IB Physics HL B.1 Thermal energy transfers questions

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Question 1

Paper 2Easy7 marks

A student models the apparent brightness bb of a star at different distances dd assuming the star’s luminosity LL remains constant. The relationship is

b=L4πd2b=\frac{L}{4\pi d^2}

where bb is measured in W m−2\mathrm{W\,m^{-2}} LL in W\mathrm{W} and dd in m\mathrm{m}

Figure 1 shows the modelled apparent brightness as the distance from the star is changed.

00.511.522.533.5400.511.522.5d / (1016 m)b / (10-5 W m-2)
(a)

Use Figure 1 to determine the apparent brightness of the star when d=1.0×1016 md=1.0\times10^{16}\,\mathrm{m}

[1]
(b)

Using your answer to (a), calculate the luminosity of the star.

[3]
(c)

Use Figure 1 to determine the apparent brightness when d=2.0×1016 md=2.0\times10^{16}\,\mathrm{m}

[1]
(d)

State the factor by which the apparent brightness changes when the distance increases from 1.0×1016 m1.0\times10^{16}\,\mathrm{m} to 2.0×1016 m2.0\times10^{16}\,\mathrm{m} and explain this change using the relationship given.

[2]

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