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Hajime Lab 1 Report

Page history last edited by Vivien Tsao 7 years ago


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.


V = Voltage

I = Current

R = Resistance


V = IR

I used 5V to power the circuit. V=5

I used a red LED so I need 30mA. I=30mA

The forward voltage of the LED is 1.85V


(5-1.85) = .03R

3.15 = .03R

3.15/.03 = R

R = 105


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 from a) is the minimum resistance. If the resistance is lower, the LED will most likely fail.


c. What is the resistance range of the potentiometer?

It was a 10K potentiometer.
However, the measured resistance was 0 to 9.8K using the oscilloscope.


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

Yes. It matters because if the circuit links the power into the LED before going through the resistor, all the voltage would go through the LED before it gets resisted by the resistor. However, after the mighty resistor, the LED and the switch is interchangeable.

-0.5 Is this true? Would the voltage drop change?


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


V = IR

I used 9V to power the circuit. V=9

I used a red LED so I need 30mA. I=30mA

The forward voltage of the LED is 1.85V


(9-1.85) = .03R

7.15 = .03R

7.15/.03 = R

R = 238.3


Comments (1)

Vivien Tsao said

at 6:51 pm on Jul 11, 2013

Good job! :]

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