Types of Market Structures - Economics

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PERFECT COMPETITION
Short Run Equilibrium of the Firm Under Perfect Competition:  
Definition and Explanation:
 
By short run is meant a length of time which is not enough to change the level of fixed inputs or the number of firms in the industry but long enough to change the level of output by changing variable inputs.  

In short period, a distinction is made of two types of costs (i) fixed cost and (ii) variable cost.  
The fixed cost in the form of fixed factors i.e., plant, machinery, building, etc. does not vary with the change in the output of the firm. If the firm is to increase or decrease its output, the change only takes place in the quantity of variable resources such as labor, raw material, etc.  

Further, in the short run, the demand curve facing the firm is horizontal. No new firms enter or leave the industry. The number of firms in the industry, therefore, remain the same. Under perfect competition, the firm takes the price of the product as determined in the market. The firm sells all its output at the prevailing market price. The firm, in other words, is a price taker.  

Equilibrium of a Competitive Firm:
                       
The short-run equilibrium of a firm can be easily explained with the help of marginal revenue = marginal cost approach or MR= MC rule.  
Marginal revenue is the change in total revenue that occurs in response to a one unit change in the quantity sold. Marginal cost is the addition to total cost resulting from the additional of marginal unit. Since price is given for the competitive firm, the average revenue curve of a price taker firm is identical to the marginal curve. Average revenue (AR) thus is equal to marginal revenue (MR) is equal to price (MR = AR = Price).                     

According to the marginal revenue and marginal cost approach or (MR = MC) rule , a price taker firm is in equilibrium at a point where marginal revenue (MR) or price is equal to marginal cost The point where MR = MC = Price, the firm produces the best level of output. From this it may not be concluded that the perfectly competitive firm at the equilibrium level of output (MR = MC = Price) necessarily ensures maximum profit. The fact is that in the short period, a firm at the equilibrium level of output is faced with four types of product prices in the market which give rise to following results:  

(i) A firm earns supernormal profits.
  
(ii) A firm earns normal profits.
 
(iii) A firm incurs losses but does not close down.
 
(iv) A firm minimizes losses by shutting down. All these short run cases of profits or losses are explained with the help of diagrams.

 
Determining Profit from a Graph:
                  
(1) Profit Maximizing Position:
 
A firm in the short run earns abnormal profits when at the best level of output, the market price exceeds the short run average total cost (SATC). The short run profit maximizing position of a purely competitive firm is explained with the help of a diagram.  

Diagram/Graph:
 

 
In the figure (15.3), output is measured along OX axis and revenue / cost on OY axis. We assume here that the market price is equal to OP. A price taker firm has to sell its entire output at this prevailing market price i.e. OP. The firm is in equilibrium at point L. Where MC = MR. The inter section of MC and MR determine the quantity of the good the firm will produce.  

After having determined the quantity, drop a vertical line down to the horizontal axis and see what the average total cost (ATC) is at that output level (point N). The competitive firm will produce ON quantity of output and sell at market price OP. The total revenue of the firm at the best level of output ON is equal to OPLN. Whereas the total cost of producing ON quantity of output is equal to OKMN. The firm is earning supernormal profits equal to the shaded rectangle KPLM. The per unit profit is indicated by the distance LM or PK.  

It may here be noted that a firm would not produce...
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