A variable dc power supply having reversible polarity is...

A variable dc power supply having reversible polarity is connected to a diode having a $p - n$ junction as shown in Figure 29.28 Starting with the power supply's polarity as shown in gradually decreased to zero gradually decreased to zero and then gradually increased in the reverse direction. (a) Sketch a graph of the reading in the ammeter as a function of the potential difference $V$ across the power supply. Make sign differences clear. (b) Suppose now that the terminals of the diode are reversed and the same procedure is followed. Sketch a graph of the reading in the ammeter as a function of the potential difference $V$ across the power supply. Make sign differences clear. (c) Suppose now that the diode is replaced by an ordinary resistor and the same procedure is followed. Sketch a graph of the reading in the ammeter as a function of the potential difference $V$ across the power supply. Make sign differences clear. (d) Explain the reasons for the differences between the graphsin (i) parts (a) and (b), (ii) parts (a) and (c).

Key Concepts

P-N Junction Diode Behavior

A p-n junction diode has a nonlinear current-voltage relationship. In forward bias, when the applied voltage exceeds the intrinsic barrier or threshold voltage, the diode begins to conduct significantly, with current rising rapidly. In reverse bias, only a very small leakage current flows until the reverse breakdown voltage is reached, though standard diodes are designed to avoid breakdown in normal operation.

I-V Characteristics of Nonlinear Devices

The current-voltage (I-V) characteristic of a diode is distinctly nonlinear. For forward bias, the I-V curve shows little current until a specific threshold is reached, after which the current increases dramatically. In contrast, a resistor has a linear I-V relationship (

Transcript

00:01 I'm just going to jump into part a for 26, because i assume you have read the rest, but we want to start out by sketching a graph, which is always a good idea to get an idea for the physics of the situation.

00:18 And we are going to be sketching a graph of the ammeter as a function of the potential difference, the voltage, across the power supply.

00:27 So the current versus voltage graph for our different, let's see, draw it like this.

00:56 For part a in the situation that we have, like in the configuration shown, you're going to get something like this.

01:07 So you have a negative voltage, zero, there's a crossing point, and then we increase like this.

01:14 So you have that saturation current at negative voltages going there in the opposite direction.

01:24 But then part b asks for the situation when the terminals of the diode are reversed and the same procedure is followed.

01:34 So look at the ammeter as a function of voltage across the power supply.

01:39 Well, it is quite a bit different now because you have switched the polarity of the diode.

01:45 So now it's almost just the inverse of that one.

02:01 And there's some saturation here.

02:05 So it goes off to infinity in the negative way.

02:10 So you see the similarity between this one and this one.

02:14 They're just sort of like flipped, i guess.

02:18 But part c, we want to just take the diode out, put in a normal resistor, and do the same thing.

02:28 Now, this one is a lot easier because there is a result.

02:33 Resistor has no dimensional component to it.

02:36 It doesn't matter which way it's flowing.

02:40 Oh, no, i've been a bad boy.

02:42 Let's replace this here.

02:45 There we go.

02:45 Label our graphs...

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