For PSLE Science light-and-shadow questions, remember three rules: an object is seen when light from it reaches our eyes; light travels in straight lines; and a shadow appears where an object blocks all or part of the light from a source. For a torch–object–screen experiment, first check which distance changes. If the source and screen stay fixed, moving the object nearer a small light source usually produces a larger shadow on the screen; moving it nearer the screen produces a smaller shadow.
This Primary 6 revision guide covers the light topic from Primary 4, because PSLE Science builds on the concepts taught throughout Primary 3 to 6. The MOE syllabus also covers investigating shadow shape and size as objects and distances change. It does not require the law of reflection or the technical labels “transparent”, “translucent” and “opaque”; understanding how much light a material allows through is the real skill.
The latest official examination format checked for this article is the Standard PSLE Science paper introduced for examination from 2026. A past question style is not a guaranteed 2027 question. Learn the underlying mechanism and practise interpreting unfamiliar diagrams rather than memorising a predicted shadow drawing.
- Fast answer: source of light → object → screen; the shadow forms where light is blocked.
- Seeing: a lit torch produces light; an unlit book is visible because it reflects light into our eyes.
- Shadow direction: the shadow lies on the side away from the light source in the simple setup.
- Shadow size: check both source–object and object–screen distances, not just the diagram’s drawing size.
- Blocking: materials can allow most, some or no light to pass through.
- Exam trap: sunlight and moonlight are not separate sources in the same sense; the Moon reflects sunlight.
- Syllabus boundary: ray-angle law of reflection and terminology-only drills are lower priority than the named learning outcomes.
Reference: MOE Science Teaching & Learning Syllabus, updated May 2024, page 75 (P4 Light) and SEAB 2026 PSLE paper formats. This is an independent teaching guide, not an official examination prediction.
Quick navigation
- How people see objects
- Straight-line travel of light
- Source, object and screen
- How distance changes shadow size
- Most, some or no light
- Data and fair tests
- 20 original worked questions
- A four-week learning plan
- FAQ and official references
1. How do we see a book, a lamp or the Moon?
The central idea is simple but often misunderstood: we can see an object when light travels from the object into our eyes. Some objects give out their own light. Others are visible because they reflect light from a source. The light that reaches our eyes allows us to recognise the object.
A switched-on lamp gives out light. A book normally does not. In a well-lit classroom, light from the Sun or an electric lamp strikes the book and some is reflected towards the observer. The book is visible. When the room becomes completely dark and no light reaches the book or the eyes, the book cannot be seen in the same way.
The Moon is a classic comparison. It looks bright in the night sky but is visible mainly because it reflects light from the Sun. That does not make it a source of visible light like the Sun for the purposes of an ordinary Primary Science question. Distinguish producing light from reflecting it.
A mirror makes this difference memorable. The mirror does not usually create light; it reflects light. We can see our reflection when light travels from a source to us, is reflected from us to the mirror and back towards our eyes. For Primary Science, explaining that light is reflected into the eyes is enough. Detailed reflection-angle calculations belong beyond the named P4 Light requirement.
Pupils sometimes say that eyes emit rays that illuminate objects. That is wrong for ordinary human vision. Eyes receive light; they do not normally send visible illumination across the room. A student can check the explanation by imagining a book in a completely dark room. Staring harder at the book does not light it up.
It is also possible for an object to be seen even though the source of illumination is not in the picture. If a diagram shows light rays arriving from the side and reaching the object, the relevant explanation still follows: light is reflected from the object into an observer’s eyes. A diagram need not include the entire Sun or ceiling lamp to show that mechanism.
A good exam response is short: “The book can be seen because light from the lamp is reflected by the book into the pupil’s eyes.” That names source, reflection and observer without introducing irrelevant anatomical detail.
| Situation | Does the object give out its own light? | How can it be seen? |
|---|---|---|
| Switched-on torch | Yes | It emits light that reaches an observer |
| Unlit textbook | No | It reflects light from another source |
| Moon | Not a source of its own visible illumination in the classroom model | It reflects sunlight |
| Mirror | No, not ordinarily | It reflects light from other objects or sources |
| Switched-off electric lamp | No | Its surface can reflect other light |
| Illuminated reflective road sign | No, in the stated situation | It reflects incident light from a vehicle or other source |
Why reflection does not mean ‘bouncing perfectly like a ball’
Different surfaces reflect light differently. A smooth mirror produces a clear image under suitable conditions. Paper reflects light in many directions, so it is visible from many positions without forming a sharp mirror image. An object that scatters light is still reflecting some of it.
