A Radiometer Has Two Square Vanes (1

question 42

Multiple Choice

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 incident upon it.The other vane is blackened and it absorbs all incident radiant energy.An electromagnetic wave with an intensity of 0.30 kW/m² is incident normally upon the vanes.What is the torque due to radiation pressure on the vane assembly about the vertical axis? (c = 3.00 × 10⁸ m/s,μ₀ = 4π × 10^-7 T ∙ m/A,ε₀ = 8.85 × 10^-12 C²/N ∙ m²)

• A)2.4 × 10^-12 N ∙ m
• B)6.0 × 10^-12 N ∙ m
• C)1.2 × 10^-11 N ∙ m
• D)1.8 × 10^-11 N ∙ m
• E)2.4 × 10^-11 N ∙ m

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Definitions:

Mnemonic Devices

Tools that help people remember information through patterns such as a sequence of letters or associations.

FOIL Method

A method used in algebra to multiply two binomials, where FOIL stands for First, Outside, Inside, Last.

Binomials

Pairs of words or terms, often connected by a conjunction, that express a single idea or entity in mathematics, biology, and language.

Commutes

The act of traveling between one’s home and place of work on a regular basis, which can impact one’s work-life balance and daily schedule.