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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. |