Avoid saying that an object is invisible simply because it is not shiny. A matte black surface may reflect less light than a white surface under comparable conditions, but if sufficient light reaches the observer’s eyes, it can still be seen. Brightness depends on incident light, surface properties and viewing conditions.
The MOE Primary Light syllabus explicitly says that the law of reflection is not required. Pupils need to know that light can be reflected into the eyes, but they should not spend revision time memorising angle-of-incidence equal to angle-of-reflection diagrams unless their school uses them as enrichment.
2. Why a shadow forms when light travels in straight lines
In the basic school model, light travels in straight lines through a uniform medium. When an object lies between a light source and a screen, the object may block some or all of the light that would otherwise reach part of the screen. The darker region is a shadow.
The shadow is not a substance being produced by the object. It is a region where less light reaches. If a book is placed in front of a torch, parts of the wall behind the book may receive no direct light from that source. Remove the book and the wall is illuminated more evenly.
A student’s drawing should make the geometry clear: light source first, obstructing object next, screen behind. Drawing the arrow from the screen towards the torch reverses the direction of light in a source-to-screen experiment. If the object is moved to one side, its shadow can shift accordingly, because the blocked paths change.
Under a small point-like source, shadow boundaries can be approximated by drawing straight lines from the source past the edges of the object. A larger light source can produce regions of full and partial shadow. Primary pupils do not need advanced optical ray terminology to explain why a shadow may be lighter at its edges or why a material that passes some light produces a less dark region.
The number and arrangement of sources also matter. Two torches shining on one object can create two shadows in different positions. If one torch is turned off, the pattern changes. This is a useful way to test whether a pupil understands source position rather than memorising one silhouette.
The object’s shape matters as well. A circular disc and a rectangular card placed in similar arrangements may cast differently shaped shadows. Rotating a rectangular card can alter the shape of its shadow even when the card’s physical size remains the same. Students should not assume that a shadow always displays the full front-facing outline of a three-dimensional object.
Ordinary outdoor shadows depend on the Sun’s position, the object and the surface receiving the shadow. Shadow direction changes as the apparent position of the Sun changes over the day. But a claim such as “all shadows are shortest exactly at 12:00 noon” is not reliable for every latitude, season, time zone or location. Use the diagram and the stated light position.
One simple model and three possible mistakes
- Locate the luminous source: torch, lamp or Sun.
- Identify the object between source and receiving surface.
- Find the region where direct light is blocked.
- Check that the shadow lies on the opposite side from the source in the simple straight-line setup.
- Describe the shape and size based on the actual geometry rather than assuming the shadow is identical to the object.
- When two sources are present, trace each source separately before counting dark regions.
3. Torch–object–screen questions: understand all three distances
The familiar diagram contains a source, an object and a screen. The key variables are the source–object distance and the object–screen distance. Changing either can alter shadow size and position. A student who learns “closer means bigger” without specifying closer to what is likely to be misled.
Imagine the torch and screen are fixed, and a small opaque card moves along the line between them. When the card is nearer the torch, the light rays passing the card’s edges spread across a larger region of the screen. The shadow is generally larger. As the card moves nearer the screen, the shadow usually becomes smaller and approaches the card’s apparent outline.
Another experiment holds the object in place and moves the screen further behind it. The shadow may enlarge because the rays defining its boundary spread farther before reaching the screen. If the screen moves closer to the object, the shadow may shrink.
These relationships assume a simple source and comparable alignment. A broad light source or a complex object can change the appearance of the shadow edges. Read the figure instead of treating a rule memorised for a point torch as universal.
A strong explanation says: “With the torch and screen unchanged, moving the card nearer the torch increases the size of its shadow because it blocks a larger spread of light reaching the screen.” The answer does not need a formula. It needs to identify which distance changed and why that matters.
