How do you solve PSLE Science light-and-shadow questions when the light source, object or screen moves? First identify where light begins, which object blocks its straight-line path and where the shadow is observed. If the object moves nearer the light while the screen stays fixed, its shadow often becomes larger in a simple single-source setup. If an extra torch is switched on, the number, position and darkness of shadows may change. The diagram, not a memorised slogan, decides the answer.
MOE teaches Light at Primary 4, and the 2023 Primary Science syllabus specifically includes objects seen by emitting or reflecting light, light travelling in straight lines, shadows formed by complete or partial blockage, and variables such as source–object and object–screen distance. This remains part of cumulative Standard PSLE Science preparation in Primary 6. SEAB’s verified 2026-onward Standard Science (0009) format is 30 MCQs worth 60 marks plus 10–11 structured questions worth 40 marks in one 105-minute written paper.
This guide teaches one repeatable method for exam diagrams, then gives 28 original worked examples, simple drawing checks and a revision routine. The official syllabus says neither the law of reflection nor compulsory use of the terms transparent, translucent and opaque is required; pupils still need to understand how objects transmit or block light under the conditions supplied. Nothing here predicts the unseen 2027 paper.
- Identify the source: a torch, lamp or Sun emits light; ordinary books and tables are seen when they reflect it.
- Draw straight lines: a shadow forms where light is blocked.
- Check distances: identify what moved and what stayed in place before predicting size.
- Check object shape: a rotated object can cast a different silhouette.
- Check sources: two torches can produce multiple illuminated and shadowed regions.
- Check reflection: mirrors redirect light, but an advanced reflection formula is not a Primary Science requirement.
- Explain evidence: state what the diagram supports and avoid treating every dark region as the same.
Official syllabus scope and what to prioritise
The MOE 2023 Light topic at Primary 4 expects pupils to recognise that objects can be seen if they give out light or reflect light towards an observer. It recognises straight-line travel of light and shadow formation when light is completely or partially blocked. Pupils investigate shadow shape, size and position and the effects of source–object and object–screen separation. This gives a clear roadmap for what needs to be practised.
The official note says learning a law of reflection is not required. The syllabus also says the specialised labels transparent, translucent and opaque are not compulsory. That does not remove the underlying idea that some materials let more light through than others. A child should be able to explain why a clear sheet and a thick piece of cardboard produce different shadow effects without needing unnecessary jargon.
The aim is interpretation. A ray diagram may be drawn vertically, horizontally or diagonally, and a light source may be large rather than a tiny point. Reliable answers use the lines, obstacles and shaded regions shown. A picture that looks familiar can still contain a different arrangement with a different outcome.
Source, object, screen: the three-part shadow model
In a simple torch experiment, light travels from the torch towards a screen. Put a non-transmitting object in between, and some rays cannot reach parts of the screen. The region receiving less or no light appears as a shadow. Its outline reflects the shape of the object as seen from the light source, as well as the geometry of the arrangement.
The school-style diagram often assumes one small light source and one screen. Under that idealised arrangement, rays can be drawn from the source past the edges of the object to the screen. The boundary between illuminated and shadowed regions follows those paths. If the object moves closer to the source while the screen remains at the same place, the projected silhouette generally becomes larger.
Real torches may emit light from a finite area rather than a mathematical point. That can create partially shadowed edges. Rather than pretending every shadow must be perfectly sharp, read the question’s source type and conditions. The underlying Primary Science skill is still understanding where light travels and what blocks it.
Shadow size depends on what actually moved
If the light source and screen remain fixed, bringing the object nearer the source generally enlarges its projected shadow in the simple point-source model. Moving the object nearer the screen generally makes the shadow smaller and closer to the object’s actual size. If the source and object remain fixed while the screen moves farther away, the projected shadow generally becomes larger.
Those statements have controlled conditions. If a pupil moves the source and screen simultaneously, or changes the object’s orientation while moving it, the observation cannot automatically be attributed to a single distance. The question may be testing whether the student noticed which variable changed. Identify that variable before applying the size rule.
