SPM Physics: AHA! Graphs – Intercept Revealed by Linear Form!

 

In graph questions, many students guess the intercept by intuition. That’s a trap. The intercept is revealed only when the equation is rearranged into linear form and compared with

$y=mx+c$

.

Example (Lens Equation + Magnification):

• Magnification:
  $m=\frac{v}{u}$

• Lens equation:
  $\frac{1}{v}=\frac{1}{f}+\frac{1}{u}$

• Rearrange:
  $v=fm+f$

Compare with straight line:

$$y=mx+c$$

Gradient =

$f$

Intercept =

$f$

Therefore, the intercept represents the focal length.

Exam traps:

• Choosing object distance instead of focal length.

• Guessing without rearranging.

• Forgetting to match with
  $y=mx+c$
  .

Success flow: Formula → Rearrange → Linear form → Compare → Identify intercept → Score marks.

AHA! Don’t guess, derive. Not by sight, but by INSIGHT!

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