Students can make their own paper-based experiments using printed rays and movable card drawings. Physical practice with a safe battery torch and a paper screen can also be useful with adult supervision. Never shine a bright torch, laser pointer or sunlight into anyone’s eyes, and never use a magnifying glass to focus sunlight onto people or flammable objects.
| Change in simple setup | What stays fixed | Typical shadow result |
|---|---|---|
| Object moves nearer small lamp | Lamp and screen | Larger shadow |
| Object moves nearer screen | Lamp and screen | Smaller shadow |
| Screen moves farther behind object | Lamp and object | Larger shadow |
| Screen moves towards object | Lamp and object | Smaller shadow |
| Object moves to the left | Lamp and screen | Shadow position changes; draw paths to determine where |
| Object rotates | Lamp, screen and object position | Shadow shape may change |
4. Shadow shape, size and position are separate features
A shadow can be large yet have the same general shape as before. It can shift sideways while remaining almost the same size. It can change shape because the object rotates, not because the object grows or shrinks. These are three different observations.
When a question asks which variable affects the size of the shadow, answer with a relevant distance or size change. When it asks why the shadow moved, examine which part of the setup shifted. A learner who answers “the shadow becomes bigger” to every diagram change has not read the actual question.
In a diagram with a flat screen and rectangular card, an angled card may cast a narrower apparent shadow. Some parts of a three-dimensional object may be hidden behind others from the source’s perspective, changing the silhouette. A printed image can be misleading if pupils infer physical thickness or orientation that the labels do not establish.
Always distinguish an observation from a cause. “The shadow was 12 cm tall” is a measurement. “The shadow became taller when the card was moved closer to the lamp while the lamp and screen were fixed” is a recorded relationship. “The larger shadow results because the card blocks a broader spread of light reaching the screen” is the proposed mechanism.
Exam diagrams often test whether a pupil can interpret an apparatus from more than one view. The top view may show left–right shadow positions, while the side view may show height. Read labels such as ‘side view’, ‘front view’ and ‘screen’ before drawing your conclusion.
One extra test is to ask what happens when the object is removed. If no object blocks the source’s light, the corresponding shadow disappears. This establishes that the dark region depends on blocking, not on a coloured stain or the screen itself.
A shadow answer that earns its place
Question: A card is moved from Position A to Position B, closer to a small torch. The screen is unchanged. Compare the shadow sizes.
Response: The shadow at Position B is larger than at A. The card is nearer the torch, so it blocks light over a larger area of the fixed screen.
Avoid: “It is bigger because it is near” without naming what is nearer and explaining which region receives less light.
5. Materials and the passage of light
The MOE 2023 syllabus deliberately focuses on what materials do rather than requiring every child to reproduce specialist labels. In Primary 3, pupils compare transparency—the passage of most, some or no light—and relate it to useful material choices. In Primary 4, they examine shadows when light is completely or partially blocked. The specific words “transparent”, “translucent” and “opaque” are not compulsory syllabus vocabulary for these learning outcomes.
These words can still be useful as ordinary language: clear glass lets most visible light through; frosted glass allows some light through but scatters it; wood blocks visible light in the ordinary example. But if the child knows the three names and cannot explain how the screen looks, the important scientific skill is missing.
Some materials transmit light and still make the view blurry because light is scattered. Another material may let most light through and produce little shadow. A thick card may block light and produce a dark region. Use the observation in the supplied question. Real materials have varying thickness, surface texture and colour, so a universal claim based only on the name “plastic” is risky.
A student might be asked why glass is useful for a window. A suitable answer is that it allows most visible light to pass through and allows people to see through it, subject to its type. Why use a dark, light-blocking curtain? It reduces light entering the room. A child should link property to use, not merely recite a category.
This topic connects to material selection. A raincoat must resist water absorption; a window must transmit light; a book cover may need strength and flexibility. The same material can be described using several properties, but the property relevant to the device’s function is the one to name.
