# CBSE Guess Sample Questions | Class 10, LIGHT - REFLECTION AND REFRACTION | Solutions of Ncert Science - Physics | CBSE Notes, Important Questions

## 10th NCERT Science Physics - CBSE Guess & Guide

### CBSE NCERT Solution - Physics (Science) – Notes, Study Materials

LESSON 3 of 3

#### Light – Reflection and Refraction:

Image Formation by a Convex Lens
(Table followed by figures)
 Position of the object Position of the image Size of image Nature of image 1 At infinity At focus F2 Highly diminished, point sized Real, inverted 2 Beyond 2F1 Between F2 and 2F2 Diminished Real, inverted 3 At 2F1 At 2F2 Same size Real, inverted 4 Between F1 and 2F1 Beyond 2F2 Enlarged Real, inverted 5 At focus F1 At infinity Infinitely large or highly enlarged Real, inverted 6 Between focus F1 and optic center O On the same side of the lens as the object Enlarged Virtual, erect

Image Formation by a Concave Lens
(Table followed by figures)
 Position of object Position of image Size of image Nature of image 1 At the infinity At focus F1 Highly diminished, point-sized Virtual, erect. 2 Between infinity and optical center of the lens Between focus F1 and optical center O. Diminished Virtual, erect.
Sign Convention (Spherical Lenses)
The following table summarizes the New Cartesian Sign Convention for spherical lenses:
 Lens Distance of object (u) Distance of image (v) Focal length (f) Height of object Height of image Real image Virtual image Real image Virtual image Convex – ve + ve – ve + ve + ve – ve + ve Concave – ve – ve – ve + ve + ve

CBSE Guess and Guide Sample Questions
Question.1: What are the differences between a spherical mirror and a lens?
Ans: The differences between a spherical mirror and a lens are listed below:
Spherical Mirror
• In a spherical mirror image is formed by reflection of light.
• t has a single focus.
• The center of the spherical mirror is known by the term Pole.
Spherical Lens
• Here image is formed by refraction of light.
• It has two foci.
• The center of the spherical mirror is known by the term Optical Center.
Question.2: For which colour the refractive index of material is the maximum?
Ans: For violet colour the refractive index of material is the maximum.
Question.3: Will there be any change in focal length of a concave mirror or concave lens when it is dipped in water?
Ans: No, because the focal length is independent of the refractive index of the material of mirror (or lens) and surrounding medium.
Question.4: When light undergoes refraction, what happens to its wavelength, frequency?
Ans: Wavelength of light decreases on entering a denser medium and increases on entering a rarer medium. Frequency of light will remain same.
Question.5: What is the focal length of a plane mirror?
Ans: It is infinity, as the plane mirror is considered to be part of a spherical mirror whose radius is infinite.
Question.6: What is the magnification produced by a plane mirror?
Ans: The magnification produced by a plane mirror is +1.
Question.7: What is the emergent angle of light after refraction in a glass slab?
Ans: The direction of the light after refraction in a glass slab will be parallel to the incident ray of light. Hence, the emergent angle will be equal to the angle of incidence.
Question.8: Magnification (m) of a plane mirror is +1. What does 1 and +ve sign signify?
Ans: m = +1 signify that image is erect, virtual and of equal size.
Question.9: Why is convex lens used in magnifying glass? Or, What is magnifying glass?
Ans: A magnifying glass is used to read small prints or see very small things. A convex lens produces virtual, erect and magnified image of an object when it is placed close to the lens. Because of this property of the convex lens it is used in magnifying glass to view magnified image of the objects.
Question.10: Why a concave lens is called diverging lens?
Ans:
Fig: Diverging Lens
When a beam of light parallel to the principal axis falls on a concave lens then they appear to be diverging from a single point, also known as principal focus (F) of the lens. Therefore, a concave lens is also known as Diverging Lens.