![]() However, even the nearest stars are so distant that with such a long baseline, they show parallax only of the order of 1” (second) of arc or so. That is, the baseline is about the diameter of the Earth’s orbit ≈ 3 × 1011m. The baseline AB is the line joining the Earth’s two locations six months apart in its orbit around the Sun. 2.19 The principle of ‘parallax’ in section 2.3.1 is used in the determination of distances of very distant stars. (In fact, since you are aware that you are moving, these distant objects seem to move with you). seem to move rapidly in a direction opposite to the train’s motion, but the distant objects (hill tops, the Moon, the stars etc.) seem to be stationary. Why is this ratio so large ? 2.18 Explain this common observation clearly : If you look out of the window of a fast moving train, the nearby trees, houses etc. What is the ratio of molar volume to the atomic volume of a mole of hydrogen ? (Take the size of hydrogen molecule to be about 1 Å). What is the total atomic volume in m3 of a mole of hydrogen atoms ? 2.17 One mole of an ideal gas at standard temperature and pressure occupies 22.4 L (molar volume). The size of a hydrogen atom is about 0.5 Å. 2.16 The unit of length convenient on the atomic scale is known as an angstrom and is denoted by Å: 1 Å = 10–10 m. A boy recalls the relation almost correctly but forgets where to put the constant c. (This relation first arose as a consequence of special relativity due to Albert Einstein). 2.15 A famous relation in physics relates ‘moving mass’ m to the ‘rest mass’ mo of a particle in terms of its speed v and the speed of light, c. Rule out the wrong formulas on dimensional grounds. Cos 2πt / T ) (a = maximum displacement of the particle, v = speed of the particle. ![]()
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