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An electric gryster is known to consume 2.2 units of electrical energy per hour of its use.It is designed to work on the main voltage of 220v.What is the current flowing through the device?When it is across the main, what is the resistance of the device?Which of the two a 100w.220v lamp or 10w.220v night bulb has high reisitance?

 

Kwh = 2.2 units, V = 220V, current =?, Resistance =?, current = wattage/voltage =

Power consumption Kwh = watts ×hours used × days used ÷ 1000

 

i.e.,2.2 units = power in watts × 2hrs/1000

 

power in watts = 2.2 × 1000 /2  = 1.1 × 1000 = 1100 W

I = P /E

i.e., Current = power in watts /voltage

 

              = 1100/220 = 5 A

i.e., The current flowing through the device = 5 amps

Resistance = E/I = 220 V/ 5 A = 44 ohm 

 

i.e., When 5 amps current is across the main, the resistance of the device = 44 ohm 

 

When 100W. 220 V lamp is used, Resistance = E2 /P = (220V)2 / 100W =  484 ohm 

 

When 10W. 220 V night bulb is used, Resistance = E2 /P = (220V)2 / 10W = 4840 ohms

 

i.e.,10W. 220V night bulb has high resistance.



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