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# Matthew Kim labwriteup1

last edited by 8 years, 10 months ago

Matthew Kim

June 26 2011

Laboratory Experiment #3

• # Set the power as 5V

Case 2: Controlling the brightness of LEDs

(This picture is from Aditya Manikantan)

• # Connect potentiometer with the resistor and the longer lead of LED.

Case 3. Basic LED circuit with switch on breadboard

• Follow the procedures in Case 1 to set up the basic circuits.

• Connect the switch with the shorter side of LED and use a jumper wire to complete the circuits.

Case 4. Battery-powered LED with switch on breadboard

• Disconnect the ‘banana’ connectors from the breadboard.

• Put a 9V battery and hook up with the breadboard using battery clips

• Change the resistor based on your calculations regarding the amount of voltage. In this case, I will use a resistor of 300ohms.

Results (data):

It works perfectly when the circuits are completed. I have come to a realization of how each component used in this lab functions as well as how they have to be used to work efficiently.

Questions:

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)

- I am using a red LED which has the current limit of 30mA. According to the ohms law- V=IR -, R has to be 166ohms considering I is 30 mA (0.03 A) and V is 5 voltage.

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.

- If the resistance is higher than 166ohms, then the current has to be less than 30 mA because they are inversely proportional. Therefore, 166omhs of resistance is the minimum resistance when 30 mA of LED is used. If the resistor had less than 166ohms, it would damage the LED.

c. What is the resistance range of the potentiometer?

- It is from 0 to 10 kohms according to my measurement using the multimeter.

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

- I do not believe it matters as well as the circuits are completed. Any electronics function normal when the circuits are completed and the current is flowing from the power(+) to the ground(-). The order will matter if the circuits are parallel but in a series circuit, the order should not matter .

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

- The batter has 9 volts and the limit of the current is 30mA ( 0.03A ). Thus, the resistance should be higher than 300 ohms according to the ohms law. 300 ohms of resistance is the minimum resistance for the red LED that I used.

Conclusion:

To begin with, my hypothesis was right. The circuits functioned as long as the circuits were closed regardless of the components I’ve utilized. I tested the circuits with a potentiometer to control the brightness, a switch to turn on and off the power, and a battery to make the circuits portable. Things went smoothly without major problems and following the safety precaution I set myself before the experiment played an important role to be more delicate with the circuits. It was profoundly satisfying to apply the prior knowledge to build something tangible and witness that it actually worked. What I have learned through this lab will perpetually used in the field that I will major in and it was a step towards my future.