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ICSE Class 10 Physics Solved Question Paper 2005

Short Answer Type

Which physical quantity does this electronvolt measure? How is it related to the S.I. unit of this quantity?

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What should be the angle between force and displacement be to get the

i) minimum work

ii) maximum work?

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State Newton’s Second Law of motion.

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The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one minute.

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Mention two properties of a wave: one property which varies and the other which remains constant when the wave passes from one medium to another.

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6.
Explain briefly what causes the twinkling of stars at night?

The atmosphere can be considered to consists of a number of parallel layers of air of different densities and therefore of different refractive indices. The density and the refractive index of the layers decrease with altitude. As the light from the stars enters the earth’s atmosphere it undergoes refraction and bends towards the normal. As a result to an observer on the Earth, the star appears to be higher in the sky than it’s actual position. Owing to the constant changes the the density of different layers of air due to convection current or motion of the earth’s atmosphere, the refractive index of the layers also changes. Thus, the apparent positions of the stars appear to be changing. This also reduces or increases the intensity of the light from the stars. Hence, the stars appear sometimes brighter and sometimes dimmer. The light coming the stars, therefore, presents a quivering (shaking ) appearance thus giving the impression as if the stars are twinkling.

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