3. The effect of negative externalities on the optimal quantityof consumption Consider the market for electricity. Suppose that a power plant dumps byproducts into a nearby river, creating a negative externality for those living downstream from the plant. Producing additional electricity imposes a constant per-unit external cost of $240. The following graph shows the demand (private value) curve and the supply (private cost) curve for electricity. Use the purple points (diamond symbol) to plot the social cost curve when the external cost is $240 per unit. (? 800 720 Social Cost 640 560 480 PRICE (Dollars per unit of electricity) 400 Supply Private Cost) 320 O Demand 240 (Private Value) 160 BO 0 5 6 QUANTITY (Units of electricity) The market equilibrium quantity is _ units of electricity, but the socially optimal quantity of electricity production is units. To create an incentive for the firm to produce the socially optimal quantity of electricity, the government could impose a of $ per unit of electricity