Ahair dryer has a resistance of 11.5 ω at 120 v. what is the approximate power rating of the hair dryer? 1,250 w 1,380 w 15,900 w 167,000 w

The answer is 1,250 W.  
Solution: 
To use the power rule P = VI, we need to know both the current I flowing through the resistor, and the voltage V across the resistor. But by substituting Ohm’s law I = V/R, we can also express the power rule equation P = VI as 
     P = R (V/R)^2 = R V^2 / R^2 = V^2 / R 
We can now substitute the values for the resistance and voltage into the equation to get the power rating: 
     P=V^2 / R = (120)^2 / 11.5 = 1252.17 Watts ≈ 1250 Watts 

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