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# Lab Report 1 - Grace Kwan

last edited by 7 years, 5 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.  Hint: Make sure that you account for the forward voltage drop (Vf) of the LED that you're using.

(5V - 2.2V) / .025 A =  112 ohms.

Note that Vf = 2.2 in our calculations, so we'll use a 150-ohm resistor to be conservative.

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.

Minimum resistance - if we lowered the resistance, the LED would likely fail.

c. What is the resistance range of the potentiometer?

Roughly 0 ohms - 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 components are all in series, so the same voltage will be applied over and the same current will flow through all of them. In addition, the switch would interrupt the circuit no matter the order.

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

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

(9V - 2.2V) / .025 = 272 ohms, so we'll use around a 300-ohm resistor.