Rise substantially

In this case, the quantity supplied is the same regardless
of the price. As the elasticity rises, the supply curve gets flatter, which
shows that the quantity supplied responds more to changes in the price. At the opposite
extreme, supply is perfectly elastic. This occurs as the price elasticity of supply
approaches infinity and the supply curve becomes horizontal, meaning that
very small changes in the price lead to very large changes in the quantity supplied.
In some markets, the elasticity of supply is not constant but varies over the
supply curve. Figure 5-7 shows a typical case for an industry in which firms have
factories with a limited capacity for production. For low levels of quantity supplied,
the elasticity of supply is high, indicating that firms respond substantially to
changes in the price. In this region, firms have capacity for production that is not
being used, such as plants and equipment sitting idle for all or part of the day.
Small increases in price make it profitable for firms to begin using this idle capacity.
As the quantity supplied rises, firms begin to reach capacity. Once capacity is
fully used, increasing production further requires the construction of new plants.
To induce firms to incur this extra expense, the price must rise substantially, so
supply becomes less elastic.