In the given case, the person is able to see vertical lines more distinctly than horizontal lines. This means that the refracting system (cornea and eye-lens) of the eye is not working in the same way in different planes. This defect is called astigmatism. The person’s eye has enough curvature in thRead more
In the given case, the person is able to see vertical lines more distinctly than horizontal lines. This means that the refracting system (cornea and eye-lens) of the eye is not working in the same way in different planes. This defect is called astigmatism. The person’s eye has enough curvature in the vertical plane. However, the curvature in the horizontal plane is insufficient. Hence, sharp images of the vertical lines are formed on the retina, but horizontal lines appear blurred. This defect can be corrected by using cylindrical lenses.
The power of the spectacles used by the myopic person, P = -1.0 D Focal length of the spectacles, f = 1/P =1/(-1 x 10⁻² ) = —100 cm Hence, the far point of the person is 100 cm. He might have a normal near point of 25 cm. When he uses the spectacles, the objects placed at infinity produce virtual iRead more
The power of the spectacles used by the myopic person, P = -1.0 D
Focal length of the spectacles, f = 1/P =1/(-1 x 10⁻² ) = —100 cm
Hence, the far point of the person is 100 cm. He might have a normal near point of 25 cm. When he uses the spectacles, the objects placed at infinity produce virtual images at 100 cm. He uses the ability of accommodation of the eye-lens to see the objects placed between 100 cm and 25 cm.
During old age, the person uses reading glasses of power, P’ = +2 D
The ability of accommodation is lost in old age. This defect is called presbyopia. As a result, he is unable to see clearly the objects placed at 25 cm.
A myopic or hypermetropic person can also possess the normal ability of accommodation of the eye-lens. Myopia occurs when the eye-balls get elongated from front to back. Hypermetropia occurs when the eye-balls get shortened. When the eye- lens loses its ability of accommodation, the defect is calledRead more
A myopic or hypermetropic person can also possess the normal ability of accommodation of the eye-lens. Myopia occurs when the eye-balls get elongated from front to back. Hypermetropia occurs when the eye-balls get shortened. When the eye- lens loses its ability of accommodation, the defect is called presbyopia
Least distance of distinct vision, d = 25 cm Far point of a normal eye, d' = ∝ Converging power of the cornea, Pc = 40 D Least converging power of the eye-lens, Pe = 20 D To see the objects at infinity, the eye uses its least converging power. Power of the eye-lens, P = Pc + Pe = 40 + 20 = 60 D PoweRead more
Least distance of distinct vision, d = 25 cm
Far point of a normal eye, d’ = ∝
Converging power of the cornea, Pc = 40 D
Least converging power of the eye-lens, Pe = 20 D
To see the objects at infinity, the eye uses its least converging power.
Power of the eye-lens, P = Pc + Pe = 40 + 20 = 60 D Power of the eye-lens is given as:
P= 1/Focal length of the eye lens (f)
f =1/P = 1/60D = 100/60 = 5/3 cm
To focus an object at the near point ,object distance (u) = -d = -25 cm
Focal length of the eye lens = Distance between the cornea and the retina = Image distance
Hence, image distance ,v = 5/3 cm
According to the lens formula ,we can write:
1/f” =1/v + 1/u
Where ,f” = focal length
1/f” = 3/5 + 1/25 = (15+1)/25 = 16/25 cm⁻¹
Power, P’ = 1/f ‘ x 100
= 16/25 x 100 = 64D
Therefor power of the eye-lens = 64-40=24D
Hence ,the range of accommodation of the eye-lens is from 20D to 24D
(a).Place the two prisms beside each other. Make sure that their bases are on the opposite sides of the incident white light, with their faces touching each other. When the white light is incident on the first prism, it will get dispersed. When this dispersed light is incident on the second prism, iRead more
(a).Place the two prisms beside each other. Make sure that their bases are on the opposite sides of the incident white light, with their faces touching each other. When the white light is incident on the first prism, it will get dispersed. When this dispersed light is incident on the second prism, it will recombine and white light will emerge from the combination of the two prisms.
(b).Take the system of the two prisms as suggested in answer (a). Adjust (increase) the angle of the flint-glass-prism so that the deviations due to the combination of the prisms become equal. This combination will disperse the pencil of white light without much deviation.
A person looking at a person wearing a shirt with a pattern comprising vertical and horizontal lines is able to see the vertical lines more distinctly than the horizontal ones. What is this defect due to? How is such a defect of vision corrected?
In the given case, the person is able to see vertical lines more distinctly than horizontal lines. This means that the refracting system (cornea and eye-lens) of the eye is not working in the same way in different planes. This defect is called astigmatism. The person’s eye has enough curvature in thRead more
In the given case, the person is able to see vertical lines more distinctly than horizontal lines. This means that the refracting system (cornea and eye-lens) of the eye is not working in the same way in different planes. This defect is called astigmatism. The person’s eye has enough curvature in the vertical plane. However, the curvature in the horizontal plane is insufficient. Hence, sharp images of the vertical lines are formed on the retina, but horizontal lines appear blurred. This defect can be corrected by using cylindrical lenses.
