Scott Bertics
6/22/11
EE 47
Lab 1 Questions

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)
For the red LED:
V = I*R
5V = 0.03A * R
R = 167 Ω total resistance in the circuit.

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.
167 Ω represents the minimum resistance because lowering the resistance would result in an increase in current and therefore possible damage to the LED. Conversely, an increase in resistance would decrease the current and no damage would likely occur.

What is the resistance range of the potentiometer?
The multimeter read between 0.21 Ω and 9.87 kΩ, so the range is approximately 0Ω – 10,000Ω.

Does it matter what order the components of your circuit are arranged between power and ground? Why or why not?
No, the order of the components in this circuit is not important. Regardless of the order of the circuit, 5 volts of potential are lost between power and ground. In a series circuit, R_{total} = R_{1} + R_{2} + … so the order of the various resistances does not affect the total resistance.

Using this battery, what is the minimum resistance required for use with your LED?
Setup – 9V battery and a red LED rated at 30mA or 0.03A
Using Ohm’s Law:
V = I*R
9V = 0.03A * R
R = 300 Ω minimum total resistance for the entire circuit
Comments (1)
Benjamin Tee said
at 7:42 pm on Jul 10, 2011
Good job! You need to account for voltage drop across the LED as well in your calculations next time..
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