A correct conclusion should name the comparison: ‘The object’s shadow became larger when it moved nearer the light source while the screen remained fixed.’ A weak conclusion says ‘closer means bigger’ without saying closer to what. The vague phrase can be used incorrectly when the diagram changes.
Why shape and position can change independently of size
Imagine a flat rectangular card held face-on to the light. Its shadow may look rectangular. Rotate the card edge-on, and the projected shape can become much narrower even though the card itself has not physically shrunk. This is why shadow shape and shadow size should be considered separately. Shape depends on orientation as well as the object’s outline.
Moving the light source sideways can shift the shadow position across the screen. This is not equivalent to rotating the object. A child might correctly predict a sideways movement but incorrectly describe it as the object becoming shorter. Good answers identify which part of the observation changed: shape, size, location or darkness.
Seeing objects: emit light versus reflect light
The Sun, a switched-on light bulb and a luminous torch are light sources. A book, an unlit spoon and the Moon are commonly seen because light falls on them and is reflected towards our eyes. The Moon does not produce the visible sunlight it reflects. Reflection is therefore an everyday reason an object can be seen.
Students often say ‘you can see a book because the book has light’. A more accurate explanation is that light from a source falls on the book and some light is reflected towards the observer. If there is no suitable light reaching the book and then the eye, it cannot be seen in the ordinary visual sense. A mirror changes the direction of light, but the pupil does not need to memorise the numerical angle law to grasp this.
Two torches: why shadows can multiply
Suppose one object stands between a screen and two separated torches. Each torch casts its own pattern of blocked light. Parts of the screen may be lit by both, by only one or by neither. The object can therefore produce more than one shadow or regions of different darkness, depending on the source positions and brightness. This can confuse pupils expecting a single solid black silhouette.
The reliable method is to analyse one source at a time. Pretend Torch B is off; draw the region Torch A cannot illuminate. Then pretend Torch A is off and trace the region blocked from Torch B. Combine the two patterns: where neither light reaches the screen, it is darker; where one still reaches, the region may be partly illuminated. This is a simple model and should be adjusted if the question includes other light sources.
A second torch does not make the object produce a second physical copy of itself. It changes the light paths. Likewise, a screen’s apparent shadow may shift when the source shifts even if the object is stationary. Distinguish object movement from shadow movement throughout the explanation.
Twenty-eight original PSLE-style worked questions
1. What is a light source?
Original question: Which emits its own visible light: a lit torch or an ordinary unlit book?
Worked answer: The lit torch.
Reasoning: The book is normally seen by reflected light rather than its own emission. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Would the unlit book become invisible in complete darkness? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
2. Seeing the Moon
Original question: Is the Moon a light source in the same sense as the Sun?
Worked answer: No. We see the Moon mainly because it reflects light from the Sun.
Reasoning: A visible object does not necessarily emit its own light. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What would happen if no sunlight could illuminate the Moon? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
3. Seeing a mirror
Original question: Why can an observer see a bright reflection in a mirror?
Worked answer: Light from a source is reflected by the mirror towards the observer.
Reasoning: The mirror redirects light; it need not generate light. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the reflected path does not reach the observer’s eye? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
4. A cardboard shadow
Original question: An opaque piece of cardboard blocks light travelling to a screen. Why is a dark region formed?
Worked answer: The cardboard blocks the direct light that would otherwise reach that part of the screen.
Reasoning: The source–object–screen route determines the blocked region. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What happens if the cardboard is removed? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
5. One straight ray
Original question: A torch shines towards an object. Can a ray simply bend around the object without an optical effect shown?
Worked answer: No. Under the simple school model, light travels in straight lines.
Reasoning: Do not invent curved paths to make a wrong answer fit. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: How should boundary rays be drawn around the object’s edges? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
6. Object nearer source
Original question: With torch and screen fixed, a small card moves nearer the torch. What happens to its simple point-source shadow?
