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A convex lense of focal length 40 cm is held coaxially 12 cm above a concave mirror of focal length18 cm. An object held x cm above the lens gives rise to an image coincident with it. The x is equal to.
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Important Questions on Physics

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General Studies>General Science>Physics>Optics
The power of a lens is –2.0 D. Here 'D' stands for:
EASY
General Studies>General Science>Physics>Optics
Which of the following is employed to clearly view objects which cannot be seen directly due to obstruction? 
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General Studies>General Science>Physics>Optics
Twinkling of stars is mainly due to which phenomena?
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General Studies>General Science>Physics>Optics
The power of a lens is measured in _____.
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General Studies>General Science>Physics>Optics
If an object is at 10 cm, away from the concave for which radius of curvature is 5 cm. Find out the value of magnification of the object:
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General Studies>General Science>Physics>Optics

Which one of the following is not a property of solution?

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General Studies>General Science>Physics>Optics
What will be the size of image formed by a concave mirror when an object placed between Pole and Focus?
MEDIUM
General Studies>General Science>Physics>Optics
The spectrum of light was first explained by _____
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General Studies>General Science>Physics>Optics
Dentist use Concave mirror because it gives _____ and _____ Image.
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General Studies>General Science>Physics>Optics
If the reflecting surface of a spherical minor is convex, then it is a _____ mirror.
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General Studies>General Science>Physics>Optics
The phenomenon of physics when, in polar regions like Alaska and Northern Canada, a splendid
display of colours is seen in the sky is called a/an:
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General Studies>General Science>Physics>Optics
Where should an object be placed in front of a convex lens to obtain a real image of the same size of the object?
MEDIUM
General Studies>General Science>Physics>Optics
The Tyndall Effect is due to
MEDIUM
General Studies>General Science>Physics>Optics
The phenomenon of deviation of light rays from their original path, when they pass from one medium to another, is called _____.
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General Studies>General Science>Physics>Optics
The sky appears blue due to _____.
MEDIUM
General Studies>General Science>Physics>Optics
Which scientific instrument is used to measure the height of an aircraft above a fixed level?
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General Studies>General Science>Physics>Optics
In which part of the human body will you find the 'superior rectus'?
EASY
General Studies>General Science>Physics>Optics
Which mirror has a very wide field of view?
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General Studies>General Science>Physics>Optics
After a shower of rain, a rainbow is seen:
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General Studies>General Science>Physics>Optics

If the focal length of a mirror is +15, then it is______: