JEE Main 2021 · PhysicsMultiple choiceSingle correctEasyRecall

JEE Main 24 February 2021, Shift 1, Physics Q19

Question 19 of 90 in this shift, Physics question 19 of 30, Section A.

The focal length

f

is related to the radius of curvature r of the spherical convex mirror by :

(1) $f=\mathrm{r}$
(2) $f=-\mathrm{r}$
(3) $f=-\frac{1}{2}\mathrm{r}$
(4) $f=+\frac{1}{2}\mathrm{r}$ Official answer

Official answer

Option 4

NTA final key.

Chapter: Ray Optics and Optical Instruments
Topic: Spherical Mirrors
Idea tested: Focal Length Relation

Same topic in other shifts

All Spherical Mirrors questions

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2 Apr 2025, Shift 2 · Q36Two identical objects are placed in front of convex mirror and concave mirror having same radii of curvature of 12 cm, at same distance of…MediumSingle correct
4 Apr 2025, Shift 2 · Q39A finite size object is placed normal to the principal axis at a distance of 30 cm from a convex mirror of focal length 30 cm. A plane…MediumSingle correct
7 Apr 2025, Shift 2 · Q40A mirror is used to produce an image with magnification of $\frac{1}{4}$ . If the distance between object and its image is 40 cm, then the…MediumSingle correct
29 Jan 2024, Shift 1 · Q49A convex mirror of radius of curvature 30 cm forms an image that is half the size of the object. The object distance is :EasySingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.