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Question: There is a hole in the middle of a copper plate, when heating the plate, the diameter of the hole wo...

There is a hole in the middle of a copper plate, when heating the plate, the diameter of the hole would: A) always increase B) always decrease C) remains the same D) none of these

Explanation

Solution

When there is a fixed temperature, two atoms, of a crystalline solid, maintain an average distance between them and vibrate. This average distance increases with the rise in temperature.

Complete step by step solution:
Usually all solid substances expand on heating and contract on cooling. For a certain rise in temperature, this change is so small for solids, compared to that of liquids and gases, that the change is not always noticeable. But, with the help of proper experiments, it can be shown that solids expand on heating. This phenomenon of expansion with the change in temperature is called thermal expansion.

So, as metal is a solid it expands on heating. So, if there is a hole in the middle of a copper plate, the hole will also increase due to the expansion of the metal. The reason behind it is that the air in the region of the hole will also increase due to heating. Also, we can see that the diameter of the hole increases due to this.

From the simple considerations of the structure of a crystalline solid, it can be said that the atoms of the crystal are arranged in a regular array under the elastic force. Between two adjacent atoms, this elastic force behaves like an almost inextensible spring. At a fixed temperature, two atoms thus maintain an average distance between them and vibrate. This average distance increases with the rise in temperature. Hence, solids expand with the rise in temperature.

Note: The thermal expansion of different solids, for the same rise in temperature, is different. For example, copper undergoes a greater thermal expansion than iron, for the same rise in temperature with respect to their initial length, surface, or volume. Again, with the rise in temperature, a solid expands equally in all directions. But there are also few exceptions. A few crystals expand differently in different directions when heated.