Practice!

Sample Problem

What is the power of the 40 Ω resistor in the circuit? W. (Round to the nearest tenth) .

Solution

P = VI = I2R

I = Vt/Rt

Rt = 40 Ω + Requivalent

Requivalent = 1 ÷ (1/20 + 1/ 5 + 1/ 10) = 2.86 Ω

Rt = 40 Ω + 2.86 Ω = 42.86 Ω

I = Vt/Rt = 120 V ÷42.86 Ω = 2.80 A

P = 313.6 W