# Class 11 Physics Unit & measurment: NCERT Solutions for Question 31

This page focuses on the detailed Unit & measurment question answers for Class 11 Physics Unit & measurment, addressing the question: 'The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?'. The solution provides a thorough breakdown of the question, highlighting key concepts and approaches to arrive at the correct answer. This easy-to-understand explanation will help students develop better problem-solving skills, reinforcing their understanding of the chapter and aiding in exam preparation.
Question 31

## The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?

Time taken by quasar light to reach Earth = 3 billion years

= 3 x 109 years

= 3 x 109 x 365 x 24 x 60 x 60 s

Speed of light = 3 x 108 m/s

Distance between the Earth and quasar

= (3 x 108) x (3 x 109 x 365 x 24 x 60 x 60)

= 283824 x 1020 m

= 2.8 x 1022 km