第8章习题参考答案-第三版-学生版

English Grammar 英语语法第8章 Prepositions 介词第11课 Other Prepositions 其它介词2主讲 TimOBJECTIVES 学习目标重点掌握绿色标记的介词或含介词的短语。

了解英语音乐文化。

12All You Need Is LoveThe Beatles were an English rock band formed in Liverpool in 1960.由......组成The band was composed of four members: John Lennon, Paul McCartney, George Harrison and Ringo Starr.All You Need Is LoveBy early 1964, the Beatles were international stars, leading the "British Invasion" of the United States pop market and breaking numerous sales records.All You Need Is Love随着......的成功Following the success of their eighth album Sgt. Pepper's Lonely Hearts Club Band on May 26th, 1967, the Beatles were at the peak of their popularity at that time.处于......的巅峰All You Need Is LoveThey were invited to perform on a TV program called Our World on behalf of the United Kingdom.The Beatles were asked to provide a song with a message that could be easily understood by everyone, and using "basic English" terms.Unlike a lot of other bands, the Beatles hit the studio on June 14, 1967, 11 days prior to/before the live broadcast. All You Need Is Love was born.代表具有不像提前All You Need Is LoveThe program was broadcast via satellite and watched by people in 25 countries on June 25th, 1967.The show began with the Vienna Boys Choir singing its theme song in 22 different languages , then switched to Canada, the U.S., Japan, and Australia.通过以......开头用22种语言The show returned to London for its final segment: the Beatles performing All You Need is Love.包括They were surrounded by a small orchestra and a group of friends including Mick Jagger as well as Eric Clapton.以及The band played to a pre-recorded backing track instead of/in place of performing the song entirely live,Following the success of its live version, the song was released as a single in July 1967.跟着......弹奏而非作为According to the RIAA (the Recording Industry Association of America), they’re the best-selling band of all-time , with 177 million units sold around the globe.Due to /owing to their contribution to the music industry, they are regarded as the most influential band of all time.根据史上的拥有由于他们对......的贡献被认为是披头士乐队是1960年在利物浦成立的英国摇滚乐队。

第一章糖类1．环状己醛糖有多少个可能的旋光异构体，为什么？[25=32]解：考虑到C1、C2、C3、C4、C5各有两种构象，故总的旋光异构体为25=32个。

2．含D-吡喃半乳糖和D-吡喃葡萄糖的双糖可能有多少个异构体(不包括异头物)?含同样残基的糖蛋白上的二糖链将有多少个异构体?[20；32]解：一个单糖的C1可以与另一单糖的C1、C2、C3、C4、C6形成糖苷键，于是α-D-吡喃半乳基-D-吡喃葡萄糖苷、β-D-吡喃半乳基-D-吡喃葡萄糖苷、α-D-吡喃葡萄糖基-D-吡喃半乳糖苷、β-D-吡喃葡萄糖基-D-吡喃半乳糖苷各有5种，共5×4=20个异构体。

糖蛋白上的二糖链其中一个单糖的C1用于连接多肽，C2、C3、C4、C6用于和另一单糖的C1形成糖苷键，算法同上，共有4×4=16个，考虑到二糖与多肽相连时的异头构象，异构体数目为16×2=32个。

3．写出β-D-脱氧核糖、α-D-半乳糖、β- L-山梨糖和β-D-N-乙酰神经氨酸（唾液酸)的Fischer投影式，Haworth式和构象式。

4．写出下面所示的(A).(B)两个单糖的正规名称(D/L,α/β，f/p),指出(C).(D)两个结构用RS系统表示的构型(R/S)[A、β- D-f-Fru；B、α-L- p-Glc； C、R； D、S]5. L7-葡萄糖的α和β异头物的比旋[αD20]分别为+112.2°和+18.70°。

当α-D-吡喃葡糖晶体样品溶于水时，比旋将由+112.2°降至平衡值+52.70°。

计算平衡混合液中α和β异头物的比率。

假设开链形式和呋喃形式可忽略。

[α异头物的比率为36.5%，β异头物为63.5%]解：设α异头物的比率为x，则有112.2x+18.7(1－x)=52.7,解得x=36.5%，于是(1－x)= 63.5%。

6．将500 mg糖原样品用放射性氰化钾（K14CN)处理，被结合的14CN—正好是0.193μmol，另一500 mg同一糖原样品，用含3% HCl的无水甲醇处理，使之形成还原末端的甲基葡糖苷。

习题88.1 选择题(1) 关于可逆过程和不可逆过程有以下几种说法：①可逆过程一定是准静态过程．②准静态过程一定是可逆过程．③不可逆过程发生后一定找不到另一过程使系统和外界同时复原．④非静态过程一定是不可逆过程．以上说法，正确的是：［］(A) ①、②、③、④. (B) ①、②、③.(C) ②、③、④. (D) ①、③、④.[答案：D. 准静态过程不一定是可逆过程．因准静态过程中可能存在耗散效应，如摩擦、粘滞性、电阻等。

](2) 热力学第一定律表明：［］(A) 系统对外做的功不可能大于系统从外界吸收的热量．(B) 系统内能的增量等于系统从外界吸收的热量．(C) 不可能存在这样的循环过程，在此循环过程中，外界对系统做的功不等于系统传给外界的热量．(D) 热机的效率不可能等于1．[答案：C。

热力学第一定律描述个热力学过程中的能量守恒定性质。

](3) 如题8.1图所示，bca为理想气体绝热过程，b1a和b2a是任意过程，则上述两过程中气体做功与吸收热量的情况是: ［］(A) b1a过程放热，做负功；b2a过程放热，做负功．(B) b1a过程吸热，做负功；b2a过程放热，做负功．(C) b1a过程吸热，做正功；b2a过程吸热，做负功．(D) b1a过程放热，做正功；b2a过程吸热，做正功．题8.1图[答案：B。

b1acb构成正循环，ΔE = 0，A净> 0，Q = Q b1a+ Q acb= A净>0，但Q acb= 0，∴Q b1a >0 吸热; b1a压缩，做负功b2a cb构成逆循环，ΔE = 0，A净< 0，Q = Q b2a+ Q acb= A净<0，但Q acb= 0，∴Q b2a <0 放热; b2a压缩，做负功](4) 根据热力学第二定律判断下列哪种说法是正确的．［］(A) 功可以全部变为热，但热不能全部变为功．(B) 热量能从高温物体传到低温物体，但不能从低温物体传到高温物体．(C) 气体能够自由膨胀，但不能自动收缩．(D) 有规则运动的能量能够变为无规则运动的能量，但无规则运动的能量不能变为有规则运动的能量．[答案：C. 热力学第二定律描述自然热力学过程进行的条件和方向性。

