1.

It takes 5 years for light to reach the earth from a star. Express the distance of star from the earth in (i) light year, (ii) km . Take speed of light = 3xx10^8 m s^(-1) and1 year = 3.153 xx 10^7 s

Answer»

Solution :The distance travelled by LIGHT in 1 YEAR is called 1 light year. Thus the distance travelled by light in 5 years = 5 light year.
`THEREFORE` Distance of star from the earth = 5 light year.
(ii) 1 light year = speed of light `xx` TIME `1 ` year
`=(3xx 10^8 m s^(-1)) xx (3.153xx10^(12)s)`
`= (9.46xx10^(15) m = 9.46xx10^(12) km `
`therefore ` Distance of star from the earth `= 5 xx 9.46 xx 10^(12)` km
`= 4.73xx10^(13) km `


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