01-Mar-2016: Day 3

Exercise 1:

Problem:
Attaching live wires to opposite ends of a hot dog... what will happen?

As a group we predicted that the hot dog would quickly crisp and then burn.

Instead the hot dog slowly began to cook... very slowly.

Now, what will happen if LEDs are inserted to the hot dog, some parallel and some perpendicular to the axis. It was predicted that only the ones connected parallel would light up.

Furthermore, it was also predicted that if the LED leads were spread open, then they would illuminate more intensely due to a greater voltage drop.

Exercise 2:

Practice solving currents and voltages.

Problem:
Finding the current through the 4 ohm resistor drawn below. Applying KCL to the node labeled "a" we could obtain an equation as the sum of the two outer currents. Ohm's law then can be used to solve the voltage across the same 4 ohm resistor.

Problem:
Again, there are known and unknown elements in the circuit that must be solved for.

While the top circuit diagram is solvable, it can also be redrawn with a single node in order to simplify.The current entering a node must be the same current going out, therefore, the sum of the current through the branches exiting the node must add up to the current entering.

Exercise 3:

Problem:
Given the circuit below with known voltage source and resistor values, we are to calculate the voltage across each resistor.

Exercise 4:

Problem:
Quick look into having an LED placed into the circuit. We were to calculate resistance and the power required to run the LED.

The LED has a voltage and current range which we used to calculate a range of power.

Exercise 5:

Problem:
Quick review of finding equivalent resistance, in this case for a parallel circuit.

Exercise 6:

Lab:
"Dusk-to-Dawn Light"
In this lab we will be using a photocell which is a light sensitive resistor, along with a transistor that will act as our switch, all connected to a constant voltage source. The photocell's resistivity only decreases as its exposure to light increases, and increases as the ambient light is decreased. A transistor has three leads, typically in line, where the one of the outer leads is an input and the other an output. The center lead can be described as a door, and can only be opened by applying a strong enough current.

 As depicted above, there is a point on the left side of the circuit where the current may either enter the photocell of the the center lead of the transistor. As the photocell's resistivity increases, the transistor's door eventually opens, allowing the flow of current through the transistor.

 Below are the calculated and measured values for the voltage across the photocell.