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Two bulbs of $40 W$ each are lighted for eight hours daily. Find the cost of electrical energy consumed by them in one week at Rs. $3$ per unit.

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Rs 13.44

Rs 13

Rs 14

Rs 20

answer is A.

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Detailed Solution

The cost of electrical energy consumed by them in one week at Rs.

3

per unit is

Rs 13.44 .

In general, power is given by

\Rightarrow P = \frac{E}{t}

Where

E

is the energy and

t

is the time.
Power of device

P = 40 W

Time

t = 8 hr

Therefore,

\Rightarrow P = \frac{E}{t}

\Rightarrow E = P \times t

\Rightarrow E = 40 \times 8

\Rightarrow E = 320 J

Energy consumed by

2

bulbs in

1

week,

\Rightarrow E = 320 \times 2 \times 7

\Rightarrow E = 4.48 kW

Therefore total power consumed is

4.48 units

.
Hence, the total cost

= 4.48 \times 3

= Rs 13.44 .

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