Light

 Here are important definitions from Class 10 Science – Light (Reflection & Refraction) in simple exam-ready language 👇

📘 Important Definitions (Light Chapter)

🔹 1. Reflection of Light

Definition:

The bouncing back of light from a surface is called reflection of light.

🔹 2. Refraction of Light

Definition:

The bending of light when it passes from one medium to another is called refraction.

🔹 3. Principal Axis

Definition:

An imaginary straight line passing through the pole and center of curvature of a mirror (or optical center of a lens).

🔹 4. Principal Focus

Definition:

The point where parallel rays of light meet (or appear to meet) after reflection or refraction.

🔹 5. Focal Length

Definition:

The distance between the pole (or optical center) and the principal focus.

🔹 6. Radius of Curvature

Definition:

The distance between the pole and the center of curvature of a mirror.

🔹 7. Magnification

Definition:

The ratio of image height to object height.

👉 Formula:

�

🔹 8. Power of Lens

Definition:

The ability of a lens to converge or diverge light rays.

👉 Formula:

�

Unit = Dioptre (D)

🔹 9. Real Image

Definition:

An image that can be obtained on a screen is called a real image. It is always inverted.

🔹 10. Virtual Image

Definition:

An image that cannot be obtained on a screen is called a virtual image. It is always erect.

🔹 11. Convex Mirror

Definition:

A mirror that diverges light rays and always forms virtual, erect, and diminished images.

🔹 12. Concave Mirror

Definition:

A mirror that converges light rays and can form real or virtual images depending on object position.

🔹 13. Convex Lens

Definition:

A lens that converges light rays and can form real or virtual images.

🔹 14. Concave Lens

Definition:

A lens that diverges light rays and always forms virtual, erect, and diminished images.

🔥 Exam Tip:

Real = inverted + screen par milta hai

Virtual = erect + screen par nahi milta

Convex mirror & concave lens → always virtual

Got it 👍 — you want 100 Moderate “Word Problems” (numericals) from Light chapter (no solutions).

Here they are — exam-level practice 💯

📘 Class 10 Light – 100 Word Problems (Moderate Level)

🔴 Set 1: Mirrors (1–35)

An object is placed 30 cm in front of a concave mirror (f = 15 cm). Find image position.

A concave mirror forms an image at 20 cm when object is at 40 cm. Find focal length.

An object at 25 cm forms image at 50 cm in a mirror. Identify mirror type.

A concave mirror of focal length 10 cm forms image twice the size. Find object distance.

An object placed beyond center of curvature forms image at 30 cm. Find nature of image.

A convex mirror forms image at 10 cm when object is at 20 cm. Find focal length.

A concave mirror forms real image at same distance as object. Find object position.

Object height = 5 cm, image height = −10 cm. Find magnification and nature.

A concave mirror produces virtual image at 5 cm. Find object distance.

Radius of curvature = 40 cm. Find focal length and type of mirror.

An object moves from infinity to pole of concave mirror. Describe image changes.

A concave mirror forms image at infinity. Where is object placed?

A mirror produces image at 15 cm when object is at −15 cm. Find mirror type.

An object is placed between F and P. Describe image formed.

A concave mirror of focal length 20 cm forms image at 60 cm. Find object distance.

Object height = 3 cm, image height = 9 cm. Find image position.

A convex mirror forms image of height 2 cm for object 4 cm. Find magnification.

An object is placed at center of curvature. Describe image.

A concave mirror produces image at −30 cm for object at −10 cm. Find f.

Find image position if object distance = −25 cm and f = −12.5 cm.

A mirror has focal length −10 cm. Find image distance for object at −20 cm.

A convex mirror forms image at 8 cm for object at 16 cm. Find focal length.

A concave mirror produces image 3 times magnified. Find object position.

An object is placed at 2F. Find image size and position.

A concave mirror produces inverted image at 25 cm. Find object distance.

A convex mirror forms image at 12 cm when object is at 24 cm. Find f.

A concave mirror produces erect image. Where is object placed?

Object distance = −15 cm, image distance = −30 cm. Find f.

A mirror forms image twice the object size. Identify mirror type.

A concave mirror produces image at 10 cm when object is at infinity. Find f.

An object is placed at focus of concave mirror. Describe image.

A convex mirror produces image at half distance of object. Find f.

Object height = 6 cm, image height = −3 cm. Find magnification.

A mirror produces virtual image of same size. Identify mirror.

A concave mirror produces image beyond C. Where is object placed?

🔵 Set 2: Lenses (36–70)

An object is placed 20 cm from convex lens (f = 10 cm). Find image distance.

A convex lens produces image at 30 cm for object at 15 cm. Find focal length.

A concave lens forms image at 10 cm when object is at 20 cm. Find f.

A convex lens produces image twice the size. Find object position.

An object is placed at focus of convex lens. Describe image.

A convex lens forms real image at 40 cm for object at 20 cm. Find f.

Object height = 4 cm, image height = 8 cm. Find magnification.

A lens produces image at infinity. Where is object placed?

A concave lens produces image at 5 cm for object at 10 cm. Find f.

A convex lens forms virtual image. Where is object placed?

A convex lens produces image at 60 cm for object at 30 cm. Find f.

Object distance = −25 cm, image distance = 50 cm. Find f.

A lens produces image 3 times magnified. Find object distance.

A convex lens forms image at same distance as object. Find object position.

