Lab 3 - Ohm's Law

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School

Algonquin College *

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Course

9104

Subject

Electrical Engineering

Date

Apr 3, 2024

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docx

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Uploaded by GrandRockGazelle46

ELN9104 Lab 3 – Ohm’s Law Purpose: The purpose of this lab is to apply Ohm’s Law and to learn how to measure current using a digital multimeter (DMM). Materials and Equipment:  5 resistors, chosen to meet specifications  1 47Ω resistor  1 red LED  1 1869 incandescent bulb – rated to 10V  Breadboard  Banana cables  Alligator clips  2 digital multimeters  DC power supply Procedure: LED Circuit 1. Complete the following calculations to determine the resistor values needed for the LED circuit. a. The LED requires 1.7V across to turn on. Using KVL, calculate the voltage across the resistor using the circuit in schematic 1. 2. Using your value for V R , and the current values in Table 1, calculate the resistors needed to achieve the desired current values. Table 1 Target current (mA) Calculated resistance (Ω) Resistance value used -rated (Ω) Resistance value used - measured(Ω ) Measured current (mA) V R (V) V LED (V) Brightness of LED 0.3 11000 10000 9810 0.3 3.26 1.74 Dim 1.0 3300 3300 3270 1.03 2.88 1.94 Bright 4.5 733.3 780 667 4.2 2.85 1.90 Bright 9 366.7 330 327 8.8 2.92 1.96 Bright 18 183.3 160 159 13 2.90 2.02 Bright V R If V s = 5V and the V LED = 1.7V, calculate V R V R= 3.3V Schematic 1 V LED

ELN9104 Lab 3 3. Look at the resistors in your kit and choose a resistor that is close to the calculated resistance. Measure this resistor and record these values in Table 1. 4. Build the circuit shown in Schematic 1 with the first resistor listed in Table 1. Note: the LED is a polarized component, which means that it has a positive side and a negative side, and will only light up if it’s connected as shown in Schematic 1. See Image 1 for details on how to identify the positive and the negative side of an LED. 1 5. Starting with a source voltage of 0V, slowly increase the voltage until the LED turns on. Measure the voltage across the LED and the resistor and record the values here: V S V R V LED 6. Set up one of the digital multimeters to measure current by placing it in series with the DC power supply. See Image 2 for details. 7. Apply the required voltage to the circuit and measure total current and the voltage across each component, record the values in Table 1. 8. Repeat step 7 for each resistor value. 9. Plot current vs resistance using MS Excel or by hand in the space below. Your plot should be well labeled and scaled appropriately for the space provided. 1 [1]How to identify terminal leads. Accessed: May 22, 2023. [Online]. Available: https://www.make- it.ca/3mm-led-specifications/ Imag e 1 [1] Image 2: how to connect the ammeter to measure total current Connect the following:  The positive of the power supply to the positive of the ammeter  The negative of the ammeter to the positive of the circuit  The negative of the circuit to the negative of the power supply

ELN9104 Lab 3 Incandescent Bulb Circuit 10. Measure the resistance of the 47Ω resistor and the bulb. Record the measured values in Table 2. Table 2 component Listed value (Ω) Measured value (Ω) Resistor 47 Ω 46.8 Bulb (cold bulb) 105 114 11. Connect the circuit as shown in Schematic 2. Current vs Resistance Current (mA) Resistance (Ω) Sch ematic 2

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