Because metal expand with heat in summer higher the temperature more the wire will expand in winter's the wires get tight that is the reason you think that wires expand in summers.

The correct answer is option 'C', which states that the wires expand on heating. This phenomenon occurs because of the properties of metal, which exhibit thermal expansion.

**Thermal Expansion of Metals:**

Metals are known to expand when heated and contract when cooled. This behavior is a result of their atomic structure and the movement of the atoms within the metal lattice. When the temperature of a metal increases, the atoms vibrate more vigorously, causing an increase in the average distance between them. As a result, the metal expands and occupies a larger volume.

**Effects of Thermal Expansion on Wires:**

In the case of electric wires or telephone wires, which are typically made of metal such as copper or aluminum, thermal expansion plays a significant role. During winter, when the ambient temperature is low, the wires contract due to the decrease in temperature. This contraction causes the wires to become tight and appear more taut.

Conversely, during summer when the temperature rises, the wires are subjected to increased heat. As a result, the metal wires expand due to thermal expansion. This expansion causes the wires to sag slightly, as they occupy a larger volume. The sagging of the wires can be observed as a slight drooping or bending.

**Reason for Sagging:**

The sagging of wires during summer is a consequence of the expansion of the metal. As the wires expand, they exert an outward force on the supports or poles to which they are attached. This force causes the wires to sag downwards, as they are not rigid enough to resist the expansion.

It is important to note that the extent of sagging depends on various factors such as the length and thickness of the wire, the material of the wire, and the temperature difference between winter and summer. Wires with greater lengths and thinner diameters will exhibit more sagging compared to shorter and thicker wires.

In conclusion, electric wires or telephone wires become tight during winter and sag a little during summers because metal wires expand when heated. This expansion is a result of the thermal expansion properties of metals, causing the wires to occupy a larger volume and exerting an outward force that leads to sagging.

Electric wires are made of metals. Also we know that metals expand on heating.