Worked answer: The projected shadow generally becomes larger.
Reasoning: The card intercepts a wider spread of rays relative to the screen. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the card moves nearer the screen instead? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
7. Object nearer screen
Original question: With light and screen fixed, a card moves closer to the screen. Predict the shadow size.
Worked answer: It generally becomes smaller in the simplified setup.
Reasoning: State the reference points rather than saying ‘closer makes smaller’ universally. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Would its shadow disappear merely because it approaches the screen? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
8. Screen farther away
Original question: The torch and card stay fixed while the screen moves farther behind the card. What happens to shadow size?
Worked answer: It generally becomes larger with increased projection distance in a point-source model.
Reasoning: The moving object is the screen, not the card. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the screen moves nearer the card? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
9. Sideways source
Original question: A torch moves left while the object and screen remain fixed. Can the shadow move across the screen?
Worked answer: Yes. Changing the light direction can move the shadow position.
Reasoning: A shadow can move even when the object stays still. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Which changed variable should be named? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
10. Rotated card
Original question: A rectangular card rotates from face-on to nearly edge-on. Could its shadow become narrower?
Worked answer: Yes. Its projected shape and width can change with orientation.
Reasoning: The card’s physical dimensions have not changed. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the card returns to its original orientation? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
11. Two light sources
Original question: Two separate torches illuminate one object. Must there be only one shadow?
Worked answer: No. Each source can cast its own shadow pattern.
Reasoning: Analyse the sources separately before combining the regions. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if one torch is switched off? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
12. Overlapping dark regions
Original question: Two shadow patterns overlap on a screen. Which region may be darkest?
Worked answer: The region blocked from both light sources can be darker than a region still illuminated by one source.
Reasoning: The explanation depends on how many sources can illuminate each point. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the torches have different brightness? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
13. Extra torch switched on
Original question: A student turns on Torch B while Torch A stays on. Does this necessarily make every point of the screen darker?
Worked answer: No. Adding an illuminating source can brighten regions; the patterns of shadows depend on geometry.
Reasoning: An additional light source adds light rather than automatically producing darkness everywhere. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Trace which regions are still blocked from each source. Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
14. Clear sheet
Original question: A clear sheet lets much of the light through. Must it cast the same dark shadow as thick cardboard?
Worked answer: No. A material that transmits much of the light may produce a weaker or different shadow.
Reasoning: The amount of light transmitted matters more than memorising a specialist label. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the clear sheet is replaced by a thick non-transmitting card? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
15. Partly transmitting sheet
Original question: A cloudy plastic sheet allows some light through but scatters it. Will its shadow necessarily match solid cardboard?
Worked answer: Not necessarily. Some light can still reach the screen, making a less dark shadow.
Reasoning: Partial blockage differs from complete blockage. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What change in the observed region would support this distinction? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
16. Source too far to one side
Original question: A torch points away from the object. Must the object cast a shadow on the given screen?
Worked answer: No. The relevant light may not encounter the object and screen in the required arrangement.
Reasoning: Read the direction of light rather than the existence of a torch. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: How could the source be repositioned to form a shadow? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
17. Object off the beam
Original question: A small card is moved completely outside the torch’s light beam. What happens to its shadow on the screen?
Worked answer: The card no longer blocks that beam, so its shadow from that beam disappears.
Reasoning: An object must block relevant light to cast that particular shadow. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if a second torch points at the card from another direction? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
18. Larger object
Original question: The original card is replaced by a wider card at the same location. What happens to the shadow in a comparable setup?
Worked answer: A larger silhouette is generally projected, producing a wider shadow.
Reasoning: The object changed rather than the distance. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the object also rotates? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
19. Source-object distance fair test
Original question: Two trials use different cards and different source distances. Can a shadow difference be attributed only to distance?
Worked answer: No. Card size is a competing variable.
