Question

17. Which of the following is the correct formula for finding power in a DC circuit? A. P = I2R B. P = VR C. P = IR D. P = V2I

Answer 1

Choice-A is one of several useful, correct formulas for electrical power. It's true in AC circuits as well as DC ones.

Answer 2

Choice A. P = I² · R where

• P is the power in the DC circuit,
• I is the current through the circuit, and
• R is the total resistance of the circuit.

Explanation:

Electrical power is the rate at which the electrical force does work. So what is electrical work? That's the work
`W` that the electrical force do when it moves charges
`Q` across a potential difference
`V`:

W =
`V\cdot Q`.

The power is the rate at which the electrical force do the work:

`\displaystyle P = (W)/(t) = V \cdot (Q)/(t)`.

On the other hand, current
`I` is the charge through a cross-section of the circuit in unit time. By the definition of current:

`\displaystyle(Q)/(t) = I`.

`\displaystyle P =V \cdot (Q)/(t) = V\cdot I`.

Consider Ohm's Law:

`V = I \cdot R`.

Therefore

`\displaystyle P = V\cdot I = (I \cdot R) \cdot I = I^(2)\cdot R`.