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# A 150-W lightbulb emits 5% of its energy as electromagnetic radiation. What is the radiation pressure on an absorbing sphere of radius 10 m that surrounds the bulb?

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$\underline{\text{Identify the unknown:}}$

The radiation pressure on absorbing sphere

$\underline{\text{List the Knowns:}}$

Power: $P=150 \times \dfrac{5}{100}= 7.5 \;\mathrm{W}$

Distance: $r= 10 \;\mathrm{m}$

$\underline{\text{Set Up the Problem:}}$

The intensity:

$I=\dfrac{P}{4 \pi r^2}=\dfrac{7.5}{4 \pi \times (10)^2} = 5.99 \times 10^{-3} \;\mathrm{W/m^2}$

$P_{rad}=\dfrac{I}{c}$

$\underline{\text{Solve the Problem:}}$

$P_{rad}=\dfrac{5.99 \times 10^{-3}}{3 \times 10^8}=\boxed{1.997 \times 10^{-11} \;\mathrm{N/m^2}}$

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