Period ______Date ______
Lab Partners ______
______
______
AP Physics - DC Complex Circuits Lab
Purpose: To verify the behaviors of resistors wired in a complex DC circuit that includes both series
and parallel portions by comparing measured voltages and currents for chosen resistors
to calculations of voltage and current through each resistor.
Materials:
· Power supply (or batteries) that can be set to voltages between 3.0 volts and 6 volts
· Six different value resistors ranging from 50 ohms to 25000 ohms
· Four to five wire leads
· Multimeter
Procedure:
Part I – USING THE MULTIMETER as an OHMMETER
· Read and record the color band values of the six different resistors you chose in the data table, including the tolerance (%error) factor for each reading.
· Set the multimeter to read ohms and measure the resistor value for each of the six resistors you chose as shown in the diagram below. The resistor must be OUT of the circuit for this.
· Record the values you measured for the resistors in the data table.
· Calculate the % error of the code bands compared to the actual resistor measurements and record this in your data table. %error = |Rmeas- Rcode|(100)
|Rmeas|
Part II – USING THE MULTIMETER as a VOLTMETER
· Set up a simple series circuit with the power supply connected to ONE of your resistors
· Record the measured (not band code) value of the resistor you are using
· Resistor measurement: ______
· Set the voltage on the power box to somewhere between 3 and 6 volts (or use a single dry cell) and turn the power supply on.
· Set the multimeter to read DC Volts at the 20 Volt setting, then turn on the multimeter
· Measure and record the voltage across the resistor as demonstrated in the picture below by:
o touching the positive (red) probe to the side of the resistor leading to the positive (red) connection at the power source and simultaneously
o touching the negative (black) probe to the side of the resistor leading to the negative (black) connection at the power source (see diagram on following page)
· If you get a negative reading, switch the probes around (positive to positive, negative to negative)
Voltage measurement: ______
Part III – USING THE MULTIMETER as an AMMETER:
· Disconnect the negative end of the power source line from the resistor and attach the power source directly to the negative probe on the multimeter.
· With the multimeter OFF, attach the positive probe of the multimeter to the free end of the resistor.
· Turn the multimeter dial to measure the biggest amount of DC current (200 DC mA)
· Turn on the multimeter and record the current measurement, being careful to note the prefix (milli-, micro-) before the amperage reading.
· If you get a reading of a numerical “1”, go to a lower scale setting or if you get no reading pm any scale setting, you probably need to turn on the power or change the meter fuse.
· Measure and record the current, then convert it to amperes from mA
Current measurement:______mA
Verify that Ohm’s Law worked by using your measured voltage and currents to see if you get the resistance value you used for this trial. Show your work below:
Part IV – COMPLEX CIRCUIT Setup
· Set up a complex circuit as shown below with the six different resistors you selected and measured in Part I.
· Label the circuit diagram below with the resistors you used, showing the correct location in the circuit for each resistor.
· Set the power box voltage to between 3 and 6 volts and label the diagram below with the value
· Measure and record:
o the total resistance from end to end of the circuit detached from the power source.
o the voltage drop across each resistor as demonstrated in class
o the currents through each resistor as demonstrated in class
o the total voltage across the power box.
o the total current from the power box to the first resistor (the one in series)
· Calculate and record:
o the total resistance for the circuit using the code value resistances.
o the total current expected for the entire circuit
o the expected voltage drops across each individual resistor.
o the expected current through each resistor
· Calculate the percent difference between your measured and calculated values for current and voltage, using the measured values as the true values.
Label your resistor values and the power source voltage setting value directly on the circuit diagram shown below.
R1 ______W
PD_____V
R2 ______W R3 ______W
R4 ______W R5 ______W
R6 ______W
DATA TABLE:
Power Box Voltage Setting : ______
BAND COLORS:
Resistor 1 colors______+/-tolerance______R1 Value ______+/-______%
Resistor 2 colors______+/-tolerance______R2 Value ______+/-______%
Resistor 3 colors______+/-tolerance______R3 Value ______+/-______%
Resistor 4 colors______+/-tolerance______R4 Value ______+/-______%
Resistor 5 colors______+/-tolerance______R5 Value ______+/-______%
Resistor 6 colors______+/-tolerance______R6 Value ______+/-______%
COMPLEX CIRCUIT
Quantity / Calculated value / Measured value / % ErrorR1 (W) / code value:
R2 (W) / code value:
R3 (W) / code value:
R4 (W) / code value:
R5 (W) / code value:
R6 (W) / code value:
Total Current (A)
Total Voltage (V)
Voltage R1
Voltage R2
Voltage R3
Voltage R4
Voltage R5
Voltage R6
Current I1
Current I2
Current I3
Current I4
Current I5
Current I6
SAMPLE CALCULATIONS
Quantity / Formula / Substitution / Answer with Units% Error
Rmeasured versus
Rcalculated
Rtotal (W)
Itotal using meas V and R (A)
Vdrop
R1 =_____ W
Vdrop
R2 =_____ W /
Vdrop
R3 =_____ W
Vdrop
R4 =_____ W
Vdrop
R5 =_____ W
Vdrop
R6 =_____ W
% Error Total V
Vmeasured versus
Vcalculated
I through resistor
R1 =_____ W
I through resistor
R2 =_____ W /
I through resistor
R3 =_____ W
I through resistor
R4 =_____ W
I through resistor
R5 =_____ W
I through resistor
R6 =_____ W
% Error ITOTAL
I TOTAL (meas) versus
I TOTAL (calc)
QUESTIONS:
1. What would happen if the total voltage in the circuit was not used up by the resistors?
2. a. What happens if you use the multimeter as a voltmeter when you have it set as an
ammeter? WHY? (Look this up)
Reference:______
b. What happens if you use the multimeter as an ammeter when you have it set as an
voltmeter? WHY? (Look this up)
Reference:______
3. Should the voltmeter have a high or a low resistance? WHY?
4. Should the ammeter have a high or a low resistance? WHY?
5. What three possible reasons might cause you to get a zero reading on the ammeter?
6. How did the sum of the voltages in R4 and R5 compare to the voltage in R6? WHY?
7. What happens to the voltage reading for R5 if the value of R4 is huge by comparison?
8. How did the voltage to R3 compare to the voltage in R2? WHY?
9. How did the current through R3 compare to the current through R2? WHY?