# NCERT Class X Science Solutions: Chapter 12 – Electricity Part 2

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**Question 4:**

Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be

**Answer: C**

Heat produced in the circuit is inversely proportional to the resistance R. Let and be the equivalent resistances of the wires if connected in series and parallel respectively. Let R be the resistance of each wire.

If the resistors are connected in parallel, the net resistance is given by

If the resistors are connected in series, the net resistance is given by

Hence, for same potential difference V, the ratio of heat produced in the circuit is given by

Therefore, the ratio of heat produced in series and parallel combinations is

Hence, the option **C** is correct.

**Question 5:**

How is a voltmeter connected in the circuit to measure the potential difference between two points?

**Answer:**

To measure the potential difference, a voltmeter should be connected in parallel.

A voltmeter is a device that measures potential difference.

The voltmeter must be connected in parallel with the elements being measured.

**Question 6:**

A copper wire has diameter and resistivity of what will be the length of this wire to make its resistance how much does the resistance change if the diameter is doubled?

**Answer:**

Resistance of a copper wire of length and cross-section is given by the expression,

Where, 𝜌 is resistivity of copper

Radius of wire

If the diameter (radius) is doubled, the new radius

So, the new resistance will be

Now

Hence, the new resistance will become ¼ times the original resistance.