A Radiometer Has Two Square Vanes (Each Measuring 1

question 2

Multiple Choice

A radiometer has two square vanes (each measuring 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 electromagnetic power absorbed by the blackened vane? (c = 3.00 × 10⁸ m/s, μ₀ = 4π × 10^-7 T ∙ m/A, ε₀ = 8.85 × 10^-12 C²/N ∙ m²)

• A) 0.030 W
• B) 0.040 W
• C) 0.050 W
• D) 0.060 W
• E) 0.090 W

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Definitions:

Transcription Factor

Regulatory protein that influences transcription by binding directly to DNA; e.g., an activator or repressor.

Enhancer

DNA sequences that increase the transcription level of a gene they are associated with, enhancing gene expression.

Lactose Operon

A group of genes involved in the metabolism of lactose in bacteria, controlled by a mechanism that turns gene expression on or off depending on the presence of lactose.

Enzymes

Biological molecules, typically proteins, that significantly speed up the rate of virtually all of the chemical reactions that take place within cells.