7.3
Courbes de coût total fixe, total variable et total
À court terme, une entreprise engage diverses dépenses fixes telles que les paiements de location, les primes d’assurance et l’amortissement des machi…
Prenons l’exemple d’une petite entreprise qui fabrique des tables. À court terme, elle engendre des coûts fixes, notamment la location de l’usine et l’entretien des machines. La somme de ces coûts est appelée coût fixe total (TFC).
Graphiquement, TFC est une ligne horizontale parallèle à l’axe des x, car elle reste constante quelle que soit la sortie.
Les coûts variables comprennent les paiements pour le bois et la main-d’œuvre journalière. La somme de ces coûts est le coût variable total ou TVC.
En l’absence de production, la TVC est nulle. Au fur et à mesure que la fabrication commence, la TVC augmente en raison des coûts du bois et de la main-d’œuvre. En raison de l’augmentation du produit marginal du travail qui existe sur la fourchette initiale de la production initiale, la TVC augmente à un rythme décroissant. Cependant, plus tard, la TVC augmente à un rythme croissant en raison de l’apparition éventuelle d’une diminution du produit marginal du travail. Dans cette gamme de production, les travailleurs peuvent être inactifs, attendant d’avoir accès à des machines limitées, ce qui entraîne une baisse de la productivité.
Le coût total ou TC est la somme de TFC et TVC. TC est similaire à TVC, et ceux-ci sont parallèles. Cependant, TC commence à partir du point de coût fixe total, car il s’agit de coûts encourus indépendamment de la production.
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Q1: What is total fixed cost and why does it remain constant on a cost curve?
Total fixed cost (TFC) represents expenses a firm incurs regardless of output level, such as factory rent and machine maintenance. Graphically, TFC appears as a horizontal line parallel to the x-axis because these costs remain constant whether the firm produces zero units or maximum capacity. This unchanging nature distinguishes fixed costs from variable expenses.
Q2: How does total variable cost behave as production increases?
Total variable cost (TVC) starts at zero when no production occurs and increases as output rises. Initially, TVC increases at a diminishing rate due to increasing marginal product of labor. Later, TVC rises at an accelerating rate when diminishing marginal product of labor sets in, as workers become idle waiting for limited machinery access, reducing overall productivity.
Q3: What expenses are included in total variable cost for a manufacturing firm?
Total variable cost (TVC) includes all expenses that change with production levels, such as raw materials like wood and hourly wage labor payments. These costs directly correlate with output quantity—the more a firm produces, the higher its variable costs become, making them distinct from fixed expenses like rent.
Q4: How is total cost calculated and why is it parallel to the total variable cost curve?
Total cost (TC) equals the sum of total fixed cost (TFC) and total variable cost (TVC). The TC curve is parallel to the TVC curve because the vertical distance between them—the fixed cost—remains constant across all output levels. TC simply shifts the TVC curve upward by the amount of fixed costs incurred.
Q5: Why does the total cost curve start above the origin on a graph?
The total cost curve starts above the origin because it begins at the total fixed cost point. Even when production is zero, the firm still incurs fixed expenses like rent and machine maintenance. This starting point reflects costs the firm must pay regardless of whether any output is produced.
Q6: What causes the shape of the total variable cost curve to change from gentle to steep?
The TVC curve's shape reflects labor productivity changes. Initially, increasing marginal product of labor causes TVC to rise gently at a lower rate. As production expands, diminishing marginal product of labor emerges, causing TVC to rise steeply. Workers experience idle time waiting for limited machinery, reducing efficiency and increasing costs per unit produced.
Q7: How do fixed and variable costs differ in their relationship to production output?
Fixed costs remain constant regardless of output level, while variable costs change directly with production quantity. Fixed costs like rent and machine maintenance are unavoidable short-run expenses, whereas variable costs such as materials and labor scale with production volume. Understanding this distinction is essential for analyzing cost behavior and profitability.