• MBBphys
In summary, on a markscheme for an AS level physics paper, there is a penalty for linking gradient to resistance when analyzing a current-voltage graph for a resistor. This is because the preferred answer is to mention the gradient as the way to determine the resistance, and mentioning the gradient alone without linking it to resistance is considered incomplete. Additionally, there is a mistake in the markscheme where the statement "qualification: I increases faster than V" is not valid since I and V have different dimensions. It should instead state "the rate of increase of I with respect to V increases."

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## Homework Statement

If I have a current-voltage (y-x) graph for a resistor, I could argue that the reciprocal of the gradient at a point is equal to the resistance of that resistor at that pd across it.

However, on a markscheme for an AS level physics paper, they penalised linking gradient to resistance in any way whatsoever. Why is that?

Thanks in advance for any help!

V=IR

N/A

MBBphys said:

## Homework Statement

If I have a current-voltage (y-x) graph for a resistor, I could argue that the reciprocal of the gradient at a point is equal to the resistance of that resistor at that pd across it.

However, on a markscheme for an AS level physics paper, they penalised linking gradient to resistance in any way whatsoever. Why is that?

Thanks in advance for any help!

V=IR

## The Attempt at a Solution

N/A
It might help to quote the whole question verbatim. E.g. is it possible there is inductance involved here?

haruspex said:
It might help to quote the whole question verbatim. E.g. is it possible there is inductance involved here?
It's question 1 part c) of the document attached; thanks!

#### Attachments

• 175458-question-paper-unit-g482-01-electrons-waves-and-photons.pdf
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MBBphys said:
It's question 1 part c) of the document attached; thanks!
And the markscheme's attached as well if you wish to see

#### Attachments

• 176278-mark-scheme-unit-g482-electrons-waves-and-photons-june.pdf
166 KB · Views: 274
MBBphys said:
And the markscheme's attached as well if you wish to see
The actual section of the markscheme, with the comment about not accepting link between gradient and resistance highlighted. Thanks :)

#### Attachments

• Capture.PNG
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I believe the author of the mark scheme stuffed up in at least two ways.
In the "do not allow" there is a crucial word missing. It should say "do not allow either of the first two marking points if no reference made linking gradient and R value". The point is that the two options being allowed as variants to the preferred answer are incomplete unless you mention the gradient as the way to determine R.
This is also a blunder: "qualification: I increases faster than V"
Since I and V are dimensionally different, it does not mean anything to say that one increases faster than the other. It should say "the rate of increase of I with respect to V increases".

## 1. What is an IV graph and how is it used to measure resistance?

An IV (current-voltage) graph is a visual representation of the relationship between the current flowing through a circuit and the voltage applied to it. The gradient of this graph represents the resistance of the circuit, with a steeper gradient indicating a higher resistance.

## 2. How do you calculate the gradient of an IV graph?

The gradient of an IV graph can be calculated by dividing the change in voltage by the change in current. This can be done by selecting two points on the graph and using the formula (V2 - V1)/(I2 - I1), where V is voltage and I is current.

## 3. What is the significance of the gradient in an IV graph?

The gradient of an IV graph is directly proportional to the resistance of the circuit. This means that a higher gradient indicates a higher resistance and a lower gradient indicates a lower resistance. By analyzing the gradient, we can determine the resistance of a circuit and make conclusions about its components and behavior.

## 4. How does the gradient change when the resistance of a circuit changes?

As mentioned before, the gradient of an IV graph is directly proportional to the resistance of a circuit. This means that when the resistance increases, the gradient also increases. Similarly, when the resistance decreases, the gradient decreases.

## 5. Can the gradient of an IV graph be negative?

Yes, the gradient of an IV graph can be negative. This occurs when the current and voltage have an inverse relationship, such as in a diode. In this case, the gradient represents the inverse resistance, also known as conductance.

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