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Lab1-LED

Page history last edited by Vivien Tsao 7 years ago

2)

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.

 

Our 5V power supply powers a 25mA LED with a 2.2V forward voltage.

According to Ohms law:  

R=V/I 

Minimum Resistance =V/Max LED Current 

Voltage=Voltage of Supply-Forward Voltage of LED 

V=5-2.2=2.8V

Min Resistance = 2.8V/25mA

Min Resistance =112ohms

 

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 LED would fail if the resistance was any less than 112 ohms, because a lower resistance would cause more current to flow through the LED than it is rated for.

 

c. What is the resistance range of the potentiometer?

 

0-10k ohms.

 

3)

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

 

No, because the components are wired in series, and a series circuit maintains the same current throughout.

 

4)

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

 

Our 9V power supply powers a 25mA LED with a 2.2V forward voltage.

According to Ohms law:  

R=V/I 

Minimum Resistance =V/Max LED Current 

Voltage=Voltage of Supply-Forward Voltage of LED 

V=9-2.2=6.8V

Min Resistance = 6.8V/25mA

Min Resistance =272ohms

 

Video:

http://www.youtube.com/watch?v=qT79nXxKKQE&feature=youtu.be

 

 

Comments (1)

Vivien Tsao said

at 5:49 pm on Jul 11, 2013

Good job! :]

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