The ridge lines are the locus of points of an iso-quants where the marginal product of factors is zero. An isoquant is ovalshaped shown in diagram but its area of rational operation lies between the ridge lines. The firm will produce only in those segments of isoquants which are convex to the origin and lie between the ridge lines. They are the locus of points of isoquants where the marginal products (MP) of factors are zero. The upper ridge line implies zero MP of capital and the lower ridge line implies zero MP of labour. The marginal products of factors are negative and the methods of production are inefficient outside the ridge lines. They can be explained through the help of following diagram:
Diagram
In the above Diagram curves ОA and OB are the ridge lines on the oval-shaped iso-quants and in between these line on points G, J, L and N and H, К, M and P economically feasible units of capital and labour can be employed to produce 100, 200, 300 and 400 units of the product.
For example, ОТ units of labour and ST units of the capital can produce 100 units of the product, but the same output can be obtained by using the same quantity of labour ОТ and less quantity of capital VT. Thus, only an unwise producer will produce in the dotted region of the isoquant 100. The dotted segments of isoquants form the uneconomic regions of production because they require an increase in the use of both factors with no corresponding in-crease in output. If points G, J, L, N, H, К, M and P are connected with the lines OA and OB. On both sides of the ridge lines, it is uneconomic for the firm to produce while it is economically feasible to produce inside the ridge lines.
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