JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
The size of the images of an object, formed by a thin lens are equal when the object is placed at two different positions 8 cm and 24 cm from the lens. The focal length of the lens is ___________ cm.
- A 12
- B 16
- C 18
- D 20
Answer & Solution
Correct Answer
(B) 16
Step-by-step Solution
Detailed explanation
\(m=\frac{f}{f+u}\) \(m _1=- m _2\) \(\frac{f}{f-8}=-\frac{f}{f-24}\) \(f-8=24-f\) \(2 f=32\) \(f =16 cm\)
See the Complete Solution
Get step-by-step explanations for this and 2.5 Lakh+ more JEE, NEET & CET questions.
- Unlock all solutions
- Practice the full chapter
- Track accuracy across PYQs
4.8 rated on Google Play · 14,000+ reviews
More questions from Physics
- In a certain region static electric and magnetic fields exist. The magnetic field is given by \(\vec B = {B_0}\left( {\hat i + 2\hat j - 4\hat k} \right)\). If a test charge moving with a velocity \(\vec v = {v_0}\left( {3\hat i - \hat j + 2\hat k} \right)\) experiences no force in that region, then the electric field in the region, in \(SI\, units\), isJEE Mains 2017 Medium
- A wire of resistance \(R\) and length \(L\) is cut into 5 equal parts. If these parts are joined parallely, then resultant resistance will be _______.JEE Mains 2024 Medium
- A body starts moving from rest with constant acceleration covers displacement \(S_1\) in first \((p-1)\) seconds and \(S_2\) in first \(p\) seconds. The displacement \(S_1+S_2\) will be made in time :JEE Mains 2024 Hard
- A passenger train of length \(60\, m\) travels at a speed of \(80\, km/hr\). Another freight train of length \(120\, m\) travels at a speed of \(30\, km/hr\). The ratio of times taken by the passenger train to completely cross the freight train when: \((i)\) they are moving in the same direction, and \((ii)\) in the opposite directions isJEE Mains 2019 Hard
- Three capacitors each of \(4\,\,\mu F\) are to be connected in such a way that the effective capacitance is \(6\,\,\mu F.\) This can be done by connecting thernJEE Mains 2016 Hard
- The electric field a plane electromagnetic wave is given by :
\(E _y=69 \sin \left[0.6 \times 10^3 x -1.8 \times 10^{11} t \right] V / m\).
The expression for magnetic field associated with this electromagnetic wave is _________ T.JEE Mains 2026 Hard
More PYQs from JEE Mains
- Let \(S=\{1,2,3,4,5,6\}\). Then the number of oneone functions \(f: S \rightarrow P(S)\), where \(P(S)\) denote the power set of \(S\), such that \(f(n) \subset f(m)\) where \(n < m\) is \(..................\)JEE Mains 2023 Hard
- Two equal sides of an isosceles triangle are along \(-x+2 y=4\) and \(x+y=4\). If m is the slope of its third side, then the sum, of all possible distinct values of \(m\), is :JEE Mains 2025 Medium
- The distance of the point \((1, 0, 2)\) from the point of intersection of the line \(\frac{{x - 2}}{3} = \frac{{y + 1}}{4} = \frac{{z - 2}}{{12}}\) and the plane \(x - y + z = 16\) isJEE Mains 2015 Medium
- Consider a uniform rod of mass \(\mathrm{M}=4 \mathrm{m}\) and length \(\ell\) pivoted about its centre. A mass \(m\) moving with velocity \(v\) making angle \(\theta=\frac{\pi}{4}\) to the rod's long axis collides with one end of the rod and sticks to it. The angular speed of the rod-mass system just after the collision isJEE Mains 2020 Hard
- 10 kg of ice at \(-10^{\circ}C\) is added to 100 kg of water to lower its temperature from \(25^{\circ}C.\) Consider no heat exchange to surroundings. The decrement to the temperature of water is ___________ \(^{\circ}C.\)
(specific heat of ice \(= 2100\ J/Kg.^{\circ}C\), specific heat of water \(= 4200\ J/Kg.^{\circ}C\), latent heat of fusion of ice \(= 3.36 \times 10^{5}\ J/Kg\))JEE Mains 2026 Hard - A monoatomic gas of mass \(4.0\, u\) is kept in an insulated container. Container is moving with velocity \(30 \,m / s\). If container is suddenly stopped then change in temperature of the gas \(\left( R =\right.\) gas constant) is \(\frac{ x }{3 R } .\) Value of \(x\) is ..........JEE Mains 2021 Hard