Suggested answer

The incidence of a tax refers to who eventually pays a tax. An indirect tax on producers increases their costs and this will lead to an inward shift of the supply curve. Once the tax is imposed, suppliers may then chose to pass on the tax to consumers by raising their selling price. This depends on the coefficient of price elasticity of demand.

When demand is inelastic (i.e. Ped<1), then most of the tax can be passed on. This is because consumers are less sensitive to price changes, e.g. a 20% increase in price might only lead to a 5% contraction in demand. However, when demand is price elastic (i.e. Ped>1), then most of the incidence of a tax is absorbed by the producer. In this situation, only a small proportion of the tax will be paid by the consumer. 

The incidence of an indirect tax also depends on the coefficient of price elasticity of supply.

When supply is perfectly elastic (i.e. Pes= infinity) this means that output can be supplied at constant cost. A tax on producers again causes an inward shift of the supply curve. But in this situation, all of the tax will be paid by the consumer, regardless of the coefficient of PED. When demand is elastic, the consumer pays all of the tax, but equilibrium quantity will contract by a large amount.