Chapter 4 Application of Supply and Demand:Elasticity theory A.Elasticity of demand B.Elasticity of supply C.Application of elasticity 1 2023/7117 Economics
1 2023/7/17 Economics Chapter 4 Application of Supply and Demand: Elasticity theory A.Elasticity of demand B.Elasticity of supply C.Application of elasticity
A.Elasticity of Demand Definition and formula Calculation of demand elasticity Categories of demand elasticity ■Elasticity and slope Elasticity and revenue 2 2023/7117 Economics
2 2023/7/17 Economics A.Elasticity of Demand ◼ Definition and formula ◼ Calculation of demand elasticity ◼ Categories of demand elasticity ◼ Elasticity and slope ◼ Elasticity and revenue
Definition and Formula The price elasticity of demand measures how much the quantity demanded of a good changes when its price changes. Usually the price elasticity of demand is the percentage change in quantity demanded divided by the percentage change in price. △Q/Q△QP Ed=一或=一X △PIP △PQ 3 2023/7/17 Economics
3 2023/7/17 Economics Definition and Formula ➢ The price elasticity of demand measures how much the quantity demanded of a good changes when its price changes. ➢ Usually the price elasticity of demand is the percentage change in quantity demanded divided by the percentage change in price. ΔQ/Q ΔQ P Ed = —— 或 = — × — ΔP/P ΔP Q
Calculation of demand elasticity >弧(arc)弹性公式 △Q1(Q+Q2)12 △Q P,+P2 Ed= 或= △P/(P1+P2)2 △P Q1+Q2 >点(point)弹性公式 dQ/Q dQ P Ed=- 或=一X一 dP/P dP Q 4 2023/7117 Economics
4 2023/7/17 Economics Calculation of demand elasticity ➢ 弧(arc)弹性公式 ΔQ/（Q1+Q2）/2 ΔQ P1+P2 Ed = ———————— 或 = — × —— ΔP/（P1+P2）/2 ΔP Q1+Q2 ➢ 点(point)弹性公式 dQ/Q dQ P Ed = —— 或 = —×— dP/P dP Q
弧弹性计算 ■某杂志价格为2元时销售量为5万册，价 格为3元时销售量为3万册，则需求价格 弹性为多少？ 解：价格从2元上涨至3元，Ed=-0.8 价格从3元下降至2元，Ed=2 弧弹性=1.25 5 2023/7/17 Economics
5 2023/7/17 Economics 弧弹性计算 ◼ 某杂志价格为2元时销售量为5万册，价 格为3元时销售量为3万册，则需求价格 弹性为多少？ 解：价格从2元上涨至3元，Ed= -0.8 价格从3元下降至2元，Ed= -2 弧弹性=1.25
点弹性的计算 ■需求函数：Qd=a-bP(a、b为常数，b>0),设 P=1,求点弹性。 解：P=1,则Qd=a-b,另dQdP=-b dQ P 1 b Ed=一X一=-bX一=- dP Q a-ba-b 6 2023/7/17 Economics
6 2023/7/17 Economics 点弹性的计算 ◼ 需求函数：Qd =a-bP (a、b为常数，b>0)，设 P=1，求点弹性。 解：P=1，则Qd = a - b，另dQ/dP= -b dQ P 1 b Ed = —×— = - b × —— = - —— dP Q a – b a – b
Categories of demand elasticity ①Ed=O,Perfectly inelastic demand(需求 完全无弹性) ②0<|Edk1,price-inelastic demand(需求 缺乏弹性) ③lEd=1,unit-elastic demand(需求具有单位 弹性) ④1<Edk∞，price-elastic demand(需求富 有弹性) ⑤lEd=∞，perfectly elastic demand(需求 完全有弹性) 7 2023/7117 Economics
7 2023/7/17 Economics ➢ ①Ed=0，Perfectly inelastic demand(需求 完全无弹性) ➢ ②0<|Ed|<1，price-inelastic demand(需求 缺乏弹性) ➢ ③|Ed|=1，unit-elastic demand(需求具有单位 弹性) ➢ ④1<|Ed|<∞，price-elastic demand(需求富 有弹性) ➢ ⑤|Ed|=∞，perfectly elastic demand(需求 完全有弹性 ) Categories of demand elasticity
需求富有弹性的商品：电话 ■2001年7月1日，国家财政部、产业信息部联合发 文取消了电话初装费，两个多月后，杭州的电话 市场特别是城乡结合部及农村市场出现了空前的 火爆场面。每天前往电信部门登记装电话的客户 络绎不绝，最高一天甚至超过以前一天登记数的 10倍。萧山区甚至出现了一个月发展农村电话27 万户的高峰，一个月新装电话农户就超过以往一 年的数量。淳安县也出现了一天受理装机1485部 的场面。 8 2023/7117 Economics
8 2023/7/17 Economics 需求富有弹性的商品：电话 ◼ 2001年7月1日，国家财政部、产业信息部联合发 文取消了电话初装费，两个多月后，杭州的电话 市场特别是城乡结合部及农村市场出现了空前的 火爆场面。每天前往电信部门登记装电话的客户 络绎不绝，最高一天甚至超过以前一天登记数的 10倍。萧山区甚至出现了一个月发展农村电话2.7 万户的高峰，一个月新装电话农户就超过以往一 年的数量。淳安县也出现了一天受理装机1485部 的场面
Figure 4-1 Categories of demand elasticity P D2 9 2023/7117 Economics
9 2023/7/17 Economics Figure 4-1 Categories of demand elasticity o Q D 1 P D 5 D 2 D 3 D 4 E
Elasticity and slope The same point on different straight-line demand curves has different slopes and elasticities.the elasticities of a point are negatively related to its slopes. >All points on a straight-line demand curve have the same slope,but along this curve,the price elasticity of every point varies from infinity to zero. 10 2023/7117 Economics
10 2023/7/17 Economics Elasticity and slope ➢ The same point on different straight-line demand curves has different slopes and elasticities.the elasticities of a point are negatively related to its slopes. ➢ All points on a straight-line demand curve have the same slope,but along this curve,the price elasticity of every point varies from infinity to zero