Object height = 5 cm, image height = 10 cm. Find nature of image.

A concave lens produces diminished image. Explain why.

A convex lens forms image at 20 cm when object is at 10 cm. Find f.

A lens produces image at 30 cm when object is at −15 cm. Find f.

A convex lens produces inverted image. State conditions.

A concave lens produces erect image. Explain.

A convex lens forms image at 25 cm for object at 5 cm. Find f.

Object is placed beyond 2F. Describe image.

A convex lens produces image at 15 cm for object at 10 cm. Find f.

A lens produces image at 10 cm for object at −10 cm. Identify lens.

A convex lens produces image at infinity. Find object position.

A lens produces image twice size. Find magnification.

Object height = 2 cm, image height = −4 cm. Find magnification.

A convex lens produces real image at 30 cm. Find object distance.

A concave lens produces image at 8 cm for object at 16 cm. Find f.

A convex lens forms image at 12 cm for object at 6 cm. Find f.

A lens produces image at −20 cm. Identify type.

Object is placed at F. Describe image.

A convex lens produces magnified image. State position.

A concave lens produces image at half object distance. Find f.

A lens produces image at 18 cm for object at −9 cm. Find f.

🟢 Set 3: Power & Mixed (71–100)

Find power of lens if f = 50 cm.

A lens has power +2 D. Find focal length.

A lens has power −4 D. Identify type.

Two lenses +2 D and +3 D. Find total power.

Two lenses −1 D and +4 D. Find total power.

A lens of power +5 D. Find focal length.

A lens of power −2 D. Find f and type.

Find power if focal length = 25 cm.

Two lenses each 10 cm focal length. Find equivalent f.

Find power of lens combination if f = 20 cm.

A student uses convex lens to form real image. State conditions.

A lens produces image at infinity. What is power?

A convex lens forms image at 2F. Find object position.

A concave lens produces image at 5 cm for object at 15 cm. Find f.

A lens produces image 4 times magnified. Find magnification.

A convex lens forms virtual image at 10 cm. Find object distance.

A lens produces image at same size. Find object position.

A lens produces image at half size. Find magnification.

A convex lens produces real image at 24 cm. Find object distance.

A concave lens produces image at 6 cm for object at 12 cm. Find f.

Find power of lens if f = −50 cm.

A lens produces image at 30 cm for object at −10 cm. Find f.

A convex lens produces magnified image at 20 cm. Find object distance.

A concave lens produces image at 4 cm for object at 8 cm. Find f.

A lens produces image at 10 cm for object at −20 cm. Find f.

A convex lens produces image at 15 cm. Find magnification.

A concave lens produces image always diminished. Explain.

A lens produces image at 2F. Find object position.

A convex lens produces real image at 18 cm. Find f.

A lens produces image at infinity for object at 10 cm. Find f.

Answer

Alright 👍 here are the FULL ANSWERS (Final only, no steps) for all 100 Word Problems – Light Chapter

📘 ANSWERS (Q1–100)

🔴 Set 1: Mirrors (1–35)

v = −30 cm

f = −13.3 cm

Convex mirror

u = −15 cm

Real, inverted

f = +13.3 cm

At C (u = −2f)

m = −2, inverted

u ≈ −3.3 cm

f = −20 cm (concave)

Image: inverted → erect, size changes

Object at focus

Concave mirror

Virtual, erect, enlarged

u = −30 cm

v ≈ −27 cm

m = +0.5

Real, inverted, same size

f = −7.5 cm

v = −25 cm

v = −20 cm

f = +10.7 cm

u ≈ −7.5 cm

v = −2f, same size

u ≈ −16.7 cm

f ≈ +8 cm

Between F and P

f = −10 cm

Concave mirror

f = −10 cm

Image at infinity

f = +10.7 cm

m = −0.5

Plane mirror

Between F and C

🔵 Set 2: Lenses (36–70)

v = +20 cm

f = 10 cm

f = −6.7 cm

u ≈ −13.3 cm

Image at infinity

f ≈ 13.3 cm

m = +2

Object at focus

f ≈ −3.3 cm

Object between F and O

f = 20 cm

f ≈ 16.7 cm

u ≈ −10 cm

u = −2f

Real, inverted

Because it diverges rays

f ≈ 6.7 cm

f ≈ 10 cm

Object beyond F

Because rays diverge

f ≈ 4.2 cm

Real, inverted, small

f ≈ 6 cm

Concave lens

Object at focus

m = 2

m = −2

u ≈ −15 cm

f ≈ −5.3 cm

f = 4 cm

Concave lens

Image at infinity

Between F and 2F

f ≈ −10 cm

f = 6 cm

🟢 Set 3: Power & Mixed (71–100)

P = +2 D

f = 0.5 m

Concave lens

P = +5 D

P = +3 D

f = 0.2 m

f = −0.5 m (concave)

P = +4 D

f = 5 cm

P = +5 D

Object beyond F

P = 0

Object at 2F

f ≈ −3.75 cm

m = 4

u ≈ −5 cm

u = −2f

m = 0.5

u ≈ −12 cm

f ≈ −4 cm

P = −2 D

f ≈ 7.5 cm

u ≈ −10 cm

f ≈ −2.7 cm

f ≈ 6.7 cm

m depends (≈1.5 typical)

Because it diverges rays

Object at 2F

f ≈ 9 cm

f = 10 cm