A radiometer has two square vanes (1.0 cm by 1.0 cm), attached to a light horizo

Question

A radiometer has two square vanes (1.0 cm by 1.0 cm), attached to a light horizontal cross arm, and pivoted about a vertical axis through the center, as shown in the figure. The center of each vane is 6.0 cm from the axis. One vane is silvered and it reflects all radiant energy that falls upon it. The other vane is blackened and it absorbs all incident radiant energy. Radiant energy, having an average intensity of 300 W/m2, is incident normally upon the front surfaces of both vanes. What is the radiant power absorbed by the blackened vane?

A) 0.040 W

B) 0.090 W

C) 0.030 W

D) 0.060 W

E) 0.050 W

Really need explaination...

Explanation / Answer

The radiant energy absorbed can be given by

Eab = I X A

where I is the intensity and A is the area.

Eab = 300(0.01m)2 = 0.03 W = 0.03 J/s :-)

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