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A: Owl can move easily at night time. ...

A: Owl can move easily at night time.
R : There are so many rods in the retina in The eye of owl.

A

Both assertion and reason are true and the reason is correct explanation of the assertion.

B

Both assertion and reason are true but reason is not correct explanation of the assertion

C

Assertion is true but the reason is false.

D

Both assertion and reason are false.

Text Solution

Verified by Experts

The correct Answer is:
A
Both assertion and reason are true and the reason is correct explanation of the assertion.
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The ciliary muscles of eye control the curvature of the lens in the eye and hence can alter the effective focal length of the system. When the muscles are fully relaxed, the focal length is maximum. When the muscles are strained, the curvature of lens increases. That means radius of curvature decreases and focal length decreases. For a clear vision, the image must be on the retina. The image distance is therefore fixed for clear vision and it equals the distance of retina from eye lens. It is about 2.5cm for a grown up person. A perosn can theoretically have clear vision of an object situated at any large distance from the eye. The smallest distance at which a person can clearly see is related to minimum possible focal length. The ciliary muscles are most strained in this position. For an average grown up person, minimum distance of the object should be around 25cm. A person suffering from eye defects uses spectacles (eye glass). The function of lens of spectacles is to form the image of the objects within the range in which the person can see clearly. The image o the spectacle lens becomes object for the eye lens and whose image is formed on the retina. The number of spectacle lens used for th eremedy of eye defect is decided by the power fo the lens required and the number of spectacle lens is equal to the numerical value of the power of lens with sign. For example, if power of the lens required is +3D (converging lens of focal length 100//3cm ), then number of lens will be +3 . For all the calculations required, you can use the lens formula and lensmaker's formula. Assume that the eye lens is equiconvex lens. Neglect the distance between the eye lens and the spectacle lens. Q. Maximum focal length of a eye lens of a normal person is

The ciliary muscles of eye control the curvature of the lens in the eye and hence can alter the effective focal length of the system. When the muscles are fully relaxed, the focal length is maximum. When the muscles are strained, the curvature of lens increases. That means radius of curvature decreases and focal length decreases. For a clear vision, the image must be on the retina. The image distance is therefore fixed for clear vision and it equals the distance of retina from eye lens. It is about 2.5cm for a grown up person. A perosn can theoretically have clear vision of an object situated at any large distance from the eye. The smallest distance at which a person can clearly see is related to minimum possible focal length. The ciliary muscles are most strained in this position. For an average grown up person, minimum distance of the object should be around 25cm. A person suffering from eye defects uses spectacles (eye glass). The function of lens of spectacles is to form the image of the objects within the range in which the person can see clearly. The image o the spectacle lens becomes object for the eye lens and whose image is formed on the retina. The number of spectacle lens used for th eremedy of eye defect is decided by the power fo the lens required and the number of spectacle lens is equal to the numerical value of the power of lens with sign. For example, if power of the lens required is +3D (converging lens of focal length 100//3cm ), then number of lens will be +3 . For all the calculations required, you can use the lens formula and lensmaker's formula. Assume that the eye lens is equiconvex lens. Neglect the distance between the eye lens and the spectacle lens. Q. Maximum focal length of a eye lens of a normal person is

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KUMAR PRAKASHAN-RAY OPTICS AND OPTICAL INSTRUMENTS-SECTION-D (MULTIPLE CHOICE QUESTIONS (MCQs))(MCQs ASKED IN COMPETITIVE EXAMS)
  1. Two lenses of focal lengths -20 cm and + 10 cm are conneceted to form ...

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  2. A: Stars twinkle in sky at night, planets don.t. R: Volume of star...

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  3. A: Owl can move easily at night time. R : There are so many rods i...

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  4. A: Red substance seems to be black in presence of yellow light. R:...

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  5. A: Transperency of glass decreases if its surface becomes rough. R...

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  6. A: Diamond glitters. R: Diamond doesn.t absorb sun light.

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  7. A: Resolution of telescope is high if diameter of objective is large. ...

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  8. A: Power of lens of goggles is zero. R: Radii of curvature of both...

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  9. A: If objective and eye-piece of compoun microcscope are interchanged,...

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  10. A: When white light passes through lens then refraction of violet ligh...

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  11. A: Magnified image is obtained by microscope. R: Angular dispersio...

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  12. A: Magnification for convex mirror is always positive where it may be ...

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  13. A spherical mirror gives real image 3 times greater than object. If di...

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  14. Focal length of plane mirror is ......

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  15. A light of ray incidents normally on one side of equilateral prism. If...

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  16. Two thin lenses of focal lengths f1 and f2, are in contact and coaxial...

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  17. The colour of rays is the property of ......

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  18. A critical angle for a medium is 60^@. Then the refractive index of th...

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  19. A wavelength of a monochromatic light in vacuum is lambda . It travels...

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  20. An object is placed at a distance 40 cm in front of concave mirror. Fo...

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