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Lab1-Orientation and LED

Page history last edited by Anisha Padwekar 7 years, 1 month ago
    1. 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.

      1. R=V/I

      2. Since the whole circuit is in series, any point in the circuit must have a current of 25mA (I am using a green LED)

      3. Typical voltage drop from LED =2.2V

      4. Vpower-VLED=5V-2.2V=2.8V

      5. R=2.8V/25mA=112 ohms

    2. 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.

      1. Minimum resistance (you can increase the resistance)

      2. The LED would fail if you lowered the resistance

    3. What is the resistance range of the potentiometer?

      1. 0 ohms-10 kiloohms

    4. No. No matter what the voltage drop across the circuit will be the same and the current in the circuit will always be the same no matter which order. Therefore, nothing is changed by rearranging the order of circuit elements (electric current will flow through everything regardless). All that has to remain the same is the orientation of certain elements (the LED must always have its longer leg pointing towards power).

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

      1. 9-2.2=6.8V

      2. 6.8V/25mA=272 ohms



Note: What I mentioned about the resistance was wrong (I recalculated after the video was taken). 


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