Ray Optics And Optical Instruments

Question

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For a given lens, the magnification was found to be
twice as large as when the object was 0.15 m
distant from it as when the distance was 0.2 m. The
focal length of the lens is

1.5 m

0.20 m

0.10 m

0.05 m

Solution

0.20 m

Let as shown, 1 and 2 are positions of objects and
images in two different situations.

It is given

$|\frac{v_{1}}{u_{1}}| = 2 |\frac{v_{2}}{u_{2}}|$

Here, u₁ = -15 cm, u₂= -20 cm

$v_{1} = 2 v_{2} \times \frac{u_{1}}{u_{2}}$

= $2 v_{2} \times \frac{15}{20}$

$v_{1} = \frac{3}{2} v_{2}$

Now, $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$

$\frac{1}{f} = \frac{1}{v_{1}} - \frac{1}{u_{1}}$

$\frac{1}{f} = \frac{1}{v_{2}} - \frac{1}{u_{2}}$

So, $\frac{1}{v_{1}} - \frac{1}{u_{1}} = \frac{1}{v_{2}} - \frac{1}{u_{2}}$

⇒ $\frac{2}{3 v_{2}} + \frac{1}{15} = \frac{1}{v_{2}} + \frac{1}{20}$

⇒ v = 20 cm

⇒ v = 0.20 m

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Ray Optics And Optical Instruments

For a given lens, the magnification was found to be
twice as large as when the object was 0.15 m
distant from it as when the distance was 0.2 m. The
focal length of the lens is

1.5 m

0.20 m

0.10 m

0.05 m

Some More Questions From Ray Optics and Optical Instruments Chapter

Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.

Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.

Explain two advantages of a reflecting telescope over a refracting telescope.

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For Daily Free Study Material Join wiredfaculty

Ray Optics And Optical Instruments

For a given lens, the magnification was found to betwice as large as when the object was 0.15 mdistant from it as when the distance was 0.2 m. Thefocal length of the lens is 1.5 m 0.20 m 0.10 m 0.05 m

Some More Questions From Ray Optics and Optical Instruments Chapter

Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.

Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.

Explain two advantages of a reflecting telescope over a refracting telescope.

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distance are measured by

Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

For a given lens, the magnification was found to be
twice as large as when the object was 0.15 m
distant from it as when the distance was 0.2 m. The
focal length of the lens is

1.5 m

0.20 m

0.10 m

0.05 m