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ENGR 1110: Introduction to Engineering
Lab 3
Items needed:
- Digital Multimeter (DMM)
- Power Supply
- 1 Breadboard
- 1 wire kit
- 4 1k Ohm resistors
- 1 xF capacitor
- 1 LED
Pre-Lab Preparation Work the circuit analysis problems indicated below in italics before coming to lab. This will help you to know what to expect when you do the actual measurements.
In-Lab Activity In this lab you will examine the relationships between basic circuit elements, voltage, current, and resistance.
- Single resistor a. Turn on the power supply, making sure the leads are not shorted (connected). Set the output voltage of the power supply to 9 volts. Set your DMM to read voltage and connect the positive lead (red) of the power supply to the positive lead (red) of the DMM. Connect the negative lead or common (black) of the power supply to the common lead (black) of the DMM. Read the measured voltage on the DMM. Does it read exactly 9 volts? Why or why not? Switch the leads so that the positive lead of the power supply is connected to the common of the DMM, and vice versa. What does the DMM say the voltage across it is now?
b. Look at the circuit in Dia. 1. Using Ohm’s law, calculate the current flowing in the resistor given a supply voltage of 9V and a resistance of 1kOhm.
c. Wire up the circuit shown in Dia. 1 on your breadboard, referring to Fig. 1 if you need help with breadboard wiring. Ensure the output voltage of the power supply is 9V, and measure the voltage drop across the resistor with the DMM. Remember the DMM leads are placed on either side of a component to measure a voltage drop across it. How does the measured voltage compare to the supply voltage?
Diagram 1
Figure 1: Breadboard layout of Diagram 1
d. Set up the DMM to measure current, and insert its leads into the circuit to measure the current flowing through the resistor, as shown below. Remember, the DMM leads must be in the path of current flow (inline with the circuit) in order to measure current. How does the measured current compare with the current calculated using Ohm’s law?
- Resistors in series a. Look at the circuit in Dia. 2. Using Ohm’s law and the formula for a voltage divider, calculate the voltage drop across each resistor as well as the drop across both resistors, given a supply voltage of 9V and resistor values of 1kOhm each. Remember, the sum of the voltage drops in a series circuit is equal to the supply voltage. Calculate the current flowing through the circuit (remember, the same current flows through both resistors).
b. Wire up the circuit shown in Dia. 2 on your breadboard, referring to Fig. 2 if you need help with breadboard wiring. Ensure the output voltage of the power supply is 9V, and measure the voltage drop across each resistor and across both resistors with the DMM. How do the measured voltages compare to the supply voltage? Do the measurements agree with your calculations? If not, explain why.
Diagram 2
Figure 2: Breadboard layout of Diagram 2
voltages compare to the supply voltage? Does the measurement agree with your calculations? If not, explain why.
Diagram 4
Figure 4: Breadboard layout of Diagram 4
c. Set up the DMM to measure current, and insert its leads into the circuit to measure the current flowing through each leg of the circuit, as shown below. How do the measured currents compare with the currents calculated using Ohm’s law and current division? Do the measurements agree with your calculations? If not, explain why.
- Diode circuit a. Look at the circuit in Dia. 5. Remember, diodes (such as LEDs) only conduct current in one direction (when the triangle of their symbol faces in the direction of current flow). Diodes have given voltage drop across them, usually around 0.6V. Given this, a power supply voltage of 9V and a resistor value of 1kOhms, calculate the voltage drop across the resistor and the current flowing in the circuit.
b. Wire up the circuit shown in Dia. 5 on your breadboard, referring to Fig. 5 if you need help with breadboard wiring. The longer leg on an LED is the positive lead, corresponding to the line on the end of the triangle in the LED circuit drawing. Ensure the output voltage of the power supply is 9V, and measure the voltage drop across the resistor and the current flowing in the circuit with the DMM. How do the measured voltages compare to the supply voltage? Does the measurement agree with your calculations? If not, explain why. Turn the LED around in the circuit so its positive and negative leads are swapped. What happens to the LED light? What about the voltage drop? What about the current flow?
Diagram 5
Figure 5: Breadboard layout of Diagram 5
- Diode in parallel circuit a. Wire up the circuit shown in Dia. 6 on your breadboard, referring to Fig. 6 if you need help with breadboard wiring. Notice that the circuit forms a current divider network, so the current flowing through each leg of the circuit is less than the total amount flowing in the circuit. Notice that the LED is dimmer in this circuit. This is because the LED has less current flowing through it. Measure the voltage drop across the LED, noticing that it is the same as in the previous setup.
Diagram 6
Figure 6: Breadboard layout of Diagram 6