Reasoning: A fair test changes the intended distance while keeping the object and other conditions comparable. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: How would you redesign the comparison? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
20. Screen distance fair test
Original question: A pupil changes screen distance but uses two torches of different size in the trials. Is that a clean test?
Worked answer: No. Source characteristics also changed.
Reasoning: One observation cannot isolate screen distance when other relevant factors differ. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What should be held constant? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
21. Measured shadow width
Original question: A shadow width changes from 12 cm to 18 cm. What is the increase?
Worked answer: 6 cm.
Reasoning: Read the same dimension at both times and subtract. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Would the result alone show which component moved? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
22. Relative size
Original question: Shadow A is 20 cm wide and Shadow B is 15 cm wide. Does that prove Object A is physically larger?
Worked answer: No. Shadow size also depends on the light, object and screen arrangement.
Reasoning: Do not infer an object’s actual size from the shadow alone. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What extra measurements would make a comparison more meaningful? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
23. Shadow movement
Original question: A fixed pole’s shadow changes position during the day. Does that imply the pole moved?
Worked answer: No. The apparent direction of sunlight changes as Earth rotates, shifting the shadow.
Reasoning: Changing illumination can alter a shadow without movement of the object. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Can the shadow be used as a rough indicator of time? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
24. Light passing an opening
Original question: A screen has a small opening and a torch shines through it. What path is expected in the simple model?
Worked answer: Light travels along straight paths through the opening.
Reasoning: A hole changes which rays pass, not the basic straight-line property. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if an object blocks the opening? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
25. Object with a hole
Original question: A card contains a small hole. Can a light spot appear within an otherwise shadowed region?
Worked answer: Yes, light can pass through the hole to the screen if the paths align.
Reasoning: A shadow need not have uniform darkness across its entire area. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Would shifting the torch change where that bright spot appears? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
26. Mirror reroutes light
Original question: A mirror reflects a beam towards a wall that the original direct path did not reach. What process is involved?
Worked answer: Reflection changes the direction of light.
Reasoning: The mirror is not necessarily a light source itself. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: Must Primary pupils calculate angles of incidence to describe the reflection? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
27. The ‘always bigger’ claim
Original question: A pupil claims moving any object closer to any screen always enlarges its shadow. Is that justified?
Worked answer: No. The effect depends on the source–object–screen geometry and what remains fixed.
Reasoning: A simple model’s rule must not be copied into a different arrangement without conditions. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: State the correct controlled rule for a single small source. Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
28. Reconstruct the experiment
Original question: A diagram shows the same card at two distances with one torch and fixed screen. One shadow is larger. What conclusion could be supported?
Worked answer: Under the idealised conditions, the larger shadow corresponds to the card being nearer the light source.
Reasoning: The inference depends on the identical object, source and screen arrangement. Identify which path was blocked and which part of the setup changed; do not give an unsupported ‘always’ statement when the diagram may use different conditions.
Transfer: What if the object shape or orientation also changed? Solve the altered case independently, then say which variable determines whether the earlier explanation still applies.
A practical four-step drawing method
- Mark each source and the direction in which it illuminates the scene.
- Identify the edges of the object that can block the relevant straight-line paths.
- Trace the boundary of the blocked region to the screen; inspect whether there is one source or more.
- Name the observed change in shape, size, position or darkness, using the appropriate source–object–screen relationship.
A child should be able to draw rough boundary lines without needing perfect artistic skill. The diagram is a thinking aid. If the setup has two torches, cover one drawing at a time and combine the results. If the object rotates, show its new projected outline. If the screen moves, draw the same light paths extending to the new position.
The method also guards against a common error in the written answer: a student says ‘the object moved and caused the shadow’ when the light source actually moved. Name the changed component accurately. When the question asks for a suggested fair test, use the same object, same light source and same screen while changing only the intended distance.
How to describe results and evaluate experiments
Suppose a table records shadow widths at different object positions. A description should use the actual observed trend and units. An explanation can then connect distance to the spread of blocked light under the stated single-source conditions. A conclusion that one distance ‘always produces the largest shadow for every object and lamp’ is stronger than the evidence and should be corrected.