Chapter 8Aggregate Planning in the Supply ChainTrue/False1.The goal of aggregate planning is to satisfy demand in a way thatminimizes profit.Answer: FalseDifficulty: Easy2.Aggregate planning is a process by which a company determines levels ofcapacity, production, subcontracting, inventory, stockouts, and evenpricing over a specified time horizon.Answer: TrueDifficulty: Moderate3.Aggregate planning solves problems involving aggregate decisions ratherthan stock keeping unit (SKU) level decisions.Answer: TrueDifficulty: Easy4.Traditionally, much of aggregate planning is focused within anenterprise and may not always be seen as a part of supply chainmanagement.Answer: TrueDifficulty: Moderate5.Aggregate planning is an important supply chain issue because, to beeffective, it requires inputs from throughout the supply chain, but its results have little impact on the supply chain.Answer: FalseDifficulty: Moderate6.Short-term production serves as a broad blueprint for operations andestablishes the parameters within which aggregate planning decisions are made.Answer: FalseDifficulty: Easy7.The aggregate planning problem is concerned with determining theproduction level, inventory level, and capacity level (internal andoutsourced) for each p eriod that maximizes the firm’s profit over theplanning horizon.Answer: TrueDifficulty: Moderate8.To create an aggregate plan, a company must specify the planning horizonfor the plan and the duration of each period within the planning horizon.Answer: TrueDifficulty: Easy9. A planning horizon is usually between three and five years.Answer: FalseDifficulty: Moderate10. A poor aggregate plan can result in improved sales and profits if theavailable inventory and capacity are unable to meet demand.Answer: FalseDifficulty: Easy11. A poor aggregate plan may result in a large amount of excess inventoryand capacity, thereby raising costs.Answer: TrueDifficulty: Moderate12.The aggregate planner must make a trade-off between capacity, inventory,and backlog costs.Answer: TrueDifficulty: Moderate13.An aggregate plan that increases one cost typically results in theincrease of the other two.Answer: FalseDifficulty: Moderate14.The time flexible strategy is where the production rate is synchronizedwith the demand rate by varying machine capacity or hiring and layingoff employees as the demand rate varies.Answer: FalseDifficulty: Hard15.The time flexible strategy is where workforce (capacity) is kept stablebut the number of hours worked is varied over time in an effort tosynchronize production with demand.Answer: TrueDifficulty: Moderate16.The mixed strategy is where a stable machine capacity and workforce aremaintained with a constant output rate with inventory levels fluctuating over time.Answer: FalseDifficulty: Hard17.Most strategies that an aggregate planner actually uses are incombination, and are referred to as mixed strategies.Answer: TrueDifficulty: Easy18. A highly effective tool for a company to use when it tries to maximizeprofits while being subjected to a series of constraints is aggregateprogramming.Answer: FalseDifficulty: Moderate19.To improve the quality of these aggregate plans, forecast errors must betaken into account when formulating aggregate plans.Answer: TrueDifficulty: Moderate20.Forecasting errors are dealt with in aggregate plans using either safetybacklog or safety capacity.Answer: FalseDifficulty: Moderate21.Safety inventory is defined as inventory held to satisfy demand that ishigher than forecasted.Answer: TrueDifficulty: Easy22.Safety capacity is defined as capacity used to satisfy demand that islower than forecasted.Answer: FalseDifficulty: Easypanies should work with downstream partners to produce forecasts andwith upstream partners to determine constraints when doing aggregateplanning.Answer: TrueDifficulty: Easy24.The aggregate plan should be viewed primarily as an in-house tool thatdoes not need to be communicated to supply chain partners.Answer: FalseDifficulty: Easy25.Given that forecasts are always wrong to some degree, the aggregate planneeds to have some flexibility built into it if it is to be useful.Answer: TrueDifficulty: Moderate26. A manager should perform sensitivity analysis on the inputs into anaggregate plan to choose the best solution for the range ofpossibilities that could occur.Answer: TrueDifficulty: Moderate27.As inputs into the aggregate plan change, managers do not need to makechanges to the aggregate plan.Answer: FalseDifficulty: Easy28.As capacity utilization increases, it becomes less important to performaggregate planning.Answer: FalseDifficulty: ModerateMultiple Choice1.The process by which a company determines levels of capacity, production,subcontracting, inventory, stockouts, and even pricing over a specifiedtime horizon isa.aggregate planning.b.detail planning.c.inventory planning.d.sales planning.e.all of the aboveAnswer: aDifficulty: Moderate2.The goal of aggregate planning is toa.dissatisfy customers in a way that maximizes profit.b.dissatisfy customers in a way that minimizes profit.c.satisfy demand in a way that maximizes profit.d.satisfy demand in a way that minimizes profit.e.none of the aboveAnswer: cDifficulty: Easy3.Aggregate planning solves problems involvinga.aggregate decisions and stock keeping unit (SKU) level decisions.b.aggregate decisions or stock keeping unit (SKU) level decisions.c.aggregate decisions rather than stock keeping unit (SKU) leveldecisions.d.stock keeping unit (SKU) level decisions rather than aggregatedecisions.e. b and c onlyAnswer: cDifficulty: Easy4.Aggregate planning, to be effective, requires inputs froma.all customers.b.all departments.c.all suppliers.d.throughout the supply chain.e.throughout the company.Answer: dDifficulty: Moderate5.Much of aggregate planning has traditionally been focuseda.on short-term production scheduling.b.on customer relationship management.c.within an enterprise.d.beyond enterprise boundaries.e.all of the aboveAnswer: cDifficulty: Moderate6.Which of the following are not operational parameters the aggregateplanner is concerned witha.production rateb.workforcec.overtimed.backorderse.inventory on handAnswer: dDifficulty: Moderate7.The operational parameter concerned with the number of units completedper unit time (such as per week or per month) isa.production rate.b.workforce.c.overtime.d.backlog.e.inventory on hand.Answer: aDifficulty: Easy8.The operational parameter concerned with the number of workers/units ofcapacity needed for production isa.production rate.b.workforce.c.overtime.d.backlog.e.inventory on hand.Answer: bDifficulty: Easy9.The operational parameter concerned with the amount of overtimeproduction planned isa.production rate.b.workforce.c.overtime.d.backlog.e.inventory on hand.Answer: cDifficulty: Easy10.The operational parameter concerned with demand not satisfied in theperiod in which it arises, but carried over to future periods isa.production rate.b.workforce.c.overtime.d.backlog.e.inventory on hand.Answer: dDifficulty: Easy11.The operational parameter concerned with the planned inventory carriedover the various periods in the planning horizon isa.production rate.b.workforce.c.overtime.d.backlog.e.inventory on hand.Answer: eDifficulty: Easy12.The operational parameter concerned with the number of units of machinecapacity needed for production isa.machine capacity level.b.subcontracting.c.overtime.d.backlog.e.inventory on hand.Answer: aDifficulty: Easy13.The operational parameter concerned with the subcontracted capacityrequired over the planning horizon isa.machine capacity level.b.subcontracting.c.overtime.d.backlog.e.inventory on hand.Answer: cDifficulty: Easy14.The aggregate plana.serves as a broad blueprint for operations.b.establishes the parameters within which short-term production anddistribution decisions are made.c.allows the supply chain to alter capacity allocations and changesupply contracts.d.all of the abovee. b and c onlyAnswer: dDifficulty: Moderate15.Aggregate planning is concerned with determininga.the production level, sales level, and capacity for each period.b.the demand level, inventory level, and capacity for each period.c.the production level, inventory level, and capacity for eachperiod.d.the production level, staffing level, and capacity for eachperiod.e.none of the aboveAnswer: cDifficulty: Moderate16.To create an aggregate plan, a company must specifya.the planning horizon for the plan.b.the duration of each period within the planning horizon.c.key information required.d.all of the abovee. a and b onlyAnswer: dDifficulty: Moderate17.The planning horizon isa.the time period over which the aggregate plan is to produce asolution.b.the duration of each time period in the aggregate plan.c.the length of time required to produce the aggregate plan.d.the solution to the aggregate plan.e.none of the aboveAnswer: aDifficulty: Easy18.The length of the planning horizon is usually betweena.one and three months.b.three and eighteen months.c.one and three years.d.three and five years.e.none of the aboveAnswer: bDifficulty: Moderate19.Which of the following is not information needed by the aggregateplannera.demand forecast for each period in the planning horizonb.production costsbor costsd.cost of subcontracting productione.cost of changing the demand forecastAnswer: eDifficulty: Moderate20.The cost of changing capacity includes thea.cost of adding machine capacity.b.cost of reducing machine capacity.c.cost of hiring workforce.d.cost of laying off workforce.e.all of the aboveAnswer: eDifficulty: Easy21.Which of the following is not a cost of changing capacitya.cost of adding machine capacityb.cost of hiring workforcec.cost of laying off workforced.cost of overtimee.cost of reducing machine capacityAnswer: dDifficulty: Moderate22.Which of the following is not a constraint the aggregate planner needsto considera.limits on stockouts and backlogsb.limits on overtimec.limits on sales commissionsd.limits on layoffse.limits on capital availableAnswer: cDifficulty: Moderate23. A poor aggregate plan can result ina.appropriate inventory levels.b.efficient use of capacity.c.better sales and lost profits.d.lost sales and lost profits.e.lost sales and better profits.Answer: dDifficulty: Hard24.The fundamental trade-offs available to an aggregate planner are betweena.capability, inventory, and backlog costs.b.capability, inventory, and sales costs.c.capacity, inventory, and backlog costs.d.capacity, inventory, and sales costs.e.none of the aboveAnswer: cDifficulty: Easy25.Which of the following is not a distinct aggregate planning strategy forachieving balance between capacity, inventory, and backlog costsa.adjustable strategyb.Chase strategyc.level strategyd.mixed strategye.time flexible strategyAnswer: aDifficulty: Easy26.The strategy where the production rate is synchronized with the demandrate by varying machine capacity or hiring and laying off employees asthe demand rate varies is thea.adjustable strategy.b.Chase strategy.c.level strategy.d.mixed strategy.e.time flexible strategy.Answer: bDifficulty: Moderate27.The strategy where workforce (capacity) is kept stable but the number ofhours worked is varied over time in an effort to synchronize production with demand is thea.adjustable strategy.b.Chase strategy.c.level strategy.d.mixed strategy.e.time flexible strategy.Answer: eDifficulty: Moderate28.The strategy where a stable machine capacity and workforce aremaintained with a constant output rate, with inventory levelsfluctuating over time, is thea.adjustable strategy.b.Chase strategy.c.level strategy.d.mixed strategy.e.time flexible strategy.Answer: cDifficulty: Hard29.Most strategies that an aggregate planner actually uses are incombination and are referred to as thea.adjustable strategy.b.Chase strategy.c.level strategy.d.mixed strategy.e.time flexible strategy.Answer: dDifficulty: Easy30. A highly effective tool for a company to use when it tries to maximizeprofits while being subjected to a series of constraints isa.aggregate programming.b.distribution programming.c.production programming.d.linear programming.e.manufacturing programming.Answer: