Q27 of 44 Page 9

The distance of a galaxy is of the order of 1025 m. Calculate the order of magnitude of time taken by light to reach us from the galaxy.

Given:


Distance of galaxy from earth = 1025 m


We know that the speed of light in vacuum or space is 3 x 108 m/s.


Therefore, the time taken by light to reach earth from the galaxy can be calculated as follows




Therefore, the order of magnitude of time taken by light to reach is 1016s.


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25

(a) The earth-moon distance is about 60 earth radius. What will be the diameter of the earth (approximately in degrees) as seen from the moon?

(b) Moon is seen to be of ( �)° diameter from the earth. What must be the relative size compared to the earth?


(c) From parallax measurement, the sun is found to be at a distance of about 400 times the earth-moon distance. Estimate the ratio of sun-earth diameters.


 26

Which of the following time measuring devices is most precise?

(a) A wall clock.


(b) A stop watch.


(c) A digital watch.


(d) An atomic clock. Give reason for your answer.


 28

The Vernier scale of a travelling microscope has 50 divisions which coincide with 49 main scale divisions. If each main scale division is 0.5 mm, calculate the minimum inaccuracy in the measurement of distance.

 29

During a total solar eclipse the moon almost entirely covers the sphere of the sun. Write the relation between the distances and sizes of the sun and moon.