Question

A lamp and a coffee maker are connected in parallel to the same 120-V source. Together, they use a total of 140 W of power. The resistance of the coffee maker is 300 Ohm. Find the resistance of the lamp.

Answer 1

Resistance of the lamp (r) = 156.52 ohm (Approx.)

Step-by-step explanation:

Given:

Total power p = 140 W

Resistance of the coffee maker = 300 Ohm

Voltage v = 120 V

Find:

Resistance of the lamp (r)

Computation:

We know that

p = v² / R

SO,

Total power p = [Voltage²/Resistance of the lamp (r)] + [Voltage²/Resistance of the coffee maker]

140 = [120² / r] + [120²/300]

140 = 120²[1/r + 1/300]

140 = 14,400 [1/r + 1/300]

Resistance of the lamp (r) = 156.52 ohm (Approx.)