Describe the atomic theory of elasticity. 

The atoms or molecules are bounded by interatomic and intermolecular forces and are in stable equilibrium whenever a perfect state is acquired. In a perfect equilibrium state, the separation is such that the net interatomic intermolecular force is zero. When a body is heated, cooled or any physical factors leads to any change in its state, the distance between the two atoms or molecules increases and attractive force comes into play. When the separation between the atoms or molecules decreases the repulsive force comes into play.
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Plot the graph between intermolecular forces. What is the range of these forces?

The range of intermolecular forces is the distance upto which the influence of one molecule can be experienced by other. Range is different for different substances. It is of the order


The range of intermolecular forces is the distance upto which the inf
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What is yield point and why it is so named? 

Yield point is also known as elastic limit. Beyond the elastic limit, when the load is increased, a stress is reached where the material continues to deform without any further increase in load. This point is called yield point. Since at yield point the deformation continues to increase without increase in stress, thus it may be said that there is total surrender of material to stress. The synonym of surrender is yield, that is why this point is called yield point. 
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What is stress and what is its origin?

When an external force is applied on the body there is a deformation in it's shape. The deformation in the shape is due to relative change in the position of atoms or molecules. This relative change in the position causes the attractive or repulsive interatomic or intermolecular forces to set up in the solid which is called restoring force. This restoring force is the origin of stress. The restoring force per unit area is called stress.

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Amorphous substances do not have sharp melting point but get softening range before melting, while crystalline substances have sharp melting point. Explain.


Amorphous substances possess short-range arrangement of atoms or molecules. These short and ordered arrangement disappears gradually on heating. Before melting, this gradual change makes the amorphous substance soft.

While in crystalline substances, there is a long-range order arrangement of atoms or molecules. This arrangement disappears at a definite temperature and hence have sharp melting points. 
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