The Definition of Resistance Pt 2

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Can see Physics in a PET bottle used for carbonated drinks? Two days ago some of the students in my school are busy designing water rockets from used PET bottles. Yesterday was the Co-curriculum Day in my school. One of the highlights is the Water Rocket Competition organised by the panel of Physics teachers.
Back to the definition of resistance. Can resistance be also defined as the gradient of the V-I graph?
Consider Fig. 2, which shows the V-I relationship for two conductors X and Y. If resistance can be defined as the gradient of the V-I graph, then at current i, the resistance of Y is greater than X. If resistance is the ratio V/I, then at current i, both X and Y have the same resistance. So what does this show?
You cannot in general say that resistance is equal to the gradient of the V-I graph. This is only true for ohmic conductors.
In the Malaysian SPM 2006 Physics Paper 3, there is a question which gives a V-I graph as shown in Fig. 3.
The question goes on to say, "The gradient of the graph represents resistance. State how resistance varies with current."
In the light of what has been discussed, what do you have to say? If we leave out the first sentence in the question, "The gradient ..... ", can the question still be answered?
Bye for now.

Anonymous said...

Hi Koay, proud to see you joining the blogger group! Titles and topics of discussion are very relevant! Will recommend strongly to my circles of friends!

April 30, 2008 3:36 PM

Thinking Allowed said...

Hei! Koay. Glad that you are sharing your expertise with everyone. Physics is fun. But not everybody sees it that way. Hope you can show them how.

April 30, 2008 11:29 PM