Lens Fact: The focal length of a convex lens is positive, while that of a concave lens is negative. This sign convention helps determine the nature and position of images formed by lenses.
Optical Elements: Principal Axis | Optical Center | Principal Focus | Focal Length
📘 Subject: Science Part 1
📗 Chapter 7: Lenses
🎓 Class: 10 (Maharashtra Board)
✅ Status: Original & Copyright-Free
Very Short Answer Questions
1–2 Marks Each
Define a lens.
Basic Definition
Name two types of lenses.
Lens Types
What is the principal focus of a lens?
Optical Term
Define focal length.
Key Definition
Write the lens formula.
Fundamental Formula
1/f = 1/v - 1/u
What is magnification?
Image Property
Which type of lens converges light?
Lens Property
Which type of lens diverges light?
Lens Property
Give one use of a convex lens.
Application
Give one use of a concave lens.
Application
Short Answer Questions
3–4 Marks Each
Draw a ray diagram to show image formation by a convex lens when the object is beyond 2F.
Ray Diagram - Convex Lens
Object beyond 2F → Image between F and 2F (real, inverted, diminished)
Draw a ray diagram for a convex lens when the object is between F and 2F.
Ray Diagram - Convex Lens
Object between F and 2F → Image beyond 2F (real, inverted, magnified)
Draw a ray diagram for a concave lens and label the image.
Ray Diagram - Concave Lens
Concave lens → Image between F and optical center (virtual, erect, diminished)
State and explain the sign conventions used in lenses.
Sign Convention Rules
Derive the lens formula relating u, v, and f.
Formula Derivation
Explain the types of images formed by a convex lens with examples.
Image Types - Convex Lens
Object Position
Image Type
Example
Beyond 2F
Real, Inverted, Diminished
Camera
Between F & 2F
Real, Inverted, Magnified
Projector
Between F & O
Virtual, Erect, Magnified
Magnifying Glass
Explain the properties of the image formed by a concave lens.
Image Properties - Concave Lens
Explain magnification and its formula with examples.
Magnification Concept
m = h'/h = -v/u
Explain combination of two lenses in contact and the resulting focal length.
Lens Combination
1/F = 1/f₁ + 1/f₂
Why is a concave lens used in spectacles for myopia?
Application - Myopia Correction
Long Answer Questions
5 Marks Each
Explain image formation by convex lens for different positions of the object.
Comprehensive Explanation
Draw and explain ray diagrams for a concave lens.
Concave Lens Ray Diagrams
Derive the lens formula and explain each term.
Formula Derivation & Explanation
Explain magnification and how it affects the size of image.
Magnification Analysis
Describe applications of convex and concave lenses in daily life.
Real-life Applications
Numerical / Application-Based Questions
Problem Solving
Calculate the focal length of a lens when object and image distances are given.
Focal Length Calculation
1/f = 1/v - 1/u
Find the image distance using lens formula for a given object distance and focal length.
Image Distance Calculation
1/v = 1/f + 1/u
Calculate magnification of an image when object and image distances are given.
Magnification Calculation
m = -v/u
Determine the type of lens required to correct myopia or hypermetropia.
Vision Correction Application
Solve problems involving combination of two lenses in contact.
Lens Combination Problems
Reasoning-Based Questions
Conceptual Understanding
Why does a convex lens produce a virtual image when the object is between F and the optical center?
Virtual Image Reasoning
Why is a concave lens always used to produce diminished images?
Image Size Reasoning
Why do cameras use convex lenses to focus light on film?
Camera Optics Reasoning
Why is the image formed by a concave lens always erect?