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?

Solution

We have here,
Time taken by quasar light to reach Earth = 3 billion years
$straight t space equals space 3.0 space cross times space 10 to the power of 9 space years space space space equals 3.0 space cross times space 10 to the power of 9 space cross times 365 cross times 24 cross times 60 cross times 60 space straight s space space equals space 9.46 space cross times space 10 to the power of 16 space straight s space Speed space of space light space equals space 3 space cross times space 10 to the power of 8 space straight m divided by straight s Distance space between space Earth space and space quasar space is comma space equals space left parenthesis 3 space cross times space 10 to the power of 8 right parenthesis space cross times space 9.46 space cross times space 10 to the power of 16 space straight s space equals space 283824 space cross times space 1020 space straight m space equals space 2.8 space cross times space 10 to the power of 22 space km$

Some More Questions From Units and Measurement Chapter

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Units And Measurement

Some More Questions From Units and Measurement Chapter

Define physical quantity.

Give four examples of physical quantities.

Define unit.

What are the two main required characteristics of a unit?

Can we use same units for different physical quantities?

Can we use different units to measure same physical quantity?

To measure a physical quantity X, the unit U is repeatedly used for n times. What is the magnitude of physical quantity?

Does the numerical factor in the quantitative measurement depend on the system of unit used?

Is one unit sufficient to measure a physical quantity?

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