currents through R1 and R2. Record the results in Table 3.2 column 2.
  2. 4.
    Set VEGO to small current mode [mA] and measure the actual current through each resistor. Record the measured currents in Table 3.2 column 3.

Exercises

  1. 1.
    In Table 3.1 and Table 3.2, compare your calculated and measured results. Are they close enough to validate your experiment being correctly implemented?
  2. 2.
    Design a circuit so that the voltage across R3 is around 4V. Choose the resistor from your given components and show your procedures to obtain the value of R3. You can also verify the result on breadboard.
  1. 3.
    Build the circuit below. Take measurements to complete Table 3.3, and then answer the following questions:
a. Measure voltage at ‘a’. To do this, the black probe is connected to ‘c’, the red probe is connected to ‘a’. Record Va in Table 3.3 column 2.
b. Similarly, measure Vb and record the measurement in Table 3.3 column 2. Note that R3 is an open circuit since the terminal at ‘b’ is unconnected.
c. Now completely remove R3 from your breadboard, then measure Va and record the value in Table 3.3 column 3.
Based on the measurements above, what is the voltage drop between Va and Vb? Is there a current flowing through R3? Is the voltage divider law still valid for the circuit above?