Advertisements
Advertisements
प्रश्न
A normal eye is not able to see objects closer than 25 cm because
विकल्प
the focal length of the eye is 25 cm
the distance of the retina from the eye-lens is 25 cm
the eye is not able to decrease the distance between the eye-lens and the retina beyond a limit
the eye is not able to decrease the focal length beyond a limit.
Advertisements
उत्तर
the eye is not able to decrease the focal length beyond a limit
The ciliary muscles adjust the focal length to form an image on the retina, but the muscles cannot be strained beyond a limit. Hence, if the object is brought too close to the eye, the focal length cannot be adjusted to form the image on the retina.
APPEARS IN
संबंधित प्रश्न
Calculate the focal length of a corrective lens having power +2D.
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
The focal length of a convex lens is 25 cm. What is its power?
The power of a lens is + 0.2 D. Calculate its focal length.
What is the nature of a lens whose power is, −4 D?
What is the unit of power of a lens? Define the unit of power of a lens.
A converging lens has a focal length of 50 cm. The power of this lens is:
The power of a lens is +2.0D. Its focal length should be :
State the condition for the following a ray passes undeviated through the lens .
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
A symmetric double convex lens is cut in two equal parts by a plane containing the principal axis. If the power of the original lens was 4 D, the power of a divided lens will be
Consider the situation described in the previous problem. Where should a point source be placed on the principal axis so that the two images form at the same place?
If there is a convex lens of focal length 75 cm and a concave lens of focal length 40 cm, then calculate their combined power and combined focal length.
The power of the magnifying glass depends on the distance of the magnifying glass from object.
The power of lens depends on the focal length of the lens
Increase in the converging power of eye lens cause ‘hypermetropia'
Match the following:
| Column - I | Column - II | ||
| 1 | Retina | a | Path way of light |
| 2 | Pupil | b | Far point comes closer |
| 3 | Ciliary muscles | c | near point moves away |
| 4 | Myopia | d | Screen of the eye |
| 5 | Hypermetropia | e | Power of accommodation |
An object is placed in front of a converging lens. Obtain the conditions under which the magnification produced by the lens is
- negative and
- positive.
An object is kept at a distance of 1m from a lens of power +2D:
- Identify the type of lens.
- Calculate its focal length and distance of the image formed.
