A super nova releases 1.2×10 45 J of energy. It is1540 ly from earth. If you wer

Question

A super nova releases 1.2×1045 J of energy. It is1540 ly from earth. If you were facing the star in question, andyour face was a circle 7 cm in radius, how much energy would reachyour face?

Hint: Don't get hung up searching for formulas.Think: If your face was a gigantic hemisphere (bowl-shaped)centered on the nova, then you would intercept half the energy fromthe nova. If your face was a 1/8 sphere centered on the nova, youwould catch 1/8 the energy. What fraction of the sphere is yourface really? You may be worried that the amount of energy receivedby the face is so large as to be fatal. The energy from a supernovais released over a several-week period, so the large energyabsorbed by the face is absorbed slowly over a long time.

Explanation / Answer

intensity of light from supernova I1= (P1/A1) intensity of light falling on face I2 = (P2/A2) I1 = I2 or (P1/A1) = (P2/A2) or (E1/A1) = (E2/A2) or (E1/4r^2) = (E2/4r1^2) or E2 = E1 * (r1/r)^2 E1= 1.2×1045 J r1= 7 cm = 7 * 10^-2 m and r = 1540 ly = 1540 * 9.46 * 10^15 m substitute the values

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