dDifficulty: Moderate31.When formulating aggregate plans,a.forecast errors have no impact.b.forecast errors must be taken into account.c.forecast accuracy is assumed.d.forecast accuracy is not a factor.e.none of the aboveAnswer: bDifficulty: Moderate32.Forecasting errors are dealt with usinga.safety backlog.b.safety capacity.c.safety inventory.d.all of the abovee. b and c onlyAnswer: eDifficulty: Moderate33.Inventory held to satisfy demand that is higher than forecasted isa.safety backlog.b.safety capacity.c.safety inventory.d.safety sales.e.safety workforce.Answer: cDifficulty: Easy34.Capacity used to satisfy demand that is higher than forecasted isa.safety backlog.b.safety capacity.c.safety inventory.d.safety sales.e.safety workforce.Answer: bDifficulty: Easy35.Which of the following is an approach a company can use to create abuffer for forecast error using safety inventorya.overtimeb.carry extra workforce permanentlyc.build and carry extra inventoriesd.subcontractinge.purchase capacity or product from an open or spot marketAnswer: aDifficulty: Easy36.Which of the following is not an approach a company can use to create abuffer for forecast error using safety capacitya.overtimeb.carry extra workforce permanentlyc.build and carry extra inventoriesd.subcontractinge.purchase capacity or product from an open or spot marketAnswer: cDifficulty: Easy37.Aggregate planning should consider information froma.only the enterprise as its breadth of scope.b.downstream partners to produce forecasts.c.upstream partners to determine constraints.d.all of the abovee. b and c onlyAnswer: dDifficulty: Easy38.The quality of the aggregate plan can be improved by using informationfroma.only the local firm.b.only downstream partners.c.only upstream partners.d.all parts of the supply chain.e.none of the aboveAnswer: bDifficulty: Moderate39.The aggregate plan should be communicated toa.only the local firm.b.only downstream partners.c.only upstream partners.d.all supply chain partners who will be affected by it.e.none of the aboveAnswer: cDifficulty: Moderate40.The aggregate plan needs toa.be a final product because changes are disruptive to the supplychain.b.be considered fixed because forecasts are usually accurate.c.have some flexibility built into it because forecasts are alwayswrong.d.have some flexibility built into it because forecasts are usuallyright.e.none of the aboveAnswer: cDifficulty: Moderate41.How frequently should the aggregate plan be reruna.weeklyb.monthlyc.every 3 to 8 monthsd.as inputs to the aggregate plan changee.neverAnswer: dDifficulty: Hard42.As capacity utilization increases,a.it becomes less important to perform aggregate planning.b.it becomes more important to perform aggregate planning.c.it does not affect the importance of performing aggregateplanning.d.it lessens the importance of aggregate planning.e.none of the aboveAnswer: bDifficulty: ModerateEssay/Problems1.Discuss the primary objective and operational parameters of aggregateplanning.Answer: The goal of aggregate planning is to satisfy demand in a waythat maximizes profit. Aggregate planning is a process by which acompany determines levels of capacity, production, subcontracting,inventory, stockouts, and even pricing over a specified time horizon.The aggregate planner’s main objective is to identify the followingoperational parameters over the specified time horizon:•Production rate: the number of units completed per unit time (such as per week or per month).•Workforce: the number of workers/units of capacity needed forproduction.•Overtime: the amount of overtime production planned.•Machine capacity level: the number of units of machine capacityneeded for production.•Subcontracting: the subcontracted capacity required over the planning horizon.•Backlog: demand not satisfied in the period in which it arises butcarried over to future periods.•Inventory on hand: the planned inventory carried over the variousperiods in the planning horizon.The aggregate plan serves as a broad blueprint for operations andestablishes the parameters within which short-term production anddistribution decisions are made. The aggregate plan allows the supplychain to alter capacity allocations and change supply contracts.Difficulty: Moderate2.Discuss the information required for aggregate planning.Answer: An aggregate planner requires the following information:• Demand forecast F t for each Period t in the planning horizon thatextends over T periods• Production costs• Labor costs, regular time ($/hour), and overtime costs ($/hour)• Cost of subcontracting production ($/unit or $/hour)• Cost of changing capacity; specifically, cost of hiring/laying offworkforce ($/worker) and cost of adding or reducing machine capacity($/machine)• Labor/machine hours required per unit• Inventory holding cost ($/unit/period)• Stockout or backlog cost ($/unit/period)• Constraints:• Limits on overtime• Limits on layoffs• Limits on capital available• Limits on stockouts and backlogs• Constraints from suppliers to the enterpriseThis information is used to create an aggregate plan that in turn helpsa company make the following determinations:•Production quantity from regular time, overtime, andsubcontracted time: used to determine number of workers andsupplier purchase levels.•Inventory held: used to determine how much warehouse space andworking capital is needed.•Backlog/stockout quantity: used to determine what the customerservice levels will be.•Workforce hired/laid off: used to determine any labor issuesthat will be encountered.•Machine capacity increase/decrease: used to determine if newproduction equipment needs to be purchased or idled.The quality of an aggregate plan has a significant impact on theprofitability of a firm. A poor aggregate plan can result in lost sales and lost profits if the available inventory and capacity are unable tomeet demand. A poor aggregate plan may also result in a large amount of excess inventory and capacity, thereby raising costs. Therefore,aggregate planning is a very important tool in helping a supply chainmaximize profitability.Difficulty: Hard3.Explain the basic strategies that an aggregate planner has available tobalance the various costs and meet demand.Answer: There are essentially three distinct aggregate planningstrategies for achieving balance between these costs. These strategies involve trade-offs between capital investment, workforce size, work hours, inventory, and backlogs/lost sales. Most strategies that aplanner actually uses are a combination of these three and are referred to as mixed strategies. The three strategies are as follows:1. Chase strategy—using capacity as the lever: With this strategy, the production rate is synchronized with the demand rate by varying machine capacity or hiring and laying off employees as the demand rate varies.In practice, achieving this synchronization can be very problematic because of the difficulty in varying capacity and workforce on short notice. This strategy can be expensive to implement if the cost of varying machine or labor capacity over time is high. It can also have a significant negative impact on the morale of the workforce. The Chase strategy results in low levels of inventory in the supply chain and high levels of change in capacity and workforce. It should be used when the cost of carrying inventory is very expensive and costs to change levels of machine and labor capacity are low.2. Time flexibility strategy—using utilization as the lever: This strategy may be used if there is excess machine capacity ., if machines are not used twenty four hours a day, seven days a week). In this case, the workforce (capacity) is kept stable but the number of hours workedis varied over time in an effort to synchronize production with demand.A planner can use variable amounts of overtime or a flexible schedule to achieve this synchronization. Although this strategy does require that the workforce be flexible, it avoids some of the problems associatedwith the Chase strategy, most notably changing the size of the workforce.This strategy results in low levels of inventory but with lower average utilization. It should be used when inventory carrying costs arerelatively high and machine capacity is relatively inexpensive.3. Level strategy—using inventory as the lever: With this strategy, astable machine capacity and workforce are maintained with a constantoutput rate. Shortages and surpluses result in inventory levelsfluctuating over time. Here production is not synchronized with demand.Either inventories are built up in anticipation of future demand orbacklogs are carried over from high- to low-demand periods. Employeesbenefit from stable working conditions. A drawback associated with this strategy is that large inventories may accumulate and customer ordersmay be delayed. This strategy keeps capacity and costs of changingcapacity relatively low. It should be used when inventory carrying andbacklog costs are relatively low.Difficulty: Moderate4.Discuss key issues to be considered when implementing aggregate planning.Answer: 1. Think beyond the enterprise to the entire supply chain. Most aggregate planning done today takes only the enterprise as its breadthof scope. However, there are many factors outside the enterprisethroughout the supply chain that can dramatically impact the optimalaggregate plan. Therefore, avoid the trap of only thinking about yourenterprise when aggregate planning. Work with partners downstream toproduce forecasts, with upstream partners to determine constraints, and with any other supply chain entities that can improve the quality of the inputs into the aggregate plan. As the plan is only as good as thequality of the inputs, using the supply chain to increase the quality ofthe inputs will greatly improve the quality of the aggregate plan. Also make sure to communicate the aggregate plan to all supply chain partners who will be affected by it.2. Make plans flexible because forecasts are always wrong. Aggregate plans are based on forecasts of future demand. Given that theseforecasts are always wrong to some degree, the aggregate plan needs to have some flexibility built into it if it is to be useful. By building flexibility into the plan, when future demand changes, or other changes occur, such as increases in costs, the plan can appropriately adjust to handle the new situation. A manager should perform sensitivity analysis on the inputs into an aggregate plan. Using sensitivity analysis on the inputs into the aggregate plan will enable the planner to choose thebest solution for the range of possibilities that could occur.3. Rerun the aggregate plan as new data emerges. Aggregate plans providea map for the next three to eighteen months. This does not mean that a firm should only run aggregate plans once every three to eighteen months. As inputs into the aggregate plan change, managers should use the latest values of these inputs and rerun the aggregate plan. By using the latest inputs, the plan will avoid suboptimization based on old data and will produce a better solution. For instance, as new demand forecasts become available, aggregate plans should be reevaluated.4. Use aggregate planning as capacity utilization increases. Surprisingly, many companies do not create aggregate plans and instead rely solely on orders from their distributors or warehouses to determine their production schedules. These orders are driven either by actual demand or through inventory management algorithms. If a company has no trouble efficiently meeting demand this way, then one could claim thelack of aggregate planning may not significantly harm the company. However, when utilization becomes high and capacity is an issue, relying on orders to set the production schedule can lead to capacity problems. When utilization is high, the likelihood of producing for all the orders as they arrive is very low. Planning needs to be done to best utilize the capacity to meet the forecasted demand. Therefore, as capacity utilization increases, it becomes more important to perform aggregate planning.Difficulty: Moderate。

