Explanation
Correct answer is (b)
Spectrum of visible light runs from violet to red, which is banded on either side by ultraviolet and infrared rays.
The deviation of light is inversely proportional to the wavelength. Since, red light has the longest wavelength among the seven colours with about 650 nm. Hence its deviation is the least among all colours.
Correct answer (a)
The eyeball is approximately spherical in shape with a diameter of about 2.3 cm.
Correct answer is (c).
Long-sightedness, affects a person's ability to see objects close to them, these vision problems are also referred to as refractive errors. A person having long-sighted eye, usually is able to see distant objects clearly, but nearby objects will be out of focus, and as the man cannot see the objects distinctly at a distance less than 1 meter so he is suffering from Long-sightedness.
Power of Accommodation is the ability of the eye lens to adjust its focal length. The ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina.
When the muscles are relaxed, the lens becomes thin. Its focal length increases. This enables us to see distant objects clearly.
To look at objects closer to the eye, the ciliary muscles contract. The eye lens then becomes thicker. The focal length of the eye lens decreases. This enables us to see nearby objects clearly.
If a person cannot see an object clearly when it is placed at about 25 cm away from him, he is suffering from:
The power of accommodation of the eye usually decreases with ageing. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia. It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens.
Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bi-focal lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision.
The blue colour of the sky is due to the scattering of light by small particles of the atmosphere (air molecules). When white light (from the sun) enters the earth's atmosphere, it gets scattered away due to the atmospheric particles. Since blue colour has the minimum wavelength, so blue colour scatters the most and thus the sky appears blue.
$$Answer:-$$ C option
In the problem, it is given that the near point of defective eye is 1 m and that of a normal eye is 25 cm. Hence $$u = -25$$ cm. The lens used forms its virtual image at near point of hypermetropic eye i.e., $$v = - 1 m = -100$$ cm.
Using lens formula, we have :-
$$\dfrac { 1 }{ v } -\dfrac { 1 }{ u } =\dfrac { 1 }{ f } \\ \dfrac { 1 }{ -100 } -\dfrac { 1 }{ -25 } =\dfrac { 1 }{ f } \\ f=\dfrac { 100 }{ 3 } =0.33\quad m\\ power=\dfrac { 1 }{ f(in\quad metres) } =+3.0\quad D$$
Please disable the adBlock and continue. Thank you.