For shadow explanations, avoid assuming that a material that passes some light must produce the same darkness as a thick opaque card. The extent of blocking matters. It is the quantity of light reaching the receiving surface that determines the appearance of the shadow in the described conditions.
| Material example | Light behaviour in ordinary classroom conditions | Use or consequence |
|---|---|---|
| Clear glass | Allows most visible light through | Windows or clear viewing surfaces |
| Frosted glass | Allows some light through while scattering it | Privacy screening with daylight |
| Thick cardboard | Blocks most or all incident visible light | Makes a darker shadow |
| Thin tracing paper | Allows some light through | Softens and scatters light |
| Wooden board | Blocks visible light | Can create a dark shadow when placed before a screen |
| Clear plastic sheet | Often allows much visible light through, depending on the product | Can protect a display while retaining visibility |
6. How to read shadow experiments, tables and graphs
A source–object–screen experiment needs clear variable control. Suppose a pupil investigates how moving a card affects shadow size. Keep the lamp, screen and card type comparable and change the chosen position. Then measure the shadow’s width or height in the same way each time.
If both the lamp and card move, the data cannot isolate the effect of card position alone. If one card is twice as wide as another, the shadow comparison involves more than distance. A strong answer to “How could the pupil improve the experiment?” names the confounding factor and states exactly how to control it.
Read the table headings before the values. Shadow height, shadow width and shadow area are different measurements. A taller shadow is not necessarily a wider shadow. A diagram may use centimetres, while a graph shows differences in millimetres. Use the stated scale and units.
If a table shows greater shadow width as a card moves closer to the lamp with the screen fixed, the pupil can describe that relationship over the investigated range. Do not claim the shadow will continue growing without limit when the object is moved beyond the physical setup. A scientific conclusion must stay within the conditions tested or state assumptions for extrapolation.
Some questions ask for the independent variable; others ask for the dependent or measured variable. The independent variable is the factor deliberately changed. The measured result is the shadow dimension or position. Controlled variables may include card size, source position, screen position and alignment. Students should identify which are actually relevant rather than recite “keep everything else the same”.
| Card position from lamp | Shadow height (cm) | What the data show |
|---|---|---|
| 10 cm | 18 | Largest recorded shadow |
| 15 cm | 12 | Intermediate recorded shadow |
| 20 cm | 9 | Smallest recorded shadow |
In this original table, the height of the shadow decreases as the card’s distance from the fixed lamp increases over the measured positions. The data are consistent with the simple geometry, assuming the screen stayed fixed. That is a valid description.
It would be incorrect to say the card itself shrank. The actual card remained the same size. It would also be incorrect to claim that the values reveal exactly how much light energy the torch produced; shadow dimensions do not directly measure emitted energy.
A useful extension asks how the experiment could compare shadow shape rather than size. The pupil might rotate the same card while holding the light source, screen and relative positions constant, recording the shadow outline at each orientation.
7. Twenty original light and shadow questions with model answers
1. How can a book be seen?
Question: A book is visible in a lit room. Why?
Reasoned answer: Light from a source is reflected by the book into the observer’s eyes.
Exam trap: Do not say the eye sends out light.
2. Sun or Moon?
Question: Which is the direct visible light source in the familiar Sun–Moon system?
Reasoned answer: The Sun; the Moon is normally seen by reflected sunlight.
Exam trap: Brightness does not necessarily imply producing light.
3. Switched-off torch
Question: Can an unlit torch still be seen in daylight?
Reasoned answer: Yes, because it can reflect sunlight into our eyes.
Exam trap: Being visible does not mean the torch is emitting light.
4. Straight-line travel
Question: Why does a solid card form a shadow behind it?
Reasoned answer: It blocks the straight-line travel of some or all light to the receiving surface.
Exam trap: A shadow is a region receiving less light, not a substance.
5. Shadow side
Question: A lamp is to the left of a ball. Which side receives the ball’s simple shadow on a screen?
Reasoned answer: On a screen positioned behind the ball, generally to the right, away from the lamp.
Exam trap: Use the actual positions shown.
6. Card nearer torch
Question: The screen and lamp stay fixed. The card moves closer to the lamp. What happens to the shadow?
Reasoned answer: It generally becomes larger for a small source.
Exam trap: Name the source–object distance.
