Lab 1 - Circuits

Simple Circuit

 

1. What is the purpose of the resistor?
1. The purpose of a resistor is to drop the voltage to a desired level. In this lab, the source was 5V, however, the LED only took 2V. So we had to use a resistor to adjust the voltage for the LED
2. Using Ohm’s Law (V=IR), what is the current running through this circuit?
1. 5V = I * 560Ω
2. 5V/560Ω = I
3. 0.000892 A = I
4. 8.92 mA = I
3. Using Ohm’s Law again, calculate the resistor value you would have to use in order to have only 15mA of current in this circuit?
1. 5V = 15mA * R
2. 5V / 15mA = R
3. 5V / 0.000015A = R
4. 33333Ω = R
4. Assuming the LED drops 2.2V of voltage, how much voltage is dropped by the resistor?
1. Since there are 5V in the circuit and the LED takes 2.2V, the resistor is dropping 2.8V in a 5V circuit
   
   

Simple LED circuit with Switch

1. Looking at the schematic diagram, if you moved the switch so that it was connected between the resistor and the LED, how would the circuit’s behavior change?
1. not at all, because the switch is still needed to close the circuit, no matter where it is
2. Looking at the schematic diagram, if you moved the switch so that it was connected between the LED and ground, , how would the circuit’s behavior change?
1. not at all. see above

Simple LED circuit with Potentiometer 

1. Why is the 560Ω resistor necessary?
1. because of the LED. The current is dropped to ca 2V before going into the potentiometer so the LED does not break. This has to happen because the potentiometer may have 0Ω when turned down.
2. How much current is flowing through the circuit when the 10kΩ potentiometer is turned all the way up (offering the maximum resistance)?
1. together with the other resistor the maximum resistance in the circuit would be 10,560Ω. Now we can use Ohm’s law to find the current.
2. 5V = I * 10,560Ω
3. 5V/10,560Ω = I
4. 0.00047348A = I
5. 0.47mA = I
6. When the potentiometer is at 10kΩ the current is at 0.47mA

3. What other types of variable resistors do you know about (name at least 4)? 
   

   1. the knob on an eletric stove
   2. a dimming light swtich
   3. the photosensor in our phones controlling the screen's brightness
   4. a knob regulating a stereo's loudness 

Dueling LEDs

1. Give a quick (1-2 sentences) explanation of why this circuit behaves the way it does. Include an explanation for how the current going through each LED is affected by a single turn of the potentiometer
1. The current always seeks for the lowest path of resistance. By turning the knob on the potentiometer, the resistance for each path changes. The path with less resistance is more attractive for the current and, thus, the LED on the path is lit more than the other.

Capacitor Charging Unit

1. How does adding a 2.2kΩ resistor between the pushbutton and the capacitor affect the capacitor’s charging behavior?
1. A resistor does not change the voltage but the current. This can be seen from Ohm’s law as calculated earlier. The current is measured by how many electrons are passing a point in one second. Assuming that the capacitor has no resistance, this means that the capacitor is charged at a slower rate, however, at some point will reach full charge.

Capacitor Discharging

1. Looking at the circuit schematic diagram, why does the capacitor discharge up through the LED part of the circuit, and not directly from the capacitor down to ground?
1. Once the button is released, there is a “new” circuit where the capacitor is the power source. Thus, it cannot discharge directly down to ground and discharges through the LED.