How to find the wattage of the 20 Ω load?

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adamaero

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Electrical Engineer
A 20 Ω and 4 Ω resistor are in series. The voltage across the 4 Ω load is 24 V.
What is the wattage of the 20 Ω load?

1674224935841.png

a) 120 W
b) 48 W
c) 144 W
d) 720 W

P = IV = V^2/R
 
230120-0947 EST

adamaero:

You obviously know the answer. But why draw the circuit as shown? You show no voltage source. So I will assume it is inductively coupled into your 1 turn loop. Now, if this is intended to be a trick question, then I don't know what the object is because you only supply 4 answers.

It is a simple question to answer. So what is the real purpose of the question as presented.

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The simple-math approach:

The 20-ohm resistor is five times the 4, so its voltage drop will be (5 x 24) 120v.

E = I x R, so you need the current. 24 + 120 = 144, the circuit voltage, 4 + 20 = 24, the resistance.

I = E/R = 144 / 24 = 6a. E = I x R = 6 x 20 = 120v. P = E x I = 120 x 6 = 720w.
 
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