Goal: to measure β value for the transistor 2N3904
Experiment:
1) Build a circuit according to the following scheme on a breadboard. Instead of using push button to turn on, we just closed the circuit to turn on the LED. LED turned bright. R1 = 220 ohms, R2 = 10,000 ohms, R3 = 680 ohms, Q1 = 2N3904 Transistor, D1 = LED.
2) R2 was removed, and we performed finger tip switching. Although not as bright, the circuit could be closed just by using our fingertip. Video is available in the following link: http://www.youtube.com/watch?v=Ok8e_V7VmqQ
3) According the following scheme, a circuit was built. R1 = R3 = 220 ohms, R2 = R4 = 1000 ohms, P1 = 10k potentiometer, Q1 = 2N3904 Transistor. A 6V power supply was used in this experiment. After collecting 10 data points for Ib and Ie, the data was plotted, and the slope (β value) was determined to be 7.8060.
Conclusion: The maximum amount of Ib that could be achieved in the lab was 0.308 mA (instead of the expected 4 mA) while the minimum was 0.119 mA. Therefore, 10 points were picked between 0.308 and 0.119 mA. The β value of 7.8060 was far off from the expected 50. This might be because the transistor has not reached its active phase therefore the slope is not that steep. In future experiment, the values of all circuit elements must be carefully calculated to reach higher values of Ib.
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