# 1 reconnect the three resistors in parallel now

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1. Reconnect the three resistors in parallel. Now, follow the diagram as shown in figure 3, and connect the three resistors to the power supply. Arrows show direction of current flow. Set the power supply to 5V and measure the voltage drop across each resistor, the total voltage drop across the positive and negative sides of the circuit, the current in the circuit and the current through each resistor. Write down your results. You will need to change the voltmeter and ammeter connections accordingly to make all these measurements. When measuring the voltage across a resistor while also measuring current, connect the voltmeter only across the resistor, not across the resistor and ammeter. 2. Calculate the current for each resistor and enter it in your data table. Calculate the total current of the three resistors by adding your measured values (IP = I1 + I2 + I3 + ...). Calculate the predicted current (I*) by substituting your measured values for the voltages and resistances of each resistor into the formula I*=V/R. Table 1: Measurements of Resistors R1 R2 R3 R4 R12s R23p R123 R1234 d R1234 e R1234f Measured R using DMM Formula of eq. resistance Calculated eq. resistance Table 2: Vs,V1, &V2 as shown in figure 2 in the lab manual: Vs V1 V2 4.9 3.3 1.5 Table 3: Vs,V1, &V2 as shown in figure 5 in the lab manual: Vs V1 V2 4.9 4.8 4.8 Table 4: Is,I1, &I2 as shown in figure 6 in the lab manual: Is I1 I2 127 40.7 88 Table 5: Current and Voltage measurements of figure 3: Measured Data Calculated Data Source Voltage Vs 5 V 10 V V1 (v) V2 (v) V3 (v) V4 (v) I (mA) I1 (mA) I2 (mA) Not measured I3 (mA) Not measured
I4 (mA) Figure 3 Table 3: Brightness and Current observation in series circuits Source Voltage Cases Measured Current (mA) Observed Brightness Bright Less Brigh t Di m Very Dim No Ligh t Vs= 5V Fig. 3(a) Fig. 3(b) Fig. 3(c) Fig. 3(d) Fig. 3(d) but with one light bulb removed Table 4: Brightness and Current observation in Parallel circuits Source Voltage Cases Measured Current (mA) Observed Brightness Bright Less Brigh t Di m Very Dim No Ligh t Vs= 5V Fig. 3(a)
Fig. 3(b) Fig. 3(c) Fig. 3(d) Fig. 3(d) but with one light bulb removed Table 5: Brightness and Current observation of figure 4 circuit: Source Voltage Cases Measured Current (mA) Observed Brightness Bright Less Bright Dim Very Dim No Light Vs= 5V All 4 light bulbs are in circuit Vs=10V All 4 light bulbs are in circuit Light bulb #1 is removed Light bulb #2 is removed Light bulb #3 is removed Light bulb #4 is removed Figure 5 Although currents I2 and I3 are not measured directly you can find the values of I2 and I3 from the measured current in Table 5 (assume all the four light bulbs have the same resistance). Find the values of I2 and I3 (with all the four bulbs in the circuit) at
(a) S V = 5V: I2 = (mA), I3 = (mA) (b) S V = 10 V: I2 = (mA), I3 = (mA) Conclusion: The measured results were very close to the theoretical results which proves that the theory is actually correct.
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