Class 7 Science Chapter 11 – LIGHT Exam-Ready Running Notes

 Class 7 Science

Chapter 11 – LIGHT

Running notes

1. Important Terms (Very Important ⭐)

Object: The thing placed in front of a mirror or lens.

Image: The picture formed by a mirror or lens.

Real Image:

Can be obtained on a screen

                             Always inverted

        Example:

Concave mirror

Convex lens

Virtual Image:

Cannot be obtained on a screen

Always erect

                Example:

Plane mirror

Convex mirror

Concave lens

2. Reflection of Light

Reflection is the bouncing back of light from a shiny surface.

Any polished or shiny surface can act like a mirror.

Common mirrors:

Plane mirror

Concave mirror

Convex mirror

3. Plane Mirror – Image Characteristics ⭐⭐

Image formed by a plane mirror is:

Virtual

Erect

Same size as the object

Formed behind the mirror

Image distance = Object distance

Shows lateral inversion (left ↔ right)

Example: Dressing mirror

4. Lateral Inversion

Left side of the object appears as right side in the image.

Reason why “AMBULANCE” is written reversed.

5. Spherical Mirrors

(a) Concave Mirror (Reflecting surface curves inward)

Image formed:

Can be real or virtual

Can be larger or smaller

Uses:

Headlights of vehicles

Dentist mirror

Solar cooker

(b) Convex Mirror (Reflecting surface bulges outward)

Image formed:

Always virtual

                             Always erect

                          Always smaller

Uses:

Side-view mirrors in vehicles

Security mirrors

6. Which Mirror Forms Real Image? ⭐

Ans:  Concave mirror

7. Lenses

(a) Convex Lens (Thick in middle)

Also called converging lens

Can form:

Real image

Virtual image (when object is close)

Uses:

Magnifying glass

Camera

Microscope

(b) Concave Lens (Thin in middle)

Also called diverging lens

Always forms:

Virtual

Erect

Smaller image

Uses:

Spectacles for short-sightedness

8. Differences Between Convex and Concave Lens ⭐⭐

Convex Lens                                     Concave Lens

Thick at centre                                     Thin at centre

Can form real or virtual image                 Always forms virtual image

Used as magnifying glass                         Used in spectacles

 

9. Which Lens Always Forms Virtual Image? ⭐

Ans: Concave lens

        10. Comparison Table – Mirrors/ lens & Images (Quick Revision) 

Mirror / Lens	Type of Image Formed	Nature of Image	Size of Image	Position of Image	Important Notes / Uses
Plane Mirror	Virtual	Erect	Same size as object	Behind the mirror	Image distance = object distance; shows lateral inversion
Concave Mirror	Real or Virtual	Real image → Inverted Virtual image → Erect	Can be larger, smaller, or same	Real image → In front of mirror Virtual image → Behind mirror	Used in headlights, dentist mirrors; real image forms when object is far, virtual when object is very close
Convex Mirror	Always Virtual	Erect	Always smaller	Behind the mirror	Gives wide field of view; used as side-view mirrors in vehicles
Convex Lens	Real or Virtual	Real image → Inverted Virtual image → Erect	Can be larger or smaller	Real image → Opposite side of object Virtual image → Same side	Used as magnifying glass; real image forms when object is far
Concave Lens	Always Virtual	Erect	Always smaller	Same side of object	Used in spectacles for short-sightedness

11. Important Numericals (Concept Based)

Plane Mirror Rule ⭐

Distance of object = Distance of image

If object moves x m, image also moves x m

        Total distance change = 2x

12. Sunlight and Colours

Sunlight (white light) is made up of 7 colours:

VIBGYOR

(Violet, Indigo, Blue, Green, Yellow, Orange, Red)

A prism splits white light into 7 colours.

Rainbow is formed due to:

Reflection

Refraction

Dispersion of sunlight