a) At the earth's surface, the radiant power received from the Sun normally is 1.3×103 W per square metre. The power radiated by the Sun is the same everywhere over the Sun's surface. If the Earth orbits at a distance of 1.5×1011 m from the Sun, calculate the total energy radiated away by the Sun each second. (It may be useful to know that the surface area of a sphere is 4πr2). [2]
b) Although you may not have studied it yet, Einstein produced a famous equation relating mass and energy which we shall use, E=mc2, where E is energy in joules, m is mass in kg, c is the velocity of light in a vacuum (c=3×108 m/s). Using your answer to part (a), calculate the mass loss of the Sun due to the energy being radiated away each second. [1]
c) If the mass of the Sun is 2×1030 kg, what is the percentage of the Sun's mass that is lost by radiation each year? [2]
d) Assuming that this rate remains constant, what is the percentage loss of mass of the sun since it was formed, five thousand million years ago? [2]