TbarAnon
Hey TbarAnon,
I found that they are many questions like the graph ones on the QCAA tests (including the external exams) so I crafted an "ideal" answer for that when I did the QCE last year. Here it is below and for context, it talks about a graph with F=BIL formula.
As seen from the graph, there is a direct and linear relationship between F and I: F∝I. This means the relationship follows y=mx+c. From the graph, it can be seen that the y-intercept is 0 which means that c=0. Let m be the gradient of the graph: m=rise/run=Δy/Δx=ΔF/ΔI=(2.5×10-2)/4=6.25×10-3. Therefore, the mathematical relationship follow the following equation: y=6.25×10-3 x ⇒ F=6.25×10-3 I.
From that, hopefully, that answers all your questions including how long it should be (but usually stick to how many lines they give you in the answer).
TLDR: you have to identify the relationship if its linear, exponential, directly/inverse relationship and then develop an equation for it as well. Then usually, you use that equation to figure out a constant in the next question.
Hope that helps and feel free to ask any other questions.
