# NCERT Class X Science Solutions: Chapter 12 – Electricity Part 4

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Question 11:

Show how you would connect three resistors, each of resistance so that the combination has a resistance of

1. To get total resistance from three resistors, we should connect two resistors in parallel and the third resistor in series with the resultant. The combination is given as follows:

Total resistance in parallel is given by

Now and are connected in series, so the net resistance is given by

1. To get total resistance from three resistors, we should connect two resistors in series and the third resistor in parallel with the resultant. The combination is given as follows:

Total resistance in series is given by

Now 𝑅12 and 6 Ω are connected in parallel, so the net resistance is given by

Question 12:

Several electric bulbs designed to be used on a electric supply line, are rated how many lamps can be connected in parallel with each other across the two wires of line if the maximum allowable current is

For one bulb:

Power and Potential difference

Using the relation for R, we have

Let the total number of bulbs be x.

Given that:

Current and Potential Difference

According to Ohm’s law,

Now, for x number of bulbs of resistance, the equivalent resistance of the resistors connected in parallel is .

Therefore, are required to draw the given amount of current.

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