第3册全新版大学英语综合教程Unit8课后答案第3册全新版大学英语综合教程Unit8课后答案全新版大学英语综合教程在内容设计上每单元围绕一个反映当代生活实际的主题展开，同时兼顾语言知识、应用技能、学习策略和跨文化交际等方面内容的有机融合，指导学生全面深入地获取并掌握与各主题有关的`语言文化知识及丰富的语料。

下面是店铺分享的全新版大学英语综合教程3答案，欢迎大家阅读!Text AContent questions1.at his mother’s funeral, the writer swore that one day he’d do something about conditions like hers2.one night,the writer went out for dreinks with another gentleman whose father had died of ALS. They talked about their parents then and wanted to do something as a legacy for them. The stem cell research company Stemagen thus came into existence3.they are concerned about the reproductive possibilities of cloning when Dolly was born4.human reproductive cloning is ethically wrong because the majority of reproductive clones in other species are actually abnormal,with very high miscarriage rates, very high stillbirth rates, fetal anomalies, death soon after birth,etc.5.the writer shows a positive attitude towards therapeutic cloning. He holds that therapeutic cloning does not involve any type of rist to human life and actually provides tremendous potential for the relief of suffering in human beings who are undergoing some awful things.6.the writer honestly thinks that someone will attempt human reproductive cloning and there is no way to stop it7.because by doing so, they could make cloning very real so that people around the world know that cloning is coming along8.their purpose in creating disease-specific stem cell lines is to study the causes of specific diseases,and then research a variety of treatments for these diseases. If the stem cell lines are created for any given individual and are later transplated back into the individual, they will not be rejected by the individual.9.the writer holds that in reality it is transcendent because when you look through the microscope, you see what you may have looked like a long ago, at least in part10.it brought teras to his eyes because the research was done for his mother,and he realized that if she had only been able to live a few years longer, maybe they could have used this technology to help her11.in the process of analysis, the embroys were destroyed by necessity. In other words, to get the genetic material from inside the cells to analyze it, they had to destroy the cell\12.because the writer thinks that logically, an embryo is not life, although it is a potential life. The vast majorityof embroys never become life—they just generate , don't implant and dieLanguage sense enhancement1) in some ways 2)make the most of 3)individual 4)replicated 5)roadmap 6)in place 7) resulst from 8)dissuade 9)Quite honestly 10)legislateVocabulary1.1) complications 2)tremendous 3)brillian 4)analysis \5)transplant , transplant 6)In a sense 7)consented 8)In some ways 9)eyesight10)in reality 11)implanted 12) procedures2. 1)focus 2)come forward 3)result from 4)go through5)carry out 6)work on 7)feed on 8)settled over3. 1)resulted from a childhood illness2)was condemmed by the trade unions as endangering jobs3)in place,even those with presistent, long-term mental illness can usually learn to manage their symptoms and live productive lives4)but apparently showed disapproval of his behaviour5)you should make the most of any advice which you can get from the interviewer4. 1)misconceptions, potential, make the most of ,2)donated, cntentious issue, and opponents3)a fraud , in some ways, condemn himII Collocation1)permission to adopt her2)a willingness to restart peace talks3)failure to find meaning in life4)his determination to realize his ideals5)attempt to blow up the bridge6)an opportunity to pursue a college degree下载文档润稿写作咨询。

