This MCQ module is based on: Light — Sources, Transparent Objects and Shadows
TOPIC 39 OF 46
Light — Sources, Transparent Objects and Shadows
🎓 Class 7
Science
CBSE
Theory
Ch 11 — Light: Shadows and Reflections
⏱ ~14 min
🌐 Language: [gtranslate]
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Fireflies on a Village Evening
One warm July night, Arjun was sitting with his grandmother on the verandah of their home in a village near Chandrapur. The sky was moonless and very dark. Suddenly, dozens of tiny yellow-green sparks floated up from the mango grove — fireflies! Arjun's grandmother smiled, "Look at these little lamps! They are their own light." Arjun wondered: the Sun, a candle, a tube-light, a torch, even these fireflies — they all give light. But what about the Moon? It shines at night too. Is the Moon also making its own light?
Think first: You can see your own shoe only when there is light in the room. If a room is pitch dark, you see nothing even though the shoe is right there. This tells us something important — we do not see objects directly; we see them only when light from them reaches our eyes. So where does that light come from for different objects around us?
11.1 Sources of Light — Natural and Artificial
A source of light is any object that produces light by itself. Sources are broadly of two kinds:
| Type | Meaning | Examples |
|---|---|---|
| Natural | Occur in nature without being made by humans | Sun, stars, fireflies, some deep-sea fish, lightning |
| Artificial | Made and switched on by humans | Candle, oil lamp, tube-light, LED bulb, torch, phone screen |
11.2 Luminous and Non-luminous Objects
Objects that produce their own light are called luminous objects. Objects that do not make their own light — but we still see them because light from a luminous object bounces off them — are called non-luminous objects.
The Tricky Case of the Moon
The Moon looks bright on a clear night, so we easily assume it is a source of light. It is not! The Moon has no fire, no filament, no glowing chemical. It simply reflects sunlight that falls on it. That is why we see different shapes of the Moon (phases) — only the part lit up by the Sun is visible to us.
Rule: The Sun is luminous. The Moon is non-luminous — it shines only with borrowed light.
11.3 How Materials Behave with Light — Transparent, Translucent, Opaque
Hold three different things in front of a torch: a clear glass tumbler, a sheet of butter paper, and a wooden ruler. Light behaves very differently with each one.
| Material | What happens to light | Can you see through? | Examples |
|---|---|---|---|
| Transparent | Almost all light passes through | Yes, clearly | Clean glass, clear water, air |
| Translucent | Only some light passes; rest is scattered | Blurred outline only | Butter paper, frosted glass, thin cloth |
| Opaque | Light cannot pass through | No | Wood, metal, stone, your body |
11.4 Light Travels in a Straight Line
Have you ever seen a sunbeam slipping through a small gap in a window curtain on a dusty afternoon? The bright line of light is perfectly straight. Try this with a torch in a darkened room: the beam cuts a sharp straight path. Scientists call this the rectilinear propagation of light — a long phrase that simply means light moves in straight lines in any one medium.
Important: Because light travels in straight lines, it cannot bend round a corner on its own. If you stand behind a wall, you cannot see the road in front of it — the light from the road cannot curve to reach your eyes.
11.5 Shadows — When Light is Blocked
Stand in bright sunlight and look down. You will see a dark patch of your own shape on the ground — your shadow. A shadow is formed because light travels in straight lines and cannot bend around the object blocking it.
Three Conditions Needed to Make a Shadow
- A source of light (Sun, bulb, torch)
- An opaque object in the path of that light
- A screen (wall, floor, ground) behind the object to catch the shadow
Remove any one of these and there will be no shadow. Shine a torch in an empty room — no object, no shadow. Hold a ball but switch off the torch — no light, no shadow. Hold the ball and torch in empty space — no surface to show the shadow.
11.6 Why Does a Shadow Have the Shape of the Object?
A shadow copies the outline of the object because light rays are blocked along that very outline. Where rays are stopped, no light reaches the screen and the area turns dark. Where rays pass by the object, they light up the screen. The sharp boundary between the dark and bright region traces the silhouette of the object.
Interestingly, the shadow does not tell you the object's colour, texture or markings. A red ball and a blue ball of the same size cast exactly the same black shadow. That is why shadows are always black (or very dark) — the screen inside the shadow receives no light at all, so your eye reports the absence of light as black.
11.7 Why Does Shadow Size Change?
Stand far from a wall in the evening sunlight and look at your long shadow. In the afternoon, the same shadow is short. Why?
Effect of Source Distance
If the object is moved closer to the source, the shadow becomes larger because the rays that just miss the object diverge and spread wide on the screen. If the object is moved closer to the screen (farther from the source), the shadow becomes smaller and sharper.
