Power as energy transfer rate

Steps:

• Power is defined as the rate of doing work or transferring energy.
• Work or energy is measured in joules (J).
• Time is measured in seconds (s).
• Thus, the unit of power is J/s, or J s^{-1}.

Why D is correct:

• Power P = work/time, so the SI unit is joule per second (J s^{-1}), also called the watt.

Why the others are wrong:

• A: J C^{-1} is the unit for electric potential (volt).
• B: J m^{-1} is energy per unit length, not a power unit.
• C: N^{-1} is the inverse of force, unrelated to power.

Final answer: D