Unit Eight: Computer NetworksUnit Eight/Section AI. Fill in the blanks with the information given in the text:1. MAN2. open; closed3. bus4. token5. Ethernet6. client/server7. equals; temporary8. networkII. Translate the following terms or phrases from English into Chinese and vice versa:1. file server 文件服务器2. carrier sense 载波检测，载波监听3. protocol suite 协议组，协议集4. peer-to-peer model 对等模型5. bus topology network 总线拓扑网络6. inter-machine cooperation 机器间合作，计算机间合作7. Ethernet protocol collection 以太网协议集8. proprietary network 专有网络9. utility package 实用软件包，公用程序包10. star network 星形网络11. 局域网local area network (LAN)12. 令牌环token ring13. 无线网络wireless network14. 封闭式网络closed network15. 环形拓扑结构ring topology16. 客户机/服务器模型client/server model17. 网络应用程序network application18. 进程间通信interprocess communication19. 打印服务器print server20. 广域网wide area network (WAN)III. Fill in each of the blanks with one of the words given in the following list, making changes if necessary:Computers can communicate with other computers through a series of connections and associated hardware called a network. The advantage of a network is that data can be exchanged rapidly, and software and hardware resources, such as hard-disk space or printers, can be shared. Networks also allow remote use of a computer by a user who cannot physically access the computer.One type of network, a local area network (LAN), consists of several PCs or workstations connected to a special computer called a server, often within the same building or office complex. The server stores and manages programs and data. A server often contains all of a networked group’s data and enables LAN workstations or PCs to be set up without largestorage capabilities. In this scenario (方案), each PC may have “local”memory (for example, a hard drive) specific to itself, but the bulk of storage resides on the server. This reduces the cost of the workstation or PC because less expensive computers can be purchased, and it simplifies the maintenance of software because the software resides only on the server rather than on each individual workstation or PC.IV. Translate the following passage from English into Chinese:在计算机科学中，网络是指由通信设备连接在一起的一组计算机及其相关设备。

第八章 多元函数的定义1．求下列函数的定义域，并作图表示：（1）arcsin 3xz =+ （2）()2ln 48;z y x =-+（3）z x = （4）z =（5）)0;z R r =>>（6）z =解答： 本题图略（1）30,03,0,0;x x y y -≤≤≤≤⎧⎧⎨⎨≤≥⎩⎩ （2）()242y x >-；（3）,0x y <+∞≤<+∞；（4）x ≥且0y ≥；（5）2222r x y R <+≤； （6） 1.xy >所属章节：第八章第一节 难度：一级2．试用不等式表示由抛物线2y x =和2y x =所围成的区域（含边界）。

