The sky appears dark to passengers flying at very high altitudes mainly because:
Scattering of light is not enough at such heights.
There is no atmosphere at great heights.
The size of molecules is smaller than the wavelength of visible light.
The light gets scattered towards the earth.
(1)
The scattering of light takes place due to the presence of particles in the atmosphere. This is because the atmospheric medium is very rare at higher altitudes, the scattering of light that takes place at these places is very low due to which the sky appears dark to the passengers flying at very high altitudes.
Study the following ray diagram:
In this diagram, the angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by:
y, p, z
x, q, z
p, y, z
p, z, y
(3)
It is clear from the ray diagram that: The angle which is formed between the incident ray and the normal is called angle of incidence (p). The angle which is formed between emergent ray and the normal is called angle of emergence (y). The angle which is formed between the emergent ray and incident ray is called angle of deviation (z). Thus, angle of incidence, emergence and deviation is p, y and z respectively.
If a person can see a doll at the far distance, but he cannot read the newspaper in his hands. What lens should he wear to make correct his eyesight?
Convex lens
Concave lens
Bi-focal lens
Prism
(1)
If a person is unable to read a newspaper, this means the person can’t see the nearby objects. Thus, he is suffering from hypermetropia and it can be treated by using a pair of convex lenses.
The persistence of vision for the human eye is:
1/10 th of a second
1/16 th of a second
1/6 th of a second
1/10 th of a second
(2)
The persistence of vision of the human eye is 1/16 th of a second. Persistence of vision is the optical phenomenon where the illusion of motion is created because the brain interprets multiple still images as one.
The light-sensitive cell present on the retina and is sensitive to the intensity of light is:
Cones
Rods
Both rods and cones
None of these
(2)
The light-sensitive cell present on the retina and is sensitive to the intensity of light is rods.
The near point and the far point are determined with regards to the function of which part of the eye?
Pupil
Retina
Eye-ball
Ciliary muscles
(4)
The ciliary muscle also contracts and relaxes its longitudinal fibres to increase and decrease the size of the pore in the trabecular meshwork. The trabecular meshwork is responsible for aqueous humour drainage in the anterior portion of the eye.
Study the following diagram and select the option having correctly marked angles:
∠i, ∠A, ∠D
∠i, ∠r, ∠D
∠i, ∠e, ∠A
∠r, ∠e, ∠D
(1)
It is clear from the ray diagram that ∠A, ∠i and ∠D are correctly marked. ∠A represents the angle of prism which is correctly marked. ∠D represents the angle of deviation which is formed between the emergent ray and incident ray. ∠i is the angle formed by the incident ray with the normal. Thus, the correctly marked angles are ∠i, ∠A and ∠D.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power:
+0.5 D
–0.5 D
+0.2 D
–0.2 D
(2)
The lens of power –0.5 D can be used to correct the defect as:
The defect of vision in which a person cannot see the distant objects clearly but can see nearby objects clearly is called:
Myopia
Hypermetropia
Presbyopia
Bifocal eye
(1)
A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. Myopia is also known as short-sightedness.
The splitting of white light into different colours on passing through a prism is called:
Reflection
Refraction
Dispersion
Deviation
(3)
The splitting of light into its constituent colours is called dispersion. It occurs because refraction or bending differs with the colour.
