Question 53 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is B. ### Explanation for Option B (The diode is functioning properly) A silicon diode is a semiconductor device that acts as a one-way switch, demonstrating low resistance to current flow in one direction (forward bias) and extremely high resistance in the opposite direction (reverse bias). 1. **Figure A (Forward Bias):** The reading of 4.7 ohms is very low resistance, indicating that the diode is conducting current easily, which is the correct behavior for forward bias. 2. **Figure B (Reverse Bias):** The reading of 490 ohms is much higher resistance (over 100 times higher) than the forward reading, indicating that the diode is effectively blocking current flow. Although 490 ohms is not an "ideal" infinite or megaohm reverse resistance reading, the presence of a wide resistance differential (4.7 $\Omega$ vs. 490 $\Omega$) between the two configurations confirms the diode’s ability to rectify (pass current in one direction and block it in the other). Therefore, the diode is functioning properly. *** ### Why Other Options Are Incorrect **A) the diode is intermittently open:** An intermittent open would cause highly unstable or erratic readings, likely fluctuating between very high resistance (open) and a measurable value. The stable, differential readings of 4.7 $\Omega$ and 490 $\Omega$ do not indicate an intermittent failure. **C) the diode is shorted:** A shorted diode acts like a piece of wire and would show very low resistance (approaching 0 $\Omega$) in *both* the forward and reverse directions. Since the reverse reading (Figure B) is 490 $\Omega$, which is significantly higher than the forward reading (4.7 $\Omega$), the diode is not shorted. **D) the diode is open:** An open diode acts like a broken circuit. It would show extremely high resistance (often reading "OL" - Over Limit, or Megaohms) in *both* the forward and reverse directions. Since the forward reading (Figure A) is a very low 4.7 $\Omega$, the diode is clearly not open.