Why Might Plotting log c Against log d Not Be the Best Test for Proportionality?

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Homework Help Overview

The discussion revolves around the proposal that variable c is proportional to d raised to the power of 0.5. Participants are exploring suitable graphical representations to test this relationship, particularly focusing on logarithmic transformations.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the validity of plotting log c against log d to test the proportionality claim. There is confusion about the implications of the proposed relationship and the correct form of the logarithmic equation. Some participants suggest that constants in proportionality may have been overlooked.

Discussion Status

The discussion is ongoing, with participants expressing uncertainty about the mark scheme's requirements and the correctness of their proposed equations. There is no explicit consensus, but several lines of reasoning are being explored regarding the nature of the relationship between c and d.

Contextual Notes

Participants are grappling with the definitions of direct versus inverse proportionality and the implications of constants in the proportionality relationship. The mark scheme's acceptance of a different equation is also under scrutiny.

Peter G.
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Hi,

The question is the following:

Another student proposes that c is proportional to d0.5 State a suitable graph that can be plotted to test this proposal.

I suggested plotting log c = 0.5 log d.

One of the answers the markscheme accepts is log c = log d

Can anyone tell me why my answer is wrong?

Thanks!
 
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Peter G. said:
Hi,

The question is the following:

Another student proposes that c is proportional to d0.5 State a suitable graph that can be plotted to test this proposal.

Inversely proportional or directly proportional ?

I suggested plotting log c = 0.5 log d.

One of the answers the mark scheme accepts is log c = log d

Can anyone tell me why my answer is wrong?

Thanks!

Is c directly proportional to d1/2 ? If so , then equation cannot be log c = 0.5 log d.

Anyways what's precisely is question asking for ? Your answer seems to be wrong because you missed the constants involved in proportionality.
 
It is supposed to be directly proportional I guess, since they want a straight line through the origin.

I just don't understand how you can get lg c = lg d like the mark scheme asks for
 
Peter G. said:
I just don't understand how you can get lg c = lg d like the mark scheme asks for
The mark scheme appears to be wrong. Perhaps the person who wrote it accidentally left out the 0.5 factor.
 

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