解答：201,x x y ≤≤≤≤ 所属章节：第八章第一节 难度：一级3．设(),,x f x y xy y=+求1,32f ⎛⎫⎪⎝⎭及()1,1.f - 解答：()15,3,1,1 2.23f f ⎛⎫=-=- ⎪⎝⎭所属章节：第八章第一节 难度：一级4．设()22,tan ,xf x y x y xy y=+-求(),.f tx ty解答：()()2,,.f tx ty t f x y = 所属章节：第八章第一节 难度：一级5．设22,,x f x y x y y ⎛⎫+=- ⎪⎝⎭求(),.f x y解答： 令11uv u x y x v xv u y y v ⎧=+⎧=⎪⎪⎪+⇒⎨⎨=⎪⎪=⎩⎪+⎩，代入原式得 222(1)(,)()()111uv u u v f u v v v v -=-=+++，即2(1)(,)1x y f x y y -=+注：如果题目是“设22,,y f x y x x y ⎛⎫=⎪⎭-+ ⎝求(),.f x y ”则答案为令11u u x y x v yuv v y x v ⎧=+=⎧⎪⎪⎪+⇒⎨⎨=⎪⎪=⎩⎪+⎩ ，代入原式得 222(1)(,)()()111u uv u v f u v v v v -=-=+++，即2(1)(,)1x y f x y y -=+。

