Question

An electric geyser is known to consume 2.2 'units ' of electrical energy per hour of its use it is designed to work on then voltage of 220v. 1 what is the power-rating of this device 2 what is the current flowing through this device when it is connected across the mains 3what is the resistance of this device does the resistance of this device remain constant during its operation/working which of the two- a100w, 220v lamp or a 10w, 220v night lamp - has a higherresistance

Answer 1

Geyser is rated for 2.2 kW or 2200 W.

current is 2200/220=10 A Resistance of heater coil=220/10=22 ohmThe resistance varies as the coil gets heated up

Resistance of 100 W bulb = R100 =220 x 220/100= 484 ohm

Resistance of 10 W bulb = R10 =220 x 220/10= 4840 ohm

3. So resistance of 10 W bulb is more.

Answer 2

V = 220 V                     E = 2.2 KWH     as 1 unit = 1 KWH

Power = Energy/Time = 2.2 KWH / 1 hr  =2.2 KW

I = P / V = 2.2 KW / 220V = 10 A

R = V / I = 22 Ω

==========================

Power P = V²/R    => R = V² / P

100W ,220V  lamp  =>  R = 220²/100  Ohms

10 W , 220V  night lamp =>  R = 220²/10  ohms

So  the night lamp has higher resistance.

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