Negative Externality Diagram Maker
Externality diagrams dominate IB market-failure questions and real-world IA commentaries, carbon taxes, congestion charges, sugar levies. The examiner wants to see marginal social cost diverging from marginal private cost, the welfare loss triangle pointing at the socially optimal output, and any corrective policy drawn in.
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With IB EconGraph AI you can generate a complete negative production externality diagram from one sentence, then adjust the divergence, shade the welfare loss, and add a tax shift, all with exact, consistent intersection points.
What the negative externality diagram shows
A negative production externality diagram (e.g. a polluting factory) shows:
- MPC curve: the private supply curve, costs the producer actually pays.
- MSC curve: above MPC; the vertical gap is the external cost imposed on third parties.
- Market equilibrium (Q₁): where MPC meets demand (MPB), the free-market outcome with overproduction.
- Social optimum (Q*): where MSC meets MSB, the allocatively efficient output.
- Welfare loss: the triangle between MSC and MPB from Q* to Q₁, showing the deadweight loss of overproduction.
How to draw it in IB EconGraph AI
- Prompt the AI with e.g. "negative production externality from a coal plant with welfare loss shaded", or draw MPC first and duplicate it upward for MSC.
- Keep MSC parallel to MPC (a constant marginal external cost) unless your analysis argues the externality grows with output.
- Mark both quantities: the market output Q₁ (D = MPC) and the social optimum Q* (D = MSC), with dotted lines to the axes.
- Shade the welfare loss triangle between the two quantities using the fill tool.
- For policy evaluation, shift MPC up towards MSC to show a Pigouvian tax internalising the externality.
IA & exam tips
- Most IA market-failure commentaries use this exact diagram, customise the labels to your article ("MSC of plastic production") to hit the "application" criterion.
- Distinguish production vs consumption externalities: consumption ones diverge MPB/MSB on the demand side instead.
- When evaluating a tax, note on the diagram whether it fully closes the MPC–MSC gap; partial internalisation is a strong evaluation point.
Frequently asked questions
Can it draw consumption externalities too?
Yes, ask for a negative consumption externality (e.g. cigarettes) and it diverges MPB below MSB instead, with the welfare loss in the right place.
How do I show a corrective (Pigouvian) tax?
Duplicate the MPC curve and shift it up by the tax; the new equilibrium moves toward the social optimum. The tax-incidence template also helps here.
Is this suitable for my IA?
Yes, export vector SVGs that stay sharp at any size in your commentary, with your article-specific labels and figure caption.
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