大学物理学第三版下册习题标准答案习题8习题八8-1电量都是q的三个点电荷，分别放在正三角形的三个顶点．试问：(1)在这三角形的中心放一个什么样的电荷，就可以使这四个电荷都达到平衡(即每个电荷受其他三个电荷的库仑力之和都为零)(2)这种平衡与三角形的边长有无关系解:如题8-1图示(1)以A处点电荷为研究对象，由力平衡知：q"为负电荷20220)33(3-="(2)与三角形边长无关．题8-1图题8-2图8-2两小球的质量都是m，都用长为l的细绳挂在同一点，它们带有相同电量，静止时两线夹角为2θ,如题8-2图所示．设小球的半径和线的质量都可以忽略不计，求每个小球所带的电量．解:如题8-2图示⎪⎪⎪⎪⎪===220)in2(π41incoθεθθlqFTmgTe解得θπεθtan4in20mglq=8-3根据点电荷场强公式204rqEπε=，当被考察的场点距源点电荷很近(r→0)时，则场强→∞，这是没有物理意义的，对此应如何理解解:020π4rrqEε=仅对点电荷成立，当0→r时，带电体不能再视为点电荷，再用上式求场强是错误的，实际带电体有一定形状大小，考虑电荷在带电体上的分布求出的场强不会是无限大．8-4在真空中有A，B两平行板，相对距离为d，板面积为S，其带电量分别为+q和-q．则这两板之间有相互作用力f，有人说f=2024dqπε,又有人说，因为f=qE,SqE0ε=，所以f=Sq02ε．试问这两种说法对吗为什么f到底应等于多少解:题中的两种说法均不对．第一种说法中把两带电板视为点电荷是不对的，第二种说法把合场强SqE0ε=看成是一个带电板在另一带电板处的场强也是不对的．正确解答应为一个板的电场为SqE02ε=，另一板受它的作用力SqSqqf02022εε==，这是两板间相互作用的电场力．8-5一电偶极子的电矩为lqp=，场点到偶极子中心O点的距离为r,矢量r与l的夹角为θ,(见题8-5图)，且lr>>．试证P点的场强E在r方向上的分量rE和垂直于r的分量θE分别为rE=302corpπεθ,θE=304inrpπεθ证:如题8-5所示，将p分解为与r平行的分量θinp 和垂直于r的分量θinp．∵lr>>∴场点P在r方向场强分量30π2corpErεθ=垂直于r方向，即θ方向场强分量300π4inrpEεθ=题8-5图题8-6图8-6长l=15.0cm的直导线AB上均匀地分布着线密度λ=5.0某10-9C·m-1的正电荷．试求：(1)在导线的延长线上与导线B端相距1a=5.0cm处P 点的场强；(2)在导线的垂直平分线上与导线中点相距2d=5.0cm处Q点的场强．解：如题8-6图所示(1)在带电直线上取线元某d，其上电量qd在P 点产生场强为20)(dπ41d某a某EP-=λε2220)(dπ4d某a某EEllPP-==⎪⎪-ελ]2121[π40lala+--=ελ)4(π220lal-=ελ用15=lcm，9100.5-⨯=λ1mC-⋅,5.12=acm代入得21074.6⨯=PE1CN-⋅方向水平向右(2)同理2220ddπ41d+=某某EQλε方向如题8-6图所示由于对称性⎪=lQ某E0d，即QE只有y分量，∵22222220ddddπ41d++=某某某EQyλε22π4ddελ⎪==lQyQyEE⎪-+2223222)d(dll某某2220d4π2+=llελ以9100.5-⨯=λ1cmC-⋅,15=lcm,5d2=cm代入得21096.14⨯==QyQEE1CN-⋅，方向沿y轴正向8-7一个半径为R的均匀带电半圆环，电荷线密度为λ,求环心处O 点的场强．解:如8-7图在圆上取ϕRddl=题8-7图ϕλλdddRlq==，它在O点产生场强大小为20π4ddRREεϕλ=方向沿半径向外则ϕϕελϕdinπ4indd0REE某==ϕϕελϕπdcoπ4)co(dd0REEy-=-=积分RRE某000π2dinπ4ελϕϕελπ==⎪0dcoπ400=-=⎪ϕϕελπREy∴REE某0π2ελ==，方向沿某轴正向．8-8均匀带电的细线弯成正方形，边长为l，总电量为q．(1)求这正方形轴线上离中心为r处的场强E；(2)证明：在lr>>处，它相当于点电荷q产生的场强E．解:如8-8图示，正方形一条边上电荷4q在P点产生物强PEd方向如图，大小为()4π4cocod22022lrEP+-=εθθλ∵22co221l+=θ12cocoθθ-=∴24π4d2222lrllrEP+=ελPEd在垂直于平面上的分量βcoddPEE=⊥∴424π4222222lrrlrlrlE+++=ελ题8-8图由于对称性，P点场强沿OP方向，大小为2)4(π44d42222lrllrEEP++=⨯=⊥ελ∵lq 4=λ2) 4(π42222lrlrqrEP++=方向沿OP8-9(1)点电荷q位于一边长为a的立方体中心，试求在该点电荷电场中穿过立方体的一个面的电通量；(2)如果该场源点电荷移动到该立方体的一个顶点上，这时穿过立方体各面的电通量是多少某(3)如题8-9(3)图所示，在点电荷q的电场中取半径为R的圆平面．q在该平面轴线上的A 点处，求：通过圆平面的电通量．(某Rarctan=α)解:(1)由高斯定理dεqSE⎪⋅立方体六个面，当q在立方体中心时，每个面上电通量相等∴各面电通量06εqe=Φ．(2)电荷在顶点时，将立方体延伸为边长a2的立方体，使q处于边长a2的立方体中心，则边长a2的正方形上电通量06εqe=Φ对于边长a的正方形，如果它不包含q所在的顶点，则024εqe=Φ，如果它包含q所在顶点则0=Φe．如题8-9(a)图所示．题8-9(3)图题8-9(a)图题8-9(b)图题8-9(c)图(3)∵通过半径为R的圆平面的电通量等于通过半径为22某R+的球冠面的电通量，球冠面积某]1)[(π22222某R某某RS+-+=∴)(π42200某RSq+=Φε02εq=[221某R某+-]某关于球冠面积的计算：见题8-9(c)图ααα⎪⋅=0dinπ2rrSααα⎪⋅=02dinπ2r)co1(π22α-=r8-10均匀带电球壳内半径6cm，外半径10cm，电荷体密度为2某510-C·m-3求距球心5cm，8cm,12cm各点的场强．解:高斯定理0dε∑⎪=⋅qSE,02π4ε∑=qrE当5=rcm时，0=∑q,0=E8=rcm时，∑q3π4p=3(r)3内r-∴()2023π43π4rrrEερ内-=41048.3⨯≈1CN-⋅，方向沿半径向外．12=rcm时,3π4∑=ρq-3(外r）内3r∴()420331010.4π43π4⨯≈-=rrrEερ内外1CN-⋅沿半径向外.8-11半径为1R和2R(2R＞1R)的两无限长同轴圆柱面，单位长度上分别带有电量λ和-λ,试求:(1)r＜1R；(2)1R＜r ＜2R；(3)r＞2R处各点的场强．解:高斯定理0dε∑⎪=⋅qSE取同轴圆柱形高斯面，侧面积rlSπ2=则rlESESπ2d=⋅⎪对(1)1Rr<0,0==∑Eq(2)21RrR<<λlq=∑∴rE0π2ελ=沿径向向外(3)2Rr>0=∑q∴0=E题8-12图8-12两个无限大的平行平面都均匀带电，电荷的面密度分别为1σ和2σ，试求空间各处场强．解:如题8-12图示，两带电平面均匀带电，电荷面密度分别为1σ与2σ，两面间，nE)(21210σσε-=1σ面外，nE)(21210σσε+-=2σ面外，nE)(21210σσε+=n：垂直于两平面由1σ面指为2σ面．8-13半径为R的均匀带电球体内的电荷体密度为ρ,若在球内挖去一块半径为r＜R的小球体，如题8-13图所示．试求：两球心O与O"点的场强，并证明小球空腔内的电场是均匀的．解:将此带电体看作带正电ρ的均匀球与带电ρ-的均匀小球的组合，见题8-13图(a)．(1)ρ+球在O点产生电场010=E，ρ-球在O点产生电场"dπ4π3430320OOrEερ=∴O点电场"d33030OOrEερ=；(2)ρ+在O"产生电场"dπ4d3430301OOEερπ="ρ-球在O"产生电场002="E∴O"点电场003ερ="E"OO题8-13图(a)题8-13图(b)(3)设空腔任一点P相对O"的位矢为r"，相对O点位矢为r(如题8-13(b)图)则03ερrEPO=，03ερrEOP"-=",∴0003"3)(3ερερερdOOrrEEEOPPOP=="-=+="∴腔内场强是均匀的．8-14一电偶极子由q=1.0某10-6C的两个异号点电荷组成，两电荷距离d=0.2cm，把这电偶极子放在1.0某105N·C-1的外电场中，求外电场作用于电偶极子上的最大力矩．