See lessA myopic person has been using spectacles of power -1.0 dioptre for distant vision. During old age he also needs to use separate reading glass of power + 2.0 dioptres. Explain what may have happened.
The power of the spectacles used by the myopic person, P = -1.0 D Focal length of the spectacles, f = 1/P =1/(-1 x 10⁻² ) = —100 cm Hence, the far point of the person is 100 cm. He might have a normal near point of 25 cm. When he uses the spectacles, the objects placed at infinity produce virtual iRead more
The power of the spectacles used by the myopic person, P = -1.0 D
Focal length of the spectacles, f = 1/P =1/(-1 x 10⁻² ) = —100 cm
Hence, the far point of the person is 100 cm. He might have a normal near point of 25 cm. When he uses the spectacles, the objects placed at infinity produce virtual images at 100 cm. He uses the ability of accommodation of the eye-lens to see the objects placed between 100 cm and 25 cm.
During old age, the person uses reading glasses of power, P’ = +2 D
The ability of accommodation is lost in old age. This defect is called presbyopia. As a result, he is unable to see clearly the objects placed at 25 cm.
See lessDoes short-sightedness (myopia) or long-sightedness (hypermetropia) imply necessarily that the eye has partially lost its ability of accommodation? If not, what might cause these defects of vision?
A myopic or hypermetropic person can also possess the normal ability of accommodation of the eye-lens. Myopia occurs when the eye-balls get elongated from front to back. Hypermetropia occurs when the eye-balls get shortened. When the eye- lens loses its ability of accommodation, the defect is calledRead more
A myopic or hypermetropic person can also possess the normal ability of accommodation of the eye-lens. Myopia occurs when the eye-balls get elongated from front to back. Hypermetropia occurs when the eye-balls get shortened. When the eye- lens loses its ability of accommodation, the defect is called presbyopia
See lessFor a normal eye, the far point is at infinity and the near point of distinct vision is about 25cm in front of the eye. The cornea of the eye provides a converging power of about 40 dioptres, and the least converging power of the eye-lens behind the cornea is about 20 dioptres. From this rough data estimate the range of accommodation (i.e., the range of converging power of the eye-lens) of a normal eye.
Least distance of distinct vision, d = 25 cm Far point of a normal eye, d' = ∝ Converging power of the cornea, Pc = 40 D Least converging power of the eye-lens, Pe = 20 D To see the objects at infinity, the eye uses its least converging power. Power of the eye-lens, P = Pc + Pe = 40 + 20 = 60 D PoweRead more
Least distance of distinct vision, d = 25 cm
Far point of a normal eye, d’ = ∝
Converging power of the cornea, Pc = 40 D
Least converging power of the eye-lens, Pe = 20 D
To see the objects at infinity, the eye uses its least converging power.
Power of the eye-lens, P = Pc + Pe = 40 + 20 = 60 D Power of the eye-lens is given as:
P= 1/Focal length of the eye lens (f)
f =1/P = 1/60D = 100/60 = 5/3 cm
To focus an object at the near point ,object distance (u) = -d = -25 cm
Focal length of the eye lens = Distance between the cornea and the retina = Image distance
Hence, image distance ,v = 5/3 cm
According to the lens formula ,we can write:
1/f” =1/v + 1/u
Where ,f” = focal length
1/f” = 3/5 + 1/25 = (15+1)/25 = 16/25 cm⁻¹
Power, P’ = 1/f ‘ x 100
= 16/25 x 100 = 64D
Therefor power of the eye-lens = 64-40=24D
Hence ,the range of accommodation of the eye-lens is from 20D to 24D
See lessYou are given prisms made of crown glass and flint glass with a wide variety of angles. Suggest a combination of prisms which will (a) deviate a pencil of white light without much dispersion, (b) disperse (and displace) a pencil of white light without much deviation.
(a).Place the two prisms beside each other. Make sure that their bases are on the opposite sides of the incident white light, with their faces touching each other. When the white light is incident on the first prism, it will get dispersed. When this dispersed light is incident on the second prism, iRead more
(a).Place the two prisms beside each other. Make sure that their bases are on the opposite sides of the incident white light, with their faces touching each other. When the white light is incident on the first prism, it will get dispersed. When this dispersed light is incident on the second prism, it will recombine and white light will emerge from the combination of the two prisms.
(b).Take the system of the two prisms as suggested in answer (a). Adjust (increase) the angle of the flint-glass-prism so that the deviations due to the combination of the prisms become equal. This combination will disperse the pencil of white light without much deviation.
See less