A typical hairdryer has some sort of power rating on the box

A typical hairdryer has some sort of power rating on the box.

(a) How much current will the hairdryer draw if it’s rated for 1000W and used in the U.S.?

(b) What kind of resistor (what is the resistance) does this hairdryer use?

(c) Estimate how long you need to dry your hair using this hairdryer (assume water’s enthalpy of evaporation is 2200 KJ/kg, and assume there is 100g of water in your hair). You don’t need a new formula, look at the unit and solve for the right properties.

Solution

Power P = 1000 W

Voltage V = 120 volt

Since Electrical sockets (outlets) in the United States of America usually supply electricity at between 110 and 120 volts.

Here i take 120 volts

(a). Current i = P / V

                   = 1000 /120

                   = 8.333 A

(b).Resistance R = V / i

                         = 14.4 ohm

(c).Mass of water m = 100 g = 0.1 kg

water’s enthalpy of evaporation L = 2200 KJ/kg

Energy E = mL

              = 220 kJ

             = 220x10 ³ J

Required time t = E / P

                       =(220x10 ³) /1000

                      = 220 s

                      = (220/60) min

                      = 3.666 min