A 75 Watt water tank heater designed to be used with an rms voltage of 120 V is

Question

A 75 Watt water tank heater designed to be used with an rms voltage of 120 V is brought to an isolated research station where the rms voltage is 220 V. (1) what is the resistance of the heating element? (2) If the heater is plugged into a 220 V outlet, what rms and maximum currents will the heater try to draw from the outlet? What average power will the heater dissipate (unless something bad already happens at a current less than the values found above)? (3) In order to use the heater safely, you decide to improvise a transformer from some materials available locally. You have enough wire for no more than 20 total windings around and old transformer core. How many windings should you warp an the input side and the output side of your transformer if you want to step the output voltage down to 120 Vrms ? (4) what rms and maximum current will the input side of the transformer draw from the outlet?

Explanation / Answer

1)We know that power=V2/R

R=2202/75=645.33 ohm

2)Voltage=220 V

current=V/R=220/645.33=0.34 A

Power=I*V=0.34*220=75 watts

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