IB Physics HL B.1 practice question

Question 1

Paper 2Easy7 marks

A student models the apparent brightness $b$ of a star at different distances $d$ assuming the star’s luminosity $L$ remains constant. The relationship is

b=\frac{L}{4\pi d^2}

where $b$ is measured in $\mathrm{W\,m^{-2}}$ $L$ in $\mathrm{W}$ and $d$ in $\mathrm{m}$

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

(a)

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

[1]

(b)

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

[3]

(c)

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

[1]

(d)

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

[2]

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