Transistor Switching Lab

The purpose of this lab was to introduce us to transistors and transistor circuits. As usual we began the lab by measuring the resistance of wires and to take out the breadboard. We were instructed to set up the circuit consisting of elements S1 (the pushbutton), R1 (180 ohms), R2 (10k ohms), R3 (680 ohms), Q1:2N3904, and a D1:LED according to a schematic diagram that was presented to us on our lab sheet. After doing so, we were instructed to press the push button and and to make an observation regarding the LED light.

As you can see, the light indeed turned on. We then used the voltmeter to check the voltages of the different elements in the circuit. 

The second part of the lab involved the fingertip switching. We were instructed to remove the push button and the R2 transistor and install two pieces of wire into the breadboard according to the diagram.  Then my lab partner placed both of the wires on his fingertip and noticed that the LED light glowed. 

After being instructed to lick his finger, my partner repeated this step again and noticed that the LED glowed even brighter. Next, we were instructed to measure the current flowing through a point A2 connected to the emitter given values of A1 connected to the base and to jot down these measurements in a table. The given currents through A1 were 0, 0.15, 0.30, 0.45, 0.60, and 0.75 mA, and we recorded values of 0, 38.02, 47.20, 52.30, 54.50, 55.10 mA, respectively for A2. This indicated a proportional relationship. Our instructor gave us a formula for computing the beta value, which was a simple ratio of A2 to A1, which was found to be 253.47 mA. The transistor was found to be saturated at 52.3mA. 

In conclusion, this was a very interesting lab assignment and and hopefully it will allow me and the other students to digest the textbook material regarding transistors much more easily.