Solved: Show that the apparent brightness b ∝ AT⁴/d², where d is the distance of the... [IB Physics]

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Question

SLPaper 2

Show that the apparent brightness b ∝ AT⁴/d², where d is the distance of the object from Earth, T is the surface temperature of the object and A is the surface area of the object.

[1]

Verified

Solution

substitution of L=σAT^4 into b=L/(4πd^2) giving b=(σAT^4)/(4πd^2) 1 mark

Two of the brightest objects in the night sky seen from Earth are the planet Venus and the star Sirius. Explain why the equation b ∝ AT⁴/d² is applicable to Sirius but not to Venus.

[2]

Verified

Solution

equation applies to Sirius/stars that are luminous/emit light «from fusion» 1 mark

but Venus reflects the Sun's light/does not emit light «from fusion» 1 mark

Physics International Baccalaureate (IB) Practice Question: 1. Show that the apparent brightness b ∝ AT⁴/d², where d is the distance of the object from Earth, T is the surface temp...