🔷 1. What is Light?
Light is a form of energy that helps us to see things.
When light falls on an object and reaches our eyes, we can see that object.
Without light, everything looks dark.
Examples:
- We see everything clearly in daylight.
- We use bulbs, torches, or candles to see at night.
🔷 2. Sources of Light
| Type of source | Meaning | Examples |
| Natural sources | Found in nature and give out their own light | Sun, stars, lightning, firefly |
| Man-made sources | Made by humans; need fuel or electricity to glow | Candle, torch, bulb, tube-light |
🔷 3. Importance of Light
- Helps us see objects.
- Enables plants to make food by photosynthesis.
- Keeps Earth warm.
- Helps us in daily activities like reading, cooking, and walking.
🔷 4. How We See Objects
Light from a source falls on an object and bounces (reflects) into our eyes.
That’s why we can see the object.
Example: You can see a tree because sunlight reflects from the tree into your eyes.
🔷 5. Types of Objects (Based on Light Passing Ability)
| Type of Object | What it means | Examples |
| Transparent | Lets light pass completely; we can see through it | Glass, clean water, air |
| Translucent | Lets only part of the light pass; we see blurred images | Butter paper, frosted glass, thin cloth |
| Opaque | Does not let light pass; we can’t see through it | Wood, wall, book, metal plate |
🔷 6. What is a Shadow?
A shadow is a dark shape formed when an opaque object blocks light.
Light travels in straight lines, so an opaque object stops it and a shadow forms on the opposite side.
Example:
When you stand in sunlight, your body blocks the light, forming your shadow on the ground.
🔷 7. Conditions Needed to Form a Shadow
- A source of light (Sun, bulb, torch)
- An opaque object (your body, a ball, a tree)
- A surface for the shadow to fall on (ground, wall, floor)
🔷 8. Properties of Shadows
- Always black or dark in colour.
- Change size according to distance of the light source:
- Light close → large shadow
- Light far → small shadow
- Light close → large shadow
- Change position with direction of light.
- Show shape of the object but not colour or details.
🔷 9. Shadows During the Day
| Time | Sun’s position | Size & direction of shadow |
| Morning | Low in east | Long shadow towards west |
| Noon | Overhead | Very short shadow |
| Evening | Low in west | Long shadow towards east |
🔷 10. Light Travels in a Straight Line
This property is called rectilinear propagation of light.
That is why shadows have definite shapes and are formed in straight lines.
Activity:
Make three holes in a straight line on three cardboards.
Hold them in front of a candle flame. You can see the light through all holes.
If one board is moved aside, light is blocked — proving light travels straight.
🔷 11. Formation of Day and Night
- The Earth rotates (spins) on its axis once in 24 hours.
- The part facing the Sun has day.
- The part away from the Sun has night.
This constant rotation causes regular day and night.
🔷 12. Motions of the Earth
| Motion | Time taken | Result |
| Rotation | 24 hours | Causes day and night |
| Revolution | 365 days | Causes change of seasons |
🔷 13. Eclipses (Simple Explanation)
| Type | Description | Example |
| Solar Eclipse | The Moon comes between the Sun and Earth, blocking sunlight. | Sun 🌞 → Moon 🌑 → Earth 🌍 |
| Lunar Eclipse | The Earth comes between the Sun and Moon, and Earth’s shadow falls on the Moon. | Sun 🌞 → Earth 🌍 → Moon 🌑 |
🔷 14. Difference Between Light and Shadow
| Light | Shadow |
| Helps us to see objects | Formed when light is blocked |
| Can be bright or dim | Always dark |
| Shows colour and shape | Shows only shape |
| Travels in straight line | Formed opposite to light source |
🔷 15. Simple Experiments
(a) Shadow Size Experiment
- Shine a torch on a toy kept near a wall.
- Move torch closer → shadow becomes bigger.
- Move torch away → shadow becomes smaller.
(b) Transparent Test
Hold glass, paper, and wood in front of a torch:
- Glass → light passes fully
- Paper → light passes partly
- Wood → no light passes
🔷 16. Daily-Life Examples
- We see our shadow while walking in sunlight.
- Tree shadows move and change length during the day.
- Street-light shadows at night show the same rule.
- Bathroom glass (frosted) is translucent — allows light but not clear view.
🔷 17. Keywords and Meanings
| Word | Meaning |
| Light | Energy that helps us see |
| Transparent | Lets all light pass |
| Translucent | Lets some light pass |
| Opaque | Blocks light completely |
| Shadow | Dark image formed when light is blocked |
| Rotation | Spinning of Earth on its axis |
| Revolution | Earth moving around Sun |
| Eclipse | Shadow formed in space during Sun-Moon-Earth alignment |
🔷 18. Question–Answers
Q1. What is light?
➡ Light is a form of energy that helps us to see things.
Q2. Name two natural and two artificial sources of light.
➡ Natural: Sun, stars Artificial: Bulb, candle.
Q3. Why can’t we see in the dark?
➡ Because no light reflects from objects to our eyes.
Q4. Define a shadow.
➡ A shadow is a dark shape formed when an opaque object blocks light.
Q5. List the three conditions needed to form a shadow.
➡ Light source, opaque object, and a surface.
Q6. How does the size of a shadow change?
➡ Closer light → larger shadow; farther light → smaller shadow.
Q7. What causes day and night?
➡ The rotation of the Earth on its axis.
Q8. What is the difference between solar and lunar eclipse?
➡ Solar: Moon blocks Sun’s light. Lunar: Earth’s shadow covers Moon.
🔷 19. True or False
- Shadows are always coloured. → ❌ False
- Light can travel through opaque objects. → ❌ False
- The Sun is a natural source of light. → ✅ True
- We can see things only when light reaches our eyes. → ✅ True
🔷 20. Fill in the Blanks
- Light helps us to _______ objects. (see)
- Objects that do not allow light to pass are called _______. (opaque)
- The Earth rotates on its _______. (axis)
- A shadow is always _______ in colour. (black/dark)
🔷 21. Fun Facts
- The Moon doesn’t have its own light; it reflects sunlight.
- Your shadow disappears when you stand directly under the noon sun.
- The speed of light is about 3 lakh km per second!
✅ In short:
Light helps us see → Opaque object blocks light → Shadow forms → Earth’s rotation causes day & night → Eclipses are big-scale shadows in space.