# Diode characteristics/dealing with infinity

• DanDavies
In summary, the conversation discusses a physics assignment involving a simple experiment to increase voltage in a circuit and measure the current/voltage across a diode in forward and reverse. The issue of dealing with infinity in some of the calculations for uncertainty is addressed and various equations are provided for calculating uncertainty in voltage, current, and resistance. The conversation also delves into the aim of the experiment and the best way to present results, including using error bars on a graph. The concept of "infinite" resistance in a diode is discussed and the importance of the forward current and resistance is highlighted. The conversation concludes with a suggestion to measure the slope on a graph to find the value of resistance at a specific point
DanDavies
New to the forum, I'll say "Hi," first :)

## Homework Statement

Have a physics assignment to hand in. Very simple experiment - increase the voltage in a circuit and measure the current/voltage across the diode in forward and reverse. The problem comes with dealing with infinity in some of the calculations for uncertainty.

It's really only the data where the current reads as 0A I have issues with (Right before the P-N junction starts to allow a current to flow, and all the results for a reverse-biased diode). I've written them as follows due to division by zero's. The question really is "Is this the correct way I'd write this?"

## Homework Equations

Uncertainty (Voltage) = Minimum readable voltage (0.01V) / Voltage observed
Uncertainty (Current) = Minimum readable current (0.01A) / Current observed
Uncertainty (Resistance) = Uncertainty (V) + Uncertainty (I)

## The Attempt at a Solution

Voltage: 0.38
Voltage Uncertainty: ±2.63%
Max Voltage: 0.39
Min Voltage: 0.37
Current: 0.00
Current Uncertainty: ±∞%
Max Current: 0 < ∞
Min Current: 0.00
Resistance: 0 < ∞
Resistance Uncertainty: ±∞%

Any suggestions are appreciated.

Last edited:
DanDavies said:
New to the forum, I'll say "Hi," first :)

## Homework Statement

Have a physics assignment to hand in. Very simple experiment - increase the voltage in a circuit and measure the current/voltage across the diode in forward and reverse. The problem comes with dealing with infinity in some of the calculations for uncertainty.

It's really only the data where the current reads as 0A I have issues with (Right before the P-N junction starts to allow a current to flow, and all the results for a reverse-biased diode). I've written them as follows due to division by zero's. The question really is "Is this the correct way I'd write this?"

## Homework Equations

Uncertainty (Voltage) = Minimum readable voltage (0.01V) / Voltage observed
Uncertainty (Current) = Minimum readable current (0.01A) / Current observed
Uncertainty (Resistance) = Uncertainty (V) + Uncertainty (I)

## The Attempt at a Solution

Voltage: 0.38
Voltage Uncertainty: ±2.63%
Max Voltage: 0.39
Min Voltage: 0.37
Current: 0.00
Current Uncertainty: ±∞%
Max Current: 0 < ∞
Min Current: 0.00
Resistance: 0 < ∞
Resistance Uncertainty: ±∞%

Any suggestions are appreciated.

You should be plotting the values of V and I on a graph. You can express the uncertainty in the readings using error bars. Draw the best line through the points.
What are you trying to calculate? You only need percentage errors if you use a formula with data in it that has been measured to a known level of precision.
What is the aim of the experiment? If it is to calculate resistance, that can be found from the gradient of the graph.

Stonebridge said:
You should be plotting the values of V and I on a graph. You can express the uncertainty in the readings using error bars. Draw the best line through the points.
What are you trying to calculate? You only need percentage errors if you use a formula with data in it that has been measured to a known level of precision.
What is the aim of the experiment? If it is to calculate resistance, that can be found from the gradient of the graph.

Sorry I do try to be clear but have a tendency to create the opposite effect :)

The criteria I have to obtain is simple itself - I just wanted to ensure that the way I am presenting my results is correct. Using the example data I posted

$$R=\frac{V}{I}=\frac{0.38}{0}=$$∞

But I know resistance isn't infinate in reality, so I wanted to make that clear in my results. So would R=0<∞ be the correct way to display that?

The criteria for this particular piece of work is to calculate and explain the resistance of a component in a complete circuit, and to describe the relationship of current, voltage, resistance and temperature on macroscopic and microscopic levels.

Also: Whilst on the subjects of charts... Excel isn't that great - especially when I'm trying to plot a diode in revers and forward on the same chart (given that V/I are positive in both directions...) Anyone know something that will do the job?

As I said, if you are varying V and measuring I, you calculate the resistance from the slope of the graph.
A resistance of infinity is not crazy if it refers to the fact that, despite the applied voltage, no current flows. This happens in a diode!
It's not particularly useful to worry about the value of R when in reverse connection. No current means, in practice, infinite resistance.
The forward current and resistance is more important.

I tend to worry about the little things! You've been helpful, I'll leave it as infinity.

The I/V curve is nonlinear, so I'll have to lookup the calculations for the resistance (Havn't been taught it, yet) and try to apply it to my results!

This type of question is more about investigating how the current varies with voltage.
True it isn't linear. The graph is what is important. It should show that there is no current in the reverse direction. The "infinite" resistance is really only a way of stating that mathematically. It's not something you calculate as such.
The forward resistance clearly varies with current. V/I at any point will give its value at that point. It's usual, if you have such a graph, to measure the slope at the point you are interested into find the value of R at that point. If you draw the "best" slope and also a "worse" slope (one that fits but is not so good, yet could reasonably fit) - you can quote the answer as "best" and give the "worst" value as a measure of the uncertainty.
eg if best value gives 50 and worst value gives 55
Quote value as 50 +/- 5

## 1. What is a diode and how does it work?

A diode is an electronic component that allows current to flow in only one direction. It is made up of a semiconductor material with two terminals - an anode and a cathode. When a voltage is applied to the anode, it allows current to flow through the diode, but when the voltage is reversed, it blocks the flow of current.

## 2. What are the key characteristics of a diode?

The key characteristics of a diode include its forward voltage drop, reverse breakdown voltage, and maximum current rating. The forward voltage drop is the minimum voltage required for the diode to start conducting current, while the reverse breakdown voltage is the maximum reverse voltage that the diode can withstand before it starts conducting in reverse direction. The maximum current rating is the maximum amount of current that the diode can handle without getting damaged.

## 3. How does a diode behave when dealing with infinity?

When a diode is dealing with infinity, it behaves as an open circuit. This means that no current will flow through the diode, regardless of the voltage applied. This is because the reverse breakdown voltage of a diode is typically very high, making it impossible for any practical voltage to cause the diode to conduct in reverse direction.

## 4. How can I protect a diode from infinity conditions?

To protect a diode from infinity conditions, a reverse-biased diode or a zener diode can be used. These diodes are designed to withstand high reverse voltages and can be connected in parallel with the diode being protected. This will allow the excess voltage to be safely bypassed, protecting the diode from potential damage.

## 5. How do I select the right diode for a specific application?

To select the right diode for a specific application, you need to consider the voltage and current requirements of the circuit. You should choose a diode with a forward voltage drop that is lower than the operating voltage of the circuit and a maximum current rating that is higher than the expected current. You should also consider the switching speed and temperature requirements of the circuit to ensure that the diode can operate efficiently and reliably.

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