A concave mirror produces an image of an object such that the...

A concave mirror produces an image of an object such that the distance between the object and image is 20 cm . If the magnification of the image is ' -3 ', then the magnitude of the radius of curvature of the mirror is :

Options

A $30\mathrm{~cm}$
B $3.75\mathrm{~cm}$
C $15\mathrm{~cm}$
D $7.5\mathrm{~cm}$

Correct answer

C. $15\mathrm{~cm}$

Step-by-step solution

\begin{aligned} & m=-3=-\frac{u}{v} \\ & u=-x \\ & v=-3 x \\ & \Rightarrow 2 x=20 \mathrm{~cm}\end{aligned}

\begin{aligned} & x=10 \mathrm{~cm} \\ & f=\frac{u V}{u+V}=\frac{(-10)(-30)}{(-10)+(-30)}=-7.5 \mathrm{~cm} \\ & f=-\frac{R}{2} \\ & R=-2 f=15 \mathrm{~cm}\end{aligned}

Practice Ray Optics on Quantrex Academy →

More from Ray Optics

A double convex lens made of glass of refractive index 1.5 and radii of curvature of the… JEE Advanced 2026 A beam of polychromatic light passes through a thin prism of prism angle 6^∘ . The… JEE Advanced 2026 Consider two isosceles prisms 1 and 2 with prism angles A_1 and A_2 and refractive… JEE Advanced 2026 A thin biconvex lens is prepared from the glass ( μ=1.5 ) both curved surfaces of which… JEE Main 2026 Light ray incident along a vector AO ( AO = 2 i -3 j ) emerges out along vector OB ( OB =… JEE Main 2026 Angle of minimum deviation is equal to the half of the angle of prism in an equilateral… JEE Main 2026 A concave mirror of focal length 10 cm forms an image which is double the size of object… JEE Main 2026 A spherical interface lens of radius R separates two media of refractive indices 1 and… JEE Main 2026 Full Ray Optics list All JEE Main PYQs