Effect of Sun's Angle
Shadows under the Sun change size during the day because the Sun's angle changes. Early morning and late evening the Sun is low, so shadows are long. At noon the Sun is overhead — shadows are short, sometimes almost under your feet.
Activity 11.1 — Your Shadow Diary L3 Apply
You need: a sunny day, an open space, a friend, a measuring tape, chalk.
- At 8 a.m., stand with your back to the Sun in an open playground. Ask your friend to mark the tip of your shadow with chalk and measure its length.
- Repeat the measurement at 10 a.m., 12 noon and 4 p.m., always standing at the same spot.
- Record the length of the shadow and roughly the direction in which it fell each time.
Predict: At which time will your shadow be the shortest? And will the shadow always fall in the same direction?
The shadow is shortest near noon because the Sun is almost directly overhead, so rays hit you nearly vertically. At 8 a.m. and 4 p.m. the Sun is low, so the shadow is long. The direction also changes: in the morning shadows fall westward, and in the late afternoon they fall eastward — because the Sun itself moves across the sky from east to west.
Did you know? The ancient astronomer Eratosthenes used shadow lengths of a stick at Alexandria and Syene (Aswan) on the same day to estimate the Earth's circumference, more than 2,200 years ago — a beautiful use of shadow science!
Competency-Based Questions
Arjun sets up a small torch, a cardboard cut-out of a bird, and a white wall in a dark room. He lights the torch and keeps moving the bird slowly from the torch towards the wall while watching the shadow on the wall.
1. Which of the following is a luminous object? L1
(c) Candle flame — it gives out its own light. The Moon and a mirror only reflect light; a book is non-luminous.
2. Why does a book placed on the table cast a shadow under a lamp? L2
The book is opaque, so it blocks the straight-line rays of the lamp. The part of the table right behind the book receives no light and appears dark — that dark patch is the shadow.
3. Fill in the blank: A material through which some light passes but objects look blurred is called __________. L1
translucent — examples include butter paper and frosted glass.
4. As Arjun moves the bird cut-out away from the torch and closer to the wall, how does its shadow change? L3
The shadow becomes smaller and sharper. This is because the rays that pass by the edges of the bird have less distance over which to diverge before hitting the wall, so the dark patch shrinks and its outline becomes crisper.
5. True or False: A red ball will cast a red shadow on a white wall. L1
False. A shadow is simply the absence of light, so it is always dark (black). The colour of the object does not transfer to the shadow.
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R does not explain A. (C) A true, R false. (D) A false, R true.
A: The Moon is not a luminous body.
R: The Moon has no fire or filament of its own; it only reflects the sunlight falling on it.
(A) — both statements are true, and R correctly explains why the Moon is classified as non-luminous.
A: A shadow always has the same shape as the boundary of the opaque object.
R: Light travels in straight lines, so rays are blocked along the object's outline.
(A) — the shadow's shape comes directly from the straight-line travel of light; the outline of the object traces the edge of darkness on the screen.
A: We cannot see objects placed inside a completely dark room.
R: Our eyes produce light to see non-luminous objects.
(C) — A is true. R is false; our eyes do not emit light. We see non-luminous objects only because light from some source reflects off them into our eyes.
Frequently Asked Questions — Light — Sources, Transparent Objects and Shadows
What does the topic 'Light — Sources, Transparent Objects and Shadows' cover in Class 7 Science?
The topic 'Light — Sources, Transparent Objects and Shadows' is part of NCERT Class 7 Science Chapter 11 — Light: Shadows and Reflections. It covers the key ideas of light, luminous objects, transparent, translucent, opaque, shadows, umbra, penumbra, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Light — Sources, Transparent Objects and Shadows' important for Class 7 NCERT Science?
'Light — Sources, Transparent Objects and Shadows' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 11 — Light: Shadows and Reflections — introduces light and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Light — Sources, Transparent Objects and Shadows?
The key concepts in 'Light — Sources, Transparent Objects and Shadows' for Class 7 Science are: light, luminous objects, transparent, translucent, opaque, shadows, umbra, penumbra. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 11 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Light — Sources, Transparent Objects and Shadows taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Light — Sources, Transparent Objects and Shadows' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 11 — Light: Shadows and Reflections — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
What real-life examples of light can Class 7 students observe at home?
Class 7 students can observe light at home in many simple ways linked to 'Light — Sources, Transparent Objects and Shadows'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 11 — Light: Shadows and Reflections. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Light — Sources, Transparent Objects and Shadows' connect to other chapters of Class 7 Science?
'Light — Sources, Transparent Objects and Shadows' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of light appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 11 — Light: Shadows and Reflections — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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