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Circuit Theorems and Conversions - Engineering

Q1:

A 12 V source has an internal resistance of 90 . If a load resistance of 20  is connected to the voltage source, the load power, PL, is

A 2.38 mW

B 2.38 W

C 238 mW

D 23.8 W

ANS:C - 238 mW

By voltage divider, VL = 12(20) over 20+90 = 2.18V.
P = V^2/R,
PL = (VL)(VL)/RL. *others might mistake using Rth, we are only getting PL not PT so use RL,
PL = (2.18)(2.18)/20 = 237.62 mW => 238 mW.