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Optics

Hot goIITian

 Joined: 20 Jul 2008 Post: 137
1 Oct 2008 19:56:48 IST
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Duration of day when there is no atmosphere on Earth? How to calculate it?
Engineering Entrance , Medical Entrance , NEET , JEE Main , AIIMS , JEE Main & Advanced , Physics , Optics

It is said that if there will be no atmosphere on Earth then the duration of the day will decrease by 4 minutes. OK, I understood that it will decrease but how to get that value (4), how to get its solution by a mathematical method?

Blazing goIITian

Joined: 8 Oct 2008
Posts: 8064
11 Oct 2008 00:05:51 IST
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hello dear,

This question can be solved by thinking in a very analytical way..

There can be two solution to this problem,the one iam giving is very accurate and the other is not logicaly correct which i can also prove as that solution have some logical flaw...

method 1

As the atmosphere rotates with the earth,if earth dont have atmosphere than moment of inertia decreases hence,omega (angular velocity) increases as angular momentum is constant....L = I W;when angular velocity incraeses than Time decrease as T = 2 * pi  / w;

method 2;

It can also be understand by the fact that the air friction ,decreases the angular velocity hence TIME increases (by obove relation) and vice versa

Note:

obove concept is wrong because atmosphere always moves with the earth,so thr is no friction between themm(air friction)...if thr is air friction than we all will burn due to it(but it doesnt hapens)

i dont think so thr is ne mathematical relation for it,as all these are calculated by taking an assumptions..

let me know ,if u need more clearification for this

Hot goIITian

Joined: 20 Jul 2008
Posts: 137
11 Oct 2008 10:51:44 IST
0 people liked this

Sir, I just wanted to know from where that value 4 came from. OK I know that time will decrease. That can also be understood by another method that as there will be no atmosphere the light will travel at its usual speed and hence time of the day will decrease. Moreover, the delayed sunset and advanced sunrise will not happen and so the duration of day will again decrease.

But, my main question is that - Is there any calculation from where this value 4 minutes came from?

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