For many years, while teaching Characteristics of Image Formed by a Convex Lens, I held a firm belief:
students should not be taught to memorise image characteristics based on object distance.
Instead, I consistently emphasised the importance of drawing ray diagrams, observing the outcome, and concluding the nature of the image. To me, this approach represented true physics learning—reasoning over rote learning, understanding over recall.
And I still believe this approach is fundamentally correct.
However, a recent moment of personal “stuckness” forced me to re-examine my stance more honestly.
One day, while explaining a question spontaneously, I realised that I had momentarily forgotten the exact light ray pathway. The ray diagram did not flow naturally from my thinking. In that brief pause, something became very clear to me:
Without internalised memory of basic ray rules, understanding itself cannot even begin.
This experience reshaped my perspective.
Understanding and Memorisation Are Not Opposites
In physics education, we often present memorisation and understanding as opposing forces. But classroom reality tells a more nuanced story.
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Ray diagrams are tools for reasoning.
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But reasoning requires something to work with.
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That “something” is minimum necessary memory.
If students do not firmly remember the three principal rays of a convex lens, then asking them to “draw and conclude” becomes an empty instruction. The diagram collapses before it is even constructed.
The issue, therefore, is not whether students memorise—but what and how they memorise.
What Should Be Memorised (and What Should Not)
Through reflection, I now distinguish clearly between two levels of learning:
❌ What students should NOT memorise
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“If the object is here, the image must be like this.”
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Lists of outcomes detached from reasoning.
These are end results, not thinking processes.
✅ What students MUST memorise
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The three principal ray rules:
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Parallel ray refracts through the focal point.
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Ray through the focal point emerges parallel.
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Ray through the optical centre travels undeviated.
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These rules must be so familiar that they are recalled automatically, without cognitive strain.
Only then can ray diagrams function as a thinking tool rather than a burden.
A Refined Teaching Flow
From this reflection, I now consciously emphasise the following sequence to students:
Ray Diagram → Observe → Conclude → Mnemonic CHECK
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Ray Diagram: Constructed using memorised ray rules
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Observe: Identify real/virtual, inverted/upright, size
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Conclude: Justify the image characteristics
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Mnemonic CHECK (e.g. RID–RIS–RIM–VUM): Used only to verify, not replace thinking
This final “check” stage is important. Mnemonics are not the enemy of understanding; they are safety nets that reduce careless errors and build student confidence—especially under exam pressure.
A Shift in My Own Teaching Philosophy
I now tell my students openly:
“Memory starts the thinking; ray diagrams complete the understanding.”
This statement reflects my current belief as a physics educator. Memorisation is not a shortcut around thinking—but a key that unlocks it.
As teachers, especially those preparing students for SPM, our role is not to choose between understanding and memory, but to orchestrate both deliberately. When done well, memorisation supports reasoning, and reasoning gives memorisation meaning.
This reflection has reminded me that even as experienced teachers, our teaching philosophies must remain flexible, honest, and classroom-tested.
And sometimes, it takes getting stuck ourselves to see more clearly how our students feel.