7. Card nearer screen
Question: The lamp and screen stay fixed. The card approaches the screen. What happens?
Reasoned answer: The shadow generally becomes smaller.
Exam trap: Do not memorise ‘closer = larger’ without specifying to what.
8. Screen moves back
Question: The object and point source stay fixed, and the screen is moved farther away. What changes?
Reasoned answer: The shadow generally grows larger.
Exam trap: The card itself has not changed.
9. Shape versus size
Question: A rectangular card turns sideways without changing distance. Which shadow feature may change?
Reasoned answer: The shadow’s shape and width may change because orientation changes.
Exam trap: Do not assume the card’s actual dimensions have changed.
10. Two lights
Question: Two lamps illuminate a card from different positions. Can two shadows appear?
Reasoned answer: Yes; each source can create a distinct shadow pattern.
Exam trap: Trace each lamp separately.
11. Light-blocking material
Question: A thick wooden card is placed before a torch. Will most light pass through it?
Reasoned answer: No in the ordinary classroom setup; it blocks visible light and makes a dark shadow.
Exam trap: Technical labels are not the main syllabus requirement.
12. Clear glass
Question: Why does a clear window help a room receive daylight?
Reasoned answer: It allows most visible light to pass through.
Exam trap: Glass type and condition matter.
13. Frosted panel
Question: Why might a frosted panel give privacy while allowing some daylight?
Reasoned answer: It transmits and scatters light, so images are less clear.
Exam trap: Some light transmitted does not mean no light is blocked.
14. Reflected light
Question: Why can a mirror show an image of a nearby object?
Reasoned answer: Light reflected from the object reaches the mirror and is reflected into the observer’s eyes.
Exam trap: No law-of-reflection calculation is needed.
15. Unfair test
Question: A pupil changes both the card width and distance. Can distance alone explain a larger shadow?
Reasoned answer: Not reliably; card width also changed.
Exam trap: Control the size of the card.
16. Changed variable
Question: A pupil moves a card through three positions while measuring shadow height. What is deliberately changed?
Reasoned answer: The card’s position, or its distance from the light source as specified.
Exam trap: Do not confuse it with measured shadow height.
17. Measured variable
Question: In the same test, what is the outcome measured?
Reasoned answer: The shadow’s height on the screen.
Exam trap: Use the stated unit if provided.
18. Data trend
Question: Shadow height is 18 cm at 10 cm, 12 cm at 15 cm, and 9 cm at 20 cm from a fixed lamp. Describe the trend.
Reasoned answer: The recorded shadow height decreases as the object–lamp distance increases.
Exam trap: This describes the tested range, not every possible position.
19. Outdoor shadow
Question: A shadow changes direction during the day. What changes in the basic model?
Reasoned answer: The apparent position of the Sun relative to the object and ground changes.
Exam trap: Do not claim every place has the shortest shadow at clock noon.
20. No light
Question: Why is an unlit book difficult to see in a completely dark room?
Reasoned answer: Without light reaching and reflecting from the book into the eyes, it cannot be seen normally.
Exam trap: Staring harder does not create light.
8. Five errors that return in PSLE light questions
1. Source versus reflector
A visible object may reflect light instead of emitting it; an ordinary book and the Moon are key contrasts.
2. Eye sends light outward
Light reaches our eyes from sources directly or after reflection from other objects.
3. ‘Closer’ has no reference point
State closer to the torch or closer to the screen; the predictions can differ.
4. Shadow dimensions equal object dimensions
The geometry and orientation can enlarge, shrink or reshape a shadow without changing the object itself.
5. Material labels are the answer
The official syllabus focuses on whether most, some or no light passes; the named technical terms are not required.
9. A four-week P6 revision cycle for light and shadows
| Week | Main task | Independent success |
|---|---|---|
| 1 | Sources, reflected light and straight-line travel | Explain why a book, Moon and switched-off lamp are visible |
| 2 | Source–object–screen diagrams and shadow formation | Predict size and position changes from different layouts |
| 3 | Material transmission, shadow shape, fair tests and short data tables | Explain blocked light and read unfamiliar results |
| 4 | Mixed MCQ and Booklet B-style worked questions with delayed retests | Give precise answers without an identical model drawing |
A useful revision session lasts about 25–35 minutes for many pupils, but adjust to the child’s attention, other subjects and needs. Begin with three quick retrieval prompts, then an unfamiliar diagram, then an explanation in the child’s words. Review the most important error rather than completing a large pile of nearly identical worksheets.
