Final answer:
Option a, [force]/[area], has the same units as radiation pressure, since pressure is defined as the force exerted per unit area.
Step-by-step explanation:
The question asks which of the given options have the same units as radiation pressure. Radiation pressure can be understood in terms of the momentum carried by photons hitting a surface. However, the units that directly match the units of radiation pressure are found by considering the definition of pressure itself, which is force exerted per unit area.
Given the options:
- a. [force]/[area]: This equates to pressure, since force divided by area exactly defines what pressure is.
- b. [momentum]: Momentum alone, without a division by time or area, does not define pressure.
- c. [energy]/[volume]: Energy per unit volume defines energy density, not pressure.
- d. [Poynting vector]/[velocity]: The Poynting vector divided by speed could provide the dimensions of energy flux density, but not pressure directly.
Therefore, the answer is a. [force]/[area], which is the definition of pressure and has the same units as radiation pressure.