Question

(a) Define the power of accommodation. What is its value for a young adult with
normal vision?
(b) Why do stars twinkle?

{ANSWER WITH EXPLANATION}

{ALIGARH MUSLIM UNIVERSITY BOARD OF SECONDARY AND SENIOR SECONDARY EDUCATION, SAMPLE PAPER}

Answer 1

Heya brother!!
Here's your answer:

(a) Power of accommodation is the ability of mammalian eye to adjust the convexity of the eye lens to view objects at different distances distinctly.
For this ability, you can view a book (kept right in front of you) and a star (at infinity), both clearly.
To view near objects, your lens becomes more convex, while for viewing distant objects, your lens becomes flat (less convex). The ciliary muscles and the suspensory ligaments are the accommodating apparatus, I.e., they are responsible for changing the convexity of the lens.

(b) Stars are luminous bodies located closer to the earth. As the light rays from stars reach us, they suffer multiple refractions at the layers of the atmosphere, at after each successive refraction, it bends towards the normal (since the upper layers are rarer than the lower).

Now, what happens is that, the density of the layers continuously changes, due to slight change in temperature and pressure (and other conditions), due to which the apparent position of the stars continuously changes (I.e., it seems to move from its position slightly each time), hence, it appears twinkling.

Thanks!!

Answer 2

HEYA!!!!!

ACCOMMODATION : The ability to adjust the focal length is known as Accommodation of the lens.

The power of accommodation :

☆ The ciliary muscles relax when if Want to see the far distance objects.

☆ It Contracts when we Want to see near objects.

☆ When the ciliary muscles relax the focal length increase and we can see the far objects clearly.

☆ When the ciliary muscles contract then the focal length decrease and we can see near objects clearly.


Q.2 : Why do stars twinkle ?

A: Stars do not twinkle they just appear to twinkle when seen from the surface of Earth. The stars twinkle in the night sky because of the effects of our atmosphere. When starlight enters our atmosphere it is affected by winds in the atmosphere and by areas with different temperatures and densities. Then the light of stars passes from different mediums.So, they appear as twinkle...


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