In the first week, a parent can ask a child to identify five objects at home and distinguish those that emit their own light from those usually visible by reflection. The child should explain rather than simply label. If the light is off, an ordinary object can still be seen through daylight entering the room. The real condition is whether light reaches the object and the eyes.
In the second week, use three printed torch–screen diagrams. Keep the source and screen fixed in each set; move the card and draw the predicted shadow before looking at the answer. Then reverse the change. A pupil who understands the geometry should be able to explain both directions coherently.
In the third week, combine the idea with material selection: why a clear cover helps seeing a display, why a dark card blocks light, and why frosted glass admits light while obscuring details. The technical terminology can be introduced as enrichment, but the property-to-use explanation comes first.
In the fourth week, mix light with an apparently unrelated scientific skill. A table of shadow heights requires graph reading and variable control. An animal shelter question may involve shade and environmental conditions. A home-energy example may involve an electric light and the distinction between source, electricity and energy conversion. The connections matter because real PSLE questions can combine concepts.
When a child makes a mistake, record whether it was a wrong light-source identification, reversed ray direction, confused distance, overlooked material or misread table. Retest the same reasoning later in a new setting. “I memorised the sentence about closer shadows” is not proof of mastery if the child cannot identify the distance that changed.
No child needs to stare directly at a bright source, laser beam or the Sun to investigate light. Use safe diagrams and low-intensity household lamps or torches under adult supervision. Experiments that focus sunlight with lenses or mirrors are unsafe and unnecessary for this lesson.
The long-term value of learning about light is not limited to a Science grade. Reflection, visibility and light-blocking properties help explain road signs, room design, window materials, safe lighting and sensible energy use. A clear description of source, path and obstacle is also an early introduction to systems thinking.
10. Frequently asked questions
Is light still in PSLE Science although it is taught in Primary 4?
Yes. Standard PSLE Science expects pupils to retain and apply relevant Primary 3–6 content, including light in the Energy theme.
Does the 2023 MOE syllabus require the law of reflection?
No. The Primary 4 Light learning outcome explicitly says the law of reflection is not required.
Do children have to memorise transparent, translucent and opaque?
Those specific terms are not required by the MOE 2023 Primary 3 material-transparency and Primary 4 light outcomes. Pupils should understand whether most, some or no light passes through.
Why can we see the Moon?
It is visible mainly because it reflects sunlight towards observers.
Why is a shadow formed?
Light travels in straight lines, and an object blocks some or all of the light reaching part of a receiving surface.
Does moving the object closer always make the shadow larger?
Not without saying closer to what. In a fixed small-torch-and-screen setup, nearer the torch generally means larger, while nearer the screen means smaller.
Can a shadow change shape without the object changing size?
Yes. Rotation and the relative geometry of object, source and screen can change its outline.
Can a material that allows some light through create a shadow?
Yes. If it blocks some light, the receiving region can be less brightly lit.
Does a light source need to be inside the diagram for an object to be visible?
Not necessarily. The diagram may assume illumination from outside its frame; rely on the given conditions.
Can any tuition site predict the PSLE Science light question for 2027?
No. The official syllabus identifies learnable concepts, but not future examination questions.
Official sources and further reading
- MOE 2023 Science Syllabus, May 2024 update, pages 39–40 and 75
- SEAB official PSLE Science paper format from 2026
- 12-week PSLE Science 2027 timetable
- Fair tests, measured variables, tables and graphs
- P4 Heat and Light: additional diagram questions
- Electric circuits and energy conversion
- eduKate Singapore parent–student consultation
Reviewed 12 November 2026 against MOE’s 2023 syllabus (updated May 2024) and the latest verified SEAB paper-format page. All questions are original teaching examples, not examination leaks or predictions. eduKateSG is independent of MOE and SEAB.