Linking gradient of IV graph and resistance

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."
  • #1
MBBphys
Gold Member
55
0

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!

Homework Equations


V=IR

The Attempt at a Solution


N/A
 
Physics news on Phys.org
  • #2
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!

Homework Equations


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?
 
  • #3
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
    215.4 KB · Views: 277
  • #4
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: 281
  • #5
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
    Capture.PNG
    50.5 KB · Views: 558
  • #6
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".
 

Related to Linking gradient of IV graph and resistance

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.

Similar threads

Gradients of Graphs with and without Rates of Change
    • Introductory Physics Homework Help
Replies
19
Views
1K
Why is the gradient of a V-I graph equal to resistance for ohmic materials?
    • Introductory Physics Homework Help
Replies
2
Views
2K
How to determine the change of resistance from I-V graph?
    • Introductory Physics Homework Help
Replies
9
Views
2K
Resistance of a non-ohmic device from its I/V graph
    • Introductory Physics Homework Help
Replies
10
Views
3K
Finding the smallest resistance on a I-V graph
    • Introductory Physics Homework Help
Replies
8
Views
3K
Potential Gradient of potentiometer wire
    • Introductory Physics Homework Help
Replies
2
Views
4K
Which equation is used to define resistance?
    • Introductory Physics Homework Help
Replies
10
Views
1K
How does the gradient of the graph compare to the W force
    • Introductory Physics Homework Help
Replies
3
Views
4K
Was there a mistake in our final exam question about resistance?
    • Introductory Physics Homework Help
Replies
30
Views
2K
Equivalent resistance of a circuit
    • Introductory Physics Homework Help
Replies
3
Views
1K

Hot Threads

Recent Insights

Back
Top