Understanding the Unit of Power: Watt

The question asks us to identify the correct definition for the unit of power, which is the Watt (W).

Defining Power

In physics, power is defined as the rate at which work is done or energy is transferred. It essentially measures how quickly energy is used or converted from one form to another.

The standard formula relating power ($P$), energy ($E$), and time ($t$) is:

$ P = \frac{E}{t} $

Here:

• $P$ represents Power, measured in Watts (W).
• $E$ represents Energy, measured in Joules (J).
• $t$ represents Time, measured in seconds (s).

Therefore, based on this definition, 1 Watt is equivalent to 1 Joule of energy transferred or work done per second.

Analyzing the Options

Let's examine each option provided:

• Option 1: $1$ ohm / $1$ second
  The unit 'ohm' ($\Omega$) measures electrical resistance, not energy or power. Dividing resistance by time does not yield power.
• Option 2: $1$ coulomb / $1$ second
  The unit 'coulomb' (C) measures electric charge. The rate of charge flow (charge per second) is defined as electric current, measured in Amperes (A). So, $1 \text{ C} / 1 \text{ s} = 1 \text{ A}$. This is not power.
• Option 3: $1$ ampere / $1$ second
  The unit 'ampere' (A) measures electric current. Dividing current by time does not define power.
• Option 4: $1$ joule / $1$ second
  The unit 'joule' (J) measures energy. As explained above, energy divided by time ($J/s$) is the definition of power. Thus, $1 \text{ J} / 1 \text{ s} = 1 \text{ W}$. This option correctly defines the Watt.

Conclusion

Based on the fundamental definition of power in physics, the unit Watt (W) is defined as the rate of energy transfer, specifically 1 Joule of energy per 1 second.