A student in a town in India, where the price per unit (1unit=1kW−hr) of electricity is Rs.5.00, purchases a 1kVA UPS ( uninterrupted power supply) battery. A day before the exam 10 friends arrive at the student’s home with their laptops and all connect their laptops to the Ups. Assume that each laptop has a constant power requirement of 90W. Consider the following statements: I. All the 10 laptops can be powered by the UPS if connected directly. II. All the 10 laptops can be powered if connected using an extension box with a 3A fuse. III. If all the 10 friends use the laptop for 5hours, then the cost of the consumed electricity is about Rs.22.50.
Select the correct option with the true statements.

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I only

I and II only

I and III only

II and III only

answer is C.

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Detailed Solution

Concept- We shall first change the battery's power from kilowatt to watt. Then, we determined how many watts per second 10 computers used to consume electricity. These numbers allow us to estimate the cost of the power used concurrently by 10 laptops.
Here, the power provided by the UPS battery is equal to 1 kVA = 1000 W.
The answer to the inquiry states that the laptop uses 90W of power on a consistent basis.
Therefore, the power utilised by the 10 computers when they are all directly linked is indicated below.

P_{T} = 90 W \times 10

P_{T} = 900 W

And the 10 laptops' electricity use is,

1 kW \times 3600 \sec = 3600000 Ws

Additionally, it is stated in the question that the cost of the electricity utilised per unit is Rs. 5, hence the electricity is provided below;

1 unit = 1 kW - hr = Rs . 5.00

Consequently, the cost of the electricity used each second =

5 \times 3600

Now, if all 10 laptops were utilised simultaneously, the amount of electricity used would be as follows:

1 unit = \frac{900 \times 5 \times 3600}{3600000}

1 unit = 4.5

The cost of the electricity used by the 10 computers for 5 hours is therefore,

5 hours = 4.5 \times 5 = 22.5 rupees

A 3A bulb cannot supply the power that 10 laptops require, hence we can also state that all 10 computers can be supplied by the UPS if connected directly.
Hence, option 3 is the correct answer.

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