NCERT Class X Science Solutions: Chapter 12 – Electricity Part 5

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Question 13:

A hot plate of an electric oven connected to a line has two resistance coils A and B, each of resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?

Answer:

Given that:

Potential difference and resistance of each coil

When the coil is used separately, the current in the coil is given by

When the two coils are connected in series, the net resistance is given by

Now, the current in the coil is given by

Image result for two resistance are connected in series

Two Resistance Are Connected in Series

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When the two coils are connected in parallel, the net resistance is given by

Now, the current in the coil is given by

Result for two coils are connected in parallel

Two Coils Are Connected in Parallel

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Question 14:

Compare the power used in the resistor in each of the following circuits:

  1. A battery in series with and resistors.

  2. A battery in parallel with and resistors.

Answer:

Given that:

Potential difference,

  1. and resistors are connected in series. Therefore, equivalent resistance of the circuit,

According to Ohm’s law,

V = IR

In series combination, the current in the circuit remains constant. Therefore power is given by

  1. and resistors are connected in parallel.

In parallel combination, the voltage in the circuit remains constant. Therefore power is given by

Hence, in both the cases power remains same as 8W.

Question 15:

Two lamps, one rated and the other, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is

Answer:

For the lamp one:

Power and Potential difference

Therefore,

For the lamp two:

Power and Potential difference V

Therefore,

So, the net current drawn from the supply is given by