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Page history last edited by Benjamin Wang 5 years, 2 months ago

2a. 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.


Assuming a yellow LED with a 5V power supply, and a forward voltage of 2.0V, the resistance necessary to limit the current to 25 mA is


V = IR

R = (5V-2V)/25mA

R = 120 ohms


2b. 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 is the minimum resistance. A lower resistance would result in greater current in the LED and would make it more likely to fail.


2c. What is the resistance range of the potentiometer?


The potentiometer has a measured resistance of 9.7kohm.


3a. Does it matter what order the components of your circuit are arranged between power and ground? Why or why not?


The components do not have to be in any order since they are in series. All of the current is in a loop and the voltage drops across each component are the same because of this.


4a. Using this battery, what is the minimum resistance required for use with your LED?


Using a 9V battery, the minimum resistances assuming a yellow LED operating at 25 mA is


V = IR

R = (9V-2V)/25mA

R = 280 ohms

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