Question

The electric power consumed by a device may be calculated by the using either of the two expressions P = I2R or P = V2/R. The first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained.

Answer 1

Answer:

as v/i = r so r is directly proportional to v and inversely proportional to i.

as p = vi

that means when using i then v becomes ir thus p = i²r

whereas when using v then i becomes v/r thus v²/r.

Answer 2

Both the expressions are correct

Explanation:

Both the expressions are correct.

Case 1:

P = I²R

The current (I) remains constant.

Resistors are connected in series.

Power is directly proportional to resistance.

Case 2:

P = V²/R

The Voltage (V) remains constant.

Resistors are connected in parallel.

Power becomes inversely proportional to resistance.

So depending on whether the resistors are connected in series or parallel, the appropriate equation can be used to determine the value of power or resistance in an electric circuit.