EECS
2015+1-1,2,3+all.pdf

# Figure 7 this screenshot of lab data presents the i v

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Figure 7. This screenshot of lab data presents the I-V characteristic of a light-emitting diode (LED). The voltage is on the horizontal axis, which has linear scale from 0 to 2 V; the current is on the vertical axis, which has linear scale from 0 to 27.5 mA.The LED’s conductivity is practically zero until the voltage across the diode exceeds ~1.6 V, and rapidly grows above this limit. As already mentioned, a part of the I-V curve in Figure 7 can be approximated with a straight line, as sketched in Figure 8. Figure 8. This is a zoomed-in part of the same screenshot as in Figure 7. The straight line shows a possible linear approximation for the I-V curve in the range 1.86 – 1.96 V. Book Page 37

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EE for the 21 st century Review the basics 1-1-3 Ohm’s law – and beyond © 2015 Alexander Ganago Page 9 of 11 Last printed 2015-07-24 6:18 PM File: 2015 1-1-3 Ohm's.docx The slope of the I-V curve in Figures 7 and 8 is proportional to the electrical conductance of the diode. Even at the first sight it is clear that the conductance in the range 1.86 – 1. 96 V is greater than that at lower voltages. Mathematically, the differential conductance of the diode in the range 1.86 – 1.96 V can be found from the slope: ࠵? = 27 . 5 ࠵?࠵? 5 ࠵?࠵? 2 . 0 ࠵? 1 . 8 ࠵? = 22 . 5 ࠵?࠵? 0 . 2 ࠵? = 0 . 025 ࠵? 0 . 2 ࠵? = 0 . 1125 ࠵? Thus the differential resistance of the diode within this range of voltages equals: ࠵? = 1 ࠵? = 1 0 . 1125 Ω = 8 . 89 Ω T YPICAL PROBLEM FOR SELF - ASSESSMENT Which of the sketches above belongs to the circuit component whose electrical conductance grows as the applied voltage grows? A. Only sketch 51 B. Only sketch 52 C. Both sketches 51 and 54 D. Both sketches 52 and 53 E. Only sketch 54. Book Page 38