Would you mind explaining the calculation behind Q13 and Q15?
We’ve been given the equation for the power that is used for cooling and if we plug in the values we get 15 (26 – 6). To work out the power used, just divide by the efficiency which is 30%. This is the same as multiplying by 100 / 30. So you get 15 x 20 x 100 / 30.
Power of light from a star obeys a 1/r² law. The brighter star is twice as far away so its power must be reduced by a factor of 4 when it reaches the eye. So if it looks to have the same brighness it must be emitting 4 times the power.
Thank you in advance
It’s a pleasure.
Thank you for this great site!
Can you please clarify why the period is proportional to the sqrt of r^3?
It is Kepler’s Third Law. You can see a brief explanation of how to derive it here.
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