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Kingston's Lab Report 1

Page history last edited by Kingston Tam 7 years, 2 months ago Saved with comment

Lab Report 1


2. Controlling the Brightness of LEDs 


a. What resistance do you need to limit current to 30 mA (if using red LED) or 25 mA (if using yellow or green)? Be sure to state which color LED you are using. This resistance refers to the total resistance in series with the LED.


From Data Sheets for Green LED: We will need to limit the current to 25 mA and the typical Vf of the LED is 2.2V.


Calculation: Therefore, effective voltage is 5V - 2.2V = 2.8V and the required resistance: R = V / I = 2.8 / 0.025 = 112 ohms


b. Is the resistance from question a) a maximum or minimum resistance? That is, in which direction if you change the resistance (higher or lower) would the LED likely fail.


The resistance in a) is a minimum resistance because the lower the resistance the higher the current and thus if you lower resistance it will likely fail because a higher current will flow through the circuit.


c. What is the resistance range of the potentiometer?


The resistance as measured by the multimeter ranged from 0.35 ohms to 9.55 kohm.


3. Basic LED Circuit with Switch 


a. Does it matter what order the components of your circuit are arranged between power and ground? Why or why not?


It does not matter because all the components of the circuit are in series and the resistances add in series so the same voltage drops/current will occur in each of the components and the switch when opened will break the entire circuit regardless of position because there is only one path from power to ground.


4. Battery-Powered LED with Switch on Breadboard 


a. Using this battery, what is the minimum resistance required for use with your LED?


For a 9V battery, the effective voltage across the resistor (calculated the same way as 2a) would be 9 - 2.2 = 6.8V.  We then calculate the minimum resistance required as 6.8 / 0.025 = 272 ohms.






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