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7. Sum of Electrical Power Electrical Energy Consumed by a Resistive Load

Three sums of electrical power have been discussed in this video. This is the second part of sum discussion .

Sum 1: A water heater has a rating of 4 KVA , 240 V.
a) What is the electrical energy consumed by it in:
i)KWhr and
ii) in Joul.
if it is used for 180 minutes.
b) Find the cost of electricity if the rate is
Rs. 7.00 per commercial unit.

Sum 2: The water in an electric kettle took 5 minutes to reach its boiling point when it is connected to 220 v supply.
How long would it have taken if the supply voltage had fallen to 200 v.

Sum 3: What is the resistance under normal working conditions of 240V electric lamp rated at 60 W ? If two such lamps are connected in series across a 240 mains supply, explain why each one appears less bright.

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