Electricity in a city is billed in two slabs: the first units (kWh) in a month are…

PHYSICS · Multi-part · CBSE · Physics · Current Electricity · Current Electricity

Problem

Electricity in a city is billed in two slabs: the first

200

units (kWh) in a month are charged at Rs

5

per unit, and any consumption beyond that is charged at Rs

8

per unit. A household uses the appliances listed below. • Refrigerator of

300\,\text{W}

working effectively for

16\,\text{h}

per day. • Washing machine of

500\,\text{W}

used for

1\,\text{h}

per day. • Mixer-grinder of

400\,\text{W}

used for

15\,\text{min}

per day. • Fifteen LED bulbs of

9\,\text{W}

each, switched on for

5\,\text{h}

per day. • Three ceiling fans of

70\,\text{W}

each, running for

8\,\text{h}

per day. (i) Calculate the total electrical energy consumed by the household in one day and in a

30

-day month. (ii) Compute the monthly electricity bill according to the given slab rates. (iii) The family wants to limit the monthly bill to Rs

1200

by reducing the daily operating time of all three fans equally, while the usage of other appliances remains unchanged. Find the new number of hours per day for which each fan should run so that the total monthly bill does not exceed Rs

1200

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