Q. 22

The energy from the sun reaches just outside the earth’s atmosphere at a rate of 1400 W m–2. The distance between the sun and the earth is 1.5 × 1011 m.

(a) Calculate the rate at which the sun is losing its mass.

(b) How long will the sun last assuming a constant decay at this rate? The present mass of the sun is 2 × 1030 kg.

Answer :


The amount of energy radiated by the sun in

As the energy radiated is dependent on the surface area it covers which is given by

Energy loosed by the sun till it reaches earth in 1 second is given by

So, the mass loosed by the sun in 1 second is


As the rate of decay of the mass is constant it will last up to

In years

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