Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board held close to the mirror. Move the card-board back and forth gradually until you find a bright, sharp spot of light on the board. This spot of light is the image of the sun on the sheet of paper; which is also termed as "Principal Focus" of the concave mirror. (a) List two applications of concave mirror. (b) If the distance between the mirror and the principal focus is $15 \mathrm{cm}$, find the radius of curvature of the mirror. (c) Draw a ray diagram to show the type of image formed when an object is placed between pole and focus of a concave mirror. OR (c) An object $10 \mathrm{cm}$ in size is placed at $100 \mathrm{cm}$ in front of a concave mirror. If its image is formed at the same point where the object is located, find: (i) focal length of the mirror, and (ii) magnification of the image formed with sign as per Cartesian sign convention.

The two applications of concave mirror are: (a) Concave mirrors are used as shaving mirrors to see a larger image of the face being shaved. (b) Concave mirrors are used by dentists to focus light on teeth. The radius of curvature of the mirror is twice the focal length, so it is $30 \mathrm{cm}$. The ray diagram for an object placed between pole and focus of a concave mirror is shown below. The image formed is virtual, erect, and magnified. OR The focal length of the mirror is $50 \mathrm{cm}$, and the magnification of the image formed is $-1$.

Question 394 marksSection E

$15 \mathrm{cm}$

Light — Reflection and Refraction

Reflection of Light

Official answer

30 \mathrm{cm}

concave mirror

shaving mirror

dentist

radius of curvature

focal length

ray diagram

virtual image

erect image

magnified image

Marking scheme

1. $(a) Concave mirrors are used as shaving mirrors to see a larger image of the face being shaved.$
2. $(b) Concave mirrors are used by dentists to focus light on teeth.$
3. $30 \mathrm{cm}$
4. $The ray diagram for an object placed between pole and focus of a concave mirror is shown below. The image formed is virtual, erect, and magnified.$
5. $50 \mathrm{cm}$

Hint

$30 \mathrm{cm}$

Quick oral answer

$30 \mathrm{cm}$

Common mistakes

1. $Confusing concave mirrors with convex mirrors.$
2. $Not understanding the difference between focal length and radius of curvature.$
3. $Not being able to draw the correct ray diagram for an object placed between pole and focus of a concave mirror.$

Analysis and explanation

30 \mathrm{cm}

Interesting facts

$Concave mirrors are used in telescopes to magnify distant objects.$

$Concave mirrors are used in solar concentrators to focus sunlight onto a small area.$

$Concave mirrors are used in laser technology to focus laser beams.$

Question details

Q39 of 39 questions

Board: CBSE
Class: Class 10
Subject: Science
Year: 2023
Section: Section E
Marks: 4
Chapter: Light — Reflection and Refraction
Topic: $Reflection of Light$
Bloom's level: Understanding
Syllabus topic: $Reflection of Light$

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Frequently asked questions

$How many marks does this question carry in CBSE Class 10 Science 2023?$

$This question carries 4 marks in the CBSE Class 10 Science 2023 examination.$

$Which chapter does this question come from in Science?$

$This question is from the chapter "Light — Reflection and Refraction" in the CBSE Class 10 Science syllabus.$

$What topic does this question cover in Science?$

$This question covers the topic "Reflection of Light" from CBSE Class 10 Science.$

$What type of question is this in the CBSE Class 10 Science 2023 paper?$

$This question appears in Section E in the CBSE Class 10 Science 2023 paper.$