Distance between virtual image, which is twice the size of object placed in front of mirror and object is 45 cm. The magnitude of focal length of the mirror is _____cm.
Solution and Explanation
The Correct Answer is : 30
\(|m|=|\frac{v}{u}|=2\)
\(|v|=|2u|\)
n + 2n = 45
n = 15 cm
u = –15
v = 30
\(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)
\(\frac{1}{30}+\frac{1}{-15}=\frac{1}{f}\)
\(\frac{1-2}{30}=\frac{-1}{30}=\frac{1}{f}\)
\(⇒ f=30\ cm\)
Top Questions on Spherical Mirrors
- 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:
- JEE Main - 2025
- Physics
- Spherical Mirrors
- (ii) An object at a distance of 16 cm from a spherical mirror forms a virtual image at a distance of 12 cm behind the mirror. Determine the magnification of the image and type of the mirror.
- UP Board X - 2025
- Science
- Spherical Mirrors
- Image of an object formed by a concave mirror is real and of the size of the object. The object is placed -
- UP Board X - 2025
- Science
- Spherical Mirrors
- With the help of a suitable ray diagram, derive the formula \( \frac{1}{v} + \frac{1}{u} = \frac{1}{f} \) for a concave mirror.
- UP Board XII - 2025
- Physics
- Spherical Mirrors
- The length of the image formed by a concave mirror:
- UP Board XII - 2025
- Physics
- Spherical Mirrors
Questions Asked in JEE Main exam
- Let $\vec{a}=2\hat{i}-\hat{j}-\hat{k}$, $\vec{b}=\hat{i}+3\hat{j}-\hat{k}$ and $\vec{c}=2\hat{i}+\hat{j}+3\hat{k}$. Let $\vec{v}$ be the vector in the plane of $\vec{a}$ and $\vec{b}$, such that the length of its projection on the vector $\vec{c}$ is $\dfrac{1}{\sqrt{14}}$. Then $|\vec{v}|$ is equal to
- JEE Main - 2026
- Vector Algebra
A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass = 300 g mol$^{-1}$) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is $____________ \(\times 10^{-2}\). (nearest integer)
[Given : $K_{b}$ of the solvent = 5.0 K kg mol$^{-1}$]
Assume the solution to be dilute and no association or dissociation of X takes place in solution.- JEE Main - 2026
- Solutions
- The wavelength of photon 'A' is 400 nm. The frequency of photon 'B' is \(10^{16}\,\text{s}^{-1}\). The wave number of photon 'C' is \(10^{5}\,\text{cm}^{-1}\). The correct order of energy of these photons is:
- JEE Main - 2026
- General Chemistry
- Given below are two statements: Statement I: The increasing order of boiling point of hydrogen halides is HCl<HBr<HI<HF. Statement II: The increasing order of melting point of hydrogen halides is HCl<HBr<HF<HI. In the light of the above statements, choose the correct answer from the options given below:
- JEE Main - 2026
- General Chemistry
Inductance of a coil with \(10^4\) turns is \(10\,\text{mH}\) and it is connected to a DC source of \(10\,\text{V}\) with internal resistance \(10\,\Omega\). The energy density in the inductor when the current reaches \( \left(\frac{1}{e}\right) \) of its maximum value is \[ \alpha \pi \times \frac{1}{e^2}\ \text{J m}^{-3}. \] The value of \( \alpha \) is _________.
\[ (\mu_0 = 4\pi \times 10^{-7}\ \text{TmA}^{-1}) \]- JEE Main - 2026
- Ray optics and optical instruments
Concepts Used:
Spherical Mirrors
A spherical mirror is a mirror which has been cut out of a spherical surface.
There are two kinds of spherical mirrors:
- Convex Mirror
- Concave Mirror
Concave Mirror
Concave mirrors are also called converging mirrors, because in these types of mirrors, light rays converge at a point after impact and reflect back from the reflective surface of the mirror.
Convex Mirror
The convex mirror has a reflective surface that is curved outward. Regardless of the distance between the subject and the mirrors, these mirrors are "always" virtual, upright and reduced.