An 800-KHz Radio Signal Is Detected at a Point 8

question 14

Multiple Choice

An 800-kHz radio signal is detected at a point 8.5 km distant from a transmitter tower.The electric field amplitude of the signal at that point is 0.90 V/m.Assume that the signal power is radiated uniformly in all directions and that radio waves incident upon the ground are completely absorbed.What is the average electromagnetic energy density at that point? (c = 3.0 × 10⁸ m/s,μ₀ = 4π × 10^-7 T ∙ m/A,ε₀ = 8.85 × 10^-12 C²/N ∙ m²)

• A)3.6 pJ/m³
• B)5.1 pJ/m³
• C)7.2 pJ/m³
• D)10 pJ/m³
• E)14 pJ/m³

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Definitions:

Biogeochemical Cycle

The recycling of inorganic matter between living organisms and their environment, involving processes such as the carbon cycle and nitrogen cycle.

Fossil Fuels

Non-renewable energy sources formed from the remnants of ancient plants and animals, including coal, oil, and natural gas.

Biogeochemical Cycles

Processes that recycle essential elements and compounds between the biological (living) and geochemical (non-living) components of the Earth.

Stable Ecosystems

Ecosystems that remain relatively constant in terms of their species composition, structure, and function despite disturbances.