Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Geometrical Optics question

2022 · 28 Jul · Shift 2 · Q64
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Geometrical Optics
  5. /2022 · 28 Jul · Shift 2 · Q64

Geometrical Optics question

2022 · 28 Jul · Shift 2 · Q64

JEE MainPhysicsGeometrical OpticsNumerical+4 / −1
An object 'O' is placed at a distance of 100 cm100 \mathrm{~cm}100 cm in front of a concave mirror of radius of curvature 200 cm200 \mathrm{~cm}200 cm as shown in the figure. The object starts moving towards the mirror at a speed 2 cm/s2 \mathrm{~cm} / \mathrm{s}2 cm/s. The position of the image from the mirror after 10 s10 \mathrm{~s}10 s will be at ‾\underline{\hspace{2cm}}​cm\mathrm{cm}cm. JEE Main 2022 (Online) 28th July Evening Shift Physics - Geometrical Optics Question 98 English
Numerical answer
View written solutionFree

Correct answer: 400

  1. Given data
  • Radius of curvature of concave mirror: R=200 cmR = 200\,\text{cm}R=200cm
  • Hence focal length: f=R2=100 cmf = \frac{R}{2} = 100\,\text{cm}f=2R​=100cm

For a concave mirror, using Cartesian sign convention: f=−100 cmf = -100\,\text{cm}f=−100cm

  • Initial object distance: 100 cm100\,\text{cm}100cm in front of mirror u0=−100 cmu_0 = -100\,\text{cm}u0​=−100cm

  • Object moves towards the mirror with speed 2 cm/s2\,\text{cm/s}2cm/s for 10 s10\,\text{s}10s

So in 10 s10\,\text{s}10s, object moves: s=vt=2×10=20 cms = vt = 2 \times 10 = 20\,\text{cm}s=vt=2×10=20cm

Thus new object distance is: u=−(100−20)=−80 cmu = -(100 - 20) = -80\,\text{cm}u=−(100−20)=−80cm


  1. Use mirror formula

Mirror formula: 1f=1v+1u\frac{1}{f} = \frac{1}{v} + \frac{1}{u}f1​=v1​+u1​

Substitute f=−100 cmf=-100\,\text{cm}f=−100cm and u=−80 cmu=-80\,\text{cm}u=−80cm: 1−100=1v+1−80\frac{1}{-100} = \frac{1}{v} + \frac{1}{-80}−1001​=v1​+−801​

−1100=1v−180-\frac{1}{100} = \frac{1}{v} - \frac{1}{80}−1001​=v1​−801​

So, 1v=−1100+180\frac{1}{v} = -\frac{1}{100} + \frac{1}{80}v1​=−1001​+801​

Take LCM 400400400: 1v=−4+5400=1400\frac{1}{v} = \frac{-4+5}{400} = \frac{1}{400}v1​=400−4+5​=4001​

Therefore, v=400 cmv = 400\,\text{cm}v=400cm


  1. Interpretation

The positive sign of vvv means the image is formed behind the mirror (virtual image), at a distance of 400 cm400\,\text{cm}400cm from the mirror.


  1. Final answer

The position of the image after 10 s10\,\text{s}10s is: 400 cm\boxed{400\,\text{cm}}400cm​

PreviousNext

More from Geometrical Optics

  • In an experiment with a convex lens, The plot of the image distance (v′) against the object distance (μ′) measured from the focus gives a curve v′μ′=225. If all the…2022 · Numerical
  • The refracting angle of a prism is A and refractive index of the material of the prism is cot (A/2). Then the angle of minimum deviation will be -2022 · MCQ
  • The aperture of the objective is 24.4 cm. The resolving power of this telescope, if a light of wavelength 2440 Ao​ is used to see th object will be :2022 · MCQ
  • The X-Y plane be taken as the boundary between two transparent media M1​ and M2​. M1​ in Z⩾0 has a refractive index of 2​ and M2​ with Z<0 has a refractive index of 3​…2022 · Numerical
  • Light enters from air into a given medium at an angle of 45∘ with interface of the air-medium surface. After refraction, the light ray is deviated through an angle of 15∘ from its original direction. The refractive index…2022 · MCQ
  • A parallel beam of light is allowed to fall on a transparent spherical globe of diameter 30 cm and refractive index 1.5. The distance from the centre of the globe at which the beam of light can converge is ​ mm.2022 · Numerical
  • The speed of light in media 'A' and 'B' are 2.0×1010 cm/s and 1.5×1010 cm/s respectively. A ray of light enters from the medium B to A at an incident angle 'θ'. If the ray suffers total internal…2022 · MCQ
  • The refractive index of an equilateral prism is 2​. The angle of emergence under minimum deviation position of prism, in degree, is ​.2022 · Numerical