If the results do not follow the expected simplified trend, inspect whether the torch position changed, whether the object rotated, or whether a ruler was read from an incorrect angle. Repetition may show whether a result is consistent, but repeated use of the same flawed setup will not correct an uncontrolled variable. Distinguish evidence from expectation rather than deleting a surprising measurement.
Seven high-frequency misconceptions worth repairing
- A mirror makes its own light — it reflects incoming light.
- The Moon is a light source just like the Sun — its visible light is reflected sunlight.
- Every object casts an equally dark shadow — the amount of light transmitted or blocked matters.
- A shadow always becomes bigger when anything moves closer — the reference point and other fixed components matter.
- A second torch always erases all shadows — multiple sources can produce multiple dark and partly illuminated regions.
- The law of reflection must be memorised for this P4 topic — MOE explicitly says it is not required.
- A fixed object cannot produce a moving shadow — changing illumination can move a shadow.
A two-week study routine
- Day 1: identify emitting and reflecting objects with six examples.
- Day 2: practise straight-line rays and the source–object–screen sequence.
- Day 3: move only the object and predict shadow size.
- Day 4: move only the screen and compare with Day 3.
- Day 5: rotate objects and separate shape from size.
- Day 6: analyse two torches source by source.
- Day 7: attempt mixed original questions and log error types.
- Day 8: retry wrong explanations without notes.
- Day 9: investigate reflected light with safe classroom materials.
- Day 10: compare clear and blocking materials without relying on technical labels.
- Day 11: complete fair-test design questions.
- Day 12: interpret a shadow-size data table.
- Day 13: complete a timed short MCQ and structured set.
- Day 14: solve changed scenarios and explain what stayed constant.
A parent can safely illustrate these ideas with a desk lamp, cardboard and a wall under ordinary conditions, avoiding direct viewing of bright light sources, lasers or electrical modifications. The lesson should focus on observation, evidence and cause rather than a spectacular visual effect. For a strong pupil, use two lights and a changed screen position; for a struggling pupil, use one source and one object first.
Frequently asked questions
Are light and shadows examinable at PSLE if first taught in P4?
They are part of the cumulative Primary Science syllabus. Primary 6 students should understand source–object–screen diagrams and apply the learning to unfamiliar contexts.
Does light travel in straight lines?
The Primary Science syllabus treats straight-line travel of light as the basis of shadow formation. Use that simple model for the diagrams unless other effects are explicitly introduced.
Does the shadow get bigger when the object moves closer to the light?
In a simple one-source model with the source and screen fixed, the shadow generally grows as the object moves nearer the source. State the controlled conditions.
Why can two torches make two shadows?
Each torch has its own blocked-light region. Different source positions can produce different patterns and overlap regions.
Do students need the law of reflection?
No. The MOE Primary Four Light syllabus states that the law of reflection is not required.
Must pupils use transparent, translucent and opaque?
The syllabus explicitly says compulsory use of those labels is not required. Understanding whether an object blocks or lets light through is more important.
Do these diagrams guarantee what appears in PSLE 2027?
No. The diagrams are original applications of published learning outcomes, not predictions or secret examination materials.
What is the fastest repair for repeated shadow errors?
Make the pupil name the source, object, screen and only the part that moved, then trace the blocked paths. Change one condition after the correction.
Official sources and further reading
- MOE: 2023 Primary Science syllabus — P4 Light and shadow investigations
- SEAB: 2026 revised PSLE subject formats
- SEAB: Standard PSLE Science 0009 official format
- eduKate: PSLE light, shadow size and reflection preparation
- eduKate: two-torch and mirror diagram traps
- eduKate: fair-test interpretation
- eduKate: PSLE Science syllabus hub
Editorial check, 12 November 2026. Every question is original teaching material and not an official paper or forecast of the 2027 examination. The published MOE syllabus and currently verified SEAB format are the study references.