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# Richard Lin Lab 1

last edited by 6 years, 2 months ago

#### 2. Controlling the Brightness of LEDs

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.

Red light:

V=5V

Vf=1.85V

I=30mA=0.03A

V=IR

R=V/I=(V-Vf)/I=(5V-1.85V)/0.03A=3.15V/0.03A=105 Ohms

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.

It is the minimum resistance. If it's lower LED might fail.

c. What is the resistance range of the potentiometer?

About 0 Ohms to 10 KOhms

#### 3. Basic LED Circuit with Switch

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

It doesn't matter because the overall resistance and current doesn't change as you move the components, and no matter where you put the switch, as long as it is not pressed it will not be a complete circuit.

But it is important to make sure the longer end of the LED should always be facing the positive side

#### 4. Battery-Powered LED with Switch on Breadboard

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

Red light:

V=9V

Vf=1.85V

I=30mA=0.03A

V=IR

R=V/I=(V-Vf)/I=(9V-1.85V)/0.03A=7.15V/0.03A=238.3 Ohms