5) A 1500 W electric hair dryer is designed to work in the United States, where

Question

5) A 1500 W electric hair dryer is designed to work in the United States, where the AC voltage is 120 V rms. What power is dissipated in the hair dryer when it is plugged into a 240 V rms socket in Europe ?


10) A hair dryer has a power rating of 1200 W at 120 V rms. Assume the hair dryer circuit contains only resistance.

a) What is the resistance of the heating element ?

b) What is the rms current drawn by the hair dryer ?

c) What is the maximum instantaneous power that the resistance must withstand ?

Explanation / Answer

5)The power consumed by the electric hair dryer is P = 1500 W The AC voltage is Vrms = 120 V
Let the power consumed in the hair dryer when it is plugged to a Vrms1 = 240 V socket in Europe be P1 We know from the relation P = Vrms * Irms or Irms = (P/Vrms) Similarly, P1 = Vrms1 * Irms = Vrms1 * (P/Vrms) 10)The hair dryer has a power rating of P = 1200 W at V = 120 V rms a)Let the resistance of the heating element be R We know that P = V * I where I = (V/R) or P = V * (V/R) = (V2/R) or R = (V2/P) b)The rms current drawn by the hair dryer is I = (P/V) c)The maximum instantaneous power that the resistance must withstand is Pmax = (Vmax2/R)
where Vmax = v2 * Vrms = 1.414 * 120 = 169.7 V

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