Class 7 Science Chapter 11: Light - Shadows and Reflections

(From NCERT Curiosity Textbook, Reprint 2026-27 – Easy Notes in Simple Words)

This chapter explains how light helps us see, why shadows form, and how mirrors make reflections. Everything uses simple language for easy remembering. Key points repeat like a story.

11.1 Sources of Light (What gives light?)

• Luminous objects: Give their own light. Examples: Sun, stars, fireflies, lightning, candle flame, electric bulb, torch.
• Non-luminous objects: Do not give own light. They look bright only when light falls on them. Example: Moon (reflects Sun's light), book, table, chair.

Remember tip: Luminous = Like a lamp (own light). Non-luminous = Like Moon (borrowed light).

Natural sources: Sun (main), stars, fireflies, lightning. Artificial (man-made): Fire (old), oil lamps, candles, electric bulbs, LEDs.

Fun fact: LED bulbs save electricity, last longer, and are good for environment. Government promotes them. Dispose properly, don't throw in dustbin.

Graphic idea (Imagine this diagram): Sun and stars glowing → Firefly flashing → Bulb and torch shining. Moon shown with arrow from Sun saying "reflects light".

11.2 Does Light Travel in a Straight Line?

Yes! Light travels in straight lines. This is called rectilinear propagation.

Activity 11.1 (Matchbox holes): Make holes in 3 matchboxes at same height. Line them straight. Torch light passes and makes spot on screen. If you move one box, light stops. Shows straight path.

Activity 11.2 (Pipe): See candle flame through straight pipe → Yes. Bend pipe → No. Again proves straight line.

Remember: Light goes like an arrow → straight, not curved.

11.3 Light through Different Materials

Materials classified by how much light passes:

Type	Light Passes	Examples	See Through?
Transparent	Fully/completely	Glass, clear water, air	Yes, clearly
Translucent	Partially/some	Tracing paper, frosted glass, thin cloth	Yes, but blurry
Opaque	Not at all	Cardboard, wood, metal, thick book	No

Activity 11.3: Put objects in front of torch. Predict then check if light spot on wall/screen remains.

Laser tip (for fun): Laser beam in milky water shows straight path clearly.

Remember rhyme: Transparent = Full view, Translucent = Fuzzy clue, Opaque = No light through!

Graphic: Torch → Glass (full light), Butter paper (dim light), Wood (shadow). Table like above.

11.4 Shadow Formation

• When opaque object blocks straight light → dark patch on screen/wall = Shadow.
• Shadow needs: Light source + Opaque object + Screen (wall/ground).
• Shadow is dark because light cannot reach there.
• Size changes with distance.

Why shadow? Light stops at opaque object. Area behind it stays dark.

Pinhole Camera (Simple science toy): Box with small hole on one side, tracing paper on other. Image forms upside down on paper because light travels straight from object through tiny hole.

Activity idea: Make pinhole camera with shoebox. See inverted image of candle or tree.

Remember: Bigger distance from light → bigger shadow. Closer to screen → smaller shadow.

11.5 Reflection of Light

• When light bounces back from surface = Reflection.
• Smooth shiny surfaces (mirrors) give clear reflection.
• Rough surfaces scatter light → no clear image.

Plane Mirror (flat mirror):

• Image is virtual (not real, cannot catch on screen).
• Same size as object.
• Image is behind mirror, same distance as object is in front.
• Lateral inversion: Left and right swap. (Your right hand looks like left in mirror).

Periscope: Uses two plane mirrors at 45° angle. Helps see over walls or around corners (used in submarines). Light reflects twice.

Activity: Stand in front of mirror. Raise right hand → mirror image raises left. Walk closer → image closer.

Remember table:

• Image in plane mirror: Erect (straight), virtual, same size, laterally inverted.

Key Points to Remember (A-Z Quick Revision)

• Angle of incidence = Angle of reflection (law, for higher classes).
• Bright source makes sharp shadows.
• Candle flame through straight pipe only.
• Dark shadow from opaque.
• Electric light common now.
• Fireflies are luminous.
• Glass is transparent.
• Hole in pinhole camera makes inverted image.
• Image in mirror is virtual.
• Lateral inversion in mirror.
• Moon is non-luminous.
• Opaque blocks all light.
• Periscope for seeing around.
• Rectilinear = straight line.
• Shadow needs 3 things.
• Translucent = partial light.
• Upside down in pinhole.
• Virtual image cannot be caught.
• Wall as screen for shadow.

Real Life Uses:

• Mirrors in bathroom, vehicles.
• Shadows tell time (sundial).
• Periscope in ships/submarines.
• Pinhole for safe solar eclipse viewing (never look direct at Sun).

Questions type for exam:

1. Why shadows form?
2. Difference between transparent/translucent/opaque.
3. What is lateral inversion?
4. How does periscope work?
5. Draw ray diagram for straight line propagation.

Study with drawings daily. Make your own shadow puppets with hands in torch light for fun revision! These notes cover full chapter in easy words. Revise tables and activities for best marks.