Question

Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim
A. Expands and fits onto the wooden wheel.
B. Contracts and fits onto the wooden wheel.
C. No change in the size takes place.
D. Expands first, then on cooling contracts and fits onto the wooden wheel.

Answer 1

Hint: This problem can be solved by learning the properties of metal and its thermal expansion because it is given that the metal given, i.e. iron rim is heated. We can also change these properties of metal by giving a force to metals. We can solve this problem by using this information.

Complete step by step answer:
As we know that iron is a metal. An element, compound or alloy which is a good conductor of heat and electricity is termed as a metal. Metals are generally hard, opaque and have a lustrous character. They have a very high melting point and boiling point. They can be drawn or hammered into wires or sheets. Thermal expansion is the process of changing the shape, area, volume and density by changing the temperature. The rate of thermal expansion depends upon the attractive force between the atoms. When iron metal is heated, it expands and forms into a circular shape. When it is cooled, it comes back into normal shape. Thus the wooden wheels become so tight that it cannot be removed. Iron rims are made smaller than wooden wheels.
When the iron rim is heated, it expands and will have the same size as wooden wheels. When water is poured, the rims become cool and get compressed. Thus it can take the shape of the wooden wheel and gets fixed on the wheels firmly.

Hence the correct option is D.

Note: This problem is purely on the basis of the thermal property of metals to expand on heating and compressing on cooling. This thermal expansion and compression is a reversible change, i.e. both processes can be reversed.