解:∵电偶极子p在外场E中受力矩EpM⨯=∴qlEpEM==ma某代入数字4536ma某100.2100.1102100.1---⨯=⨯⨯⨯⨯⨯=MmN⋅8-15两点电荷1q=1.5某10-8C，2q=3.0某10-8C，相距1r=42cm，要把它们之间的距离变为2r=25cm，需作多少功解:⎪⎪==⋅=222102120外力需作的功61055.6-⨯-=-="AAJ题8-16图8-16如题8-16图所示，在A，B两点处放有电量分别为+q,-q的点电荷，AB间距离为2R，现将另一正试验点电荷0q从O点经过半圆弧移到C 点，求移动过程中电场力作的功．解:如题8-16图示0π41ε=OU0)(=-RqRq0π41ε=OU)3(RqRq-Rq0π6ε-=则θλddRq=产生O点Ed如图，由于对称性，O点场强沿y轴负方向题8-17图θεθλππcoπ4dd2220⎪⎪-==RREEyR0π4ελ=［)2in(π-2inπ-］R0π2ελ-=(2)AB电荷在O点产生电势，以0=∞U⎪⎪===AB200012lnπ4π4dπ4dRR某某某某Uελελελ同理CD产生2lnπ40 2ελ=U半圆环产生0034π4πελελ==RRU∴0032142lnπ2ελελ+=++=UUUUO8-18一电子绕一带均匀电荷的长直导线以2某104m·-1的匀速率作圆周运动．求带电直线上的线电荷密度．(电子质量0m=9.1某10-31 kg，电子电量e=1.60某10-19C)解:设均匀带电直线电荷密度为λ，在电子轨道处场强rE0π2ελ=电子受力大小reeEFe0π2ελ==∴rvmre20π2=ελ得1320105.12π2-⨯==emvελ1mC-⋅8-19空气可以承受的场强的最大值为E=30kV·cm-1，超过这个数值时空气要发生火花放电．今有一高压平行板电容器，极板间距离为d=0.5cm，求此电容器可承受的最高电压．解:平行板电容器内部近似为均匀电场∴4105.1d⨯==EUV8-20根据场强E与电势U的关系UE-∇=，求下列电场的场强：(1)点电荷q的电场；(2)总电量为q，半径为R的均匀带电圆环轴上一点；某(3)偶极子qlp=的lr>>处(见题8-20图)．解:(1)点电荷rqU0π4ε=题8-20图∴0200π4rrqrrUEε=∂∂-=0r为r方向单位矢量．(2)总电量q，半径为R的均匀带电圆环轴上一点电势220π4某RqU+=ε∴()i某Rq某i某UE2/3220π4+=∂∂-=ε(3)偶极子lqp=在lr>>处的一点电势200π4co])co21(1)co2(1[π4rqlllrqUεθθθε=+--=∴30π2corprUErεθ=∂∂-=30π4in1rpUrEεθθθ=∂∂-=8-21证明：对于两个无限大的平行平面带电导体板(题8-21图)来说，(1)相向的两面上，电荷的面密度总是大小相等而符号相反；(2)相背的两面上，电荷的面密度总是大小相等而符号相同．证:如题8-21图所示，设两导体A、B的四个平面均匀带电的电荷面密度依次为1σ，2σ，3σ，4σ题8-21图(1)则取与平面垂直且底面分别在A、B内部的闭合柱面为高斯面时，有0)(d32=∆+=⋅⎪SSEσσ∴+2σ03=σ说明相向两面上电荷面密度大小相等、符号相反；(2)在A内部任取一点P，则其场强为零，并且它是由四个均匀带电平面产生的场强叠加而成的，即0222204030201=---εσεσεσεσ又∵+2σ03=σ∴1σ4σ=说明相背两面上电荷面密度总是大小相等，符号相同．8-22三个平行金属板A，B和C的面积都是200cm2，A和B相距4.0mm，A与C相距2.0mm．B，C都接地，如题8-22图所示．如果使A板带正电3.0某10-7C，略去边缘效应，问B板和C板上的感应电荷各是多少以地的电势为零，则A板的电势是多少解:如题8-22图示，令A板左侧面电荷面密度为1σ，右侧面电荷面密度为2σ题8-22图(1)∵ABACUU=，即∴ABABACACEEdd=∴2dd21===ACABABACEEσσ且1σ+2σSqA=得,32SqA=σSqA321=σ而7110232-⨯-=-=-=ACqSqσCC10172-⨯-=-=SqBσ(2)301103.2dd⨯===ACACACAEUεσV8-23两个半径分别为1R和2R（1R＜2R)的同心薄金属球壳，现给内球壳带电+q，试计算：(1)外球壳上的电荷分布及电势大小；(2)先把外球壳接地，然后断开接地线重新绝缘，此时外球壳的电荷分布及电势；某(3)再使内球壳接地，此时内球壳上的电荷以及外球壳上的电势的改变量．解:(1)内球带电q+；球壳内表面带电则为q-,外表面带电为q+，且均匀分布，其电势题8-23图⎪⎪∞∞==⋅=22020π4π4ddRRRqrrqrEUεε(2)外壳接地时，外表面电荷q+入地，外表面不带电，内表面电荷仍为q-．所以球壳电势由内球q+与内表面q-产生：0π4π42022=-=RqRqUεε(3)设此时内球壳带电量为q"；则外壳内表面带电量为q"-，外壳外表面带π4"π4"π4"21=-=8-24半径为R的金属球离地面很远，并用导线与地相联，在与球心相距为Rd3=处有一点电荷+q，试求：金属球上的感应电荷的电量．解:如题8-24图所示，设金属球感应电荷为q"，则球接地时电势0=OU8-24图由电势叠加原理有：=OU03π4π4"00=+RqRqεε得-="q3q8-25有三个大小相同的金属小球，小球1，2带有等量同号电荷，相距甚远，其间的库仑力为0F．试求：(1)用带绝缘柄的不带电小球3先后分别接触1，2后移去，小球1，2之间的库仑力；(2)小球3依次交替接触小球1，2很多次后移去，小球1，2之间的库仑力．解:由题意知2020π4rqFε=2与小球3均带电3=""∴此时小球1与小球2间相互作用力00220222q.∴小球1、2间的作用力0029题8-26图⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪⎪++++==+=+-==+=+===+6543215432065430021001σσσσσσσσσσεσσσσεσσdUSqSqdUUCSSqBA解得Sq261==σσSqdU2032-=-=εσσSqdU2054+=-=εσσ所以CB间电场SqdUE00422εεσ+==)2d(212d02SqUEUUCBCε+===注意：因为C片带电，所以2UUC≠，若C片不带电，显然2UUC=8-27在半径为1R的金属球之外包有一层外半径为2R的均匀电介质球壳，介质相对介电常数为rε，金属球带电Q．试求：(1)电介质内、外的场强；(2)电介质层内、外的电势；(3)金属球的电势．解:利用有介质时的高斯定理∑⎪=⋅qSDSd(1)介质内)(21RrR<303π4,π4rrQErrQDrεε==内;介质外)(2Rr303π4,π4rrQErQrDε==外(2)介质外)(2Rr>电势rQEU0rπ4rdε=⋅=⎪∞外介质内)(21RrR<2020π4)11(π4RQRrqrεεε+-=1(π420RrQrr-+=εεε(3)金属球的电势rdrd221⋅+⋅=⎪⎪∞RRREEU外内⎪⎪∞+=22220π44πdrRRRrrQdrrQεεε)11(π4210RRQrr-+=εεε8-28如题8-28图所示，在平行板电容器的一半容积内充入相对介电常数为rε的电介质．试求：在有电介质部分和无电介质部分极板上自由电荷面密度的比值．rdrd⋅+⋅=⎪⎪∞∞rrEEU外内解:如题8-28图所示，充满电介质部分场强为2E，真空部分场强为1E，自由电荷面密度分别为2σ与1σ由∑⎪=⋅0dqSD得11σ=D，22σ=D而101EDε=,202EDrεε=d21UEE==∴rDDεσσ==1212题8-28图题8-29图8-29两个同轴的圆柱面，长度均为l，半径分别为1R和2R(2R＞1R)，且l>>2R-1R，两柱面之间充有介电常数ε的均匀电介质.当两圆柱面分别带等量异号电荷Q和-Q时，求：(1)在半径r处(1R＜r＜2R＝，厚度为dr，长为l的圆柱薄壳中任一点的电场能量密度和整个薄壳中的电场能量；(2)电介质中的总电场能量；(3)圆柱形电容器的电容．解:取半径为r的同轴圆柱面)(S则rlDSDSπ2d)(=⋅⎪当)(21RrR<∴rlQDπ2=(1)电场能量密度22222π82lrQDwεε==薄壳中rlrQrlrlrQwWεευπ4ddπ2π8dd22222===(2)电介质中总电场能量⎪⎪===211222lnπ4π4ddRRVRRlQrlrQWWεε(3)电容：∵CQW22=∴)/ln(π22122RRlWQCε==某8-30金属球壳A和B的中心相距为r，A和B原来都不带电．现在A的中心放一点电荷1q，在B的中心放一点电荷2q，如题8-30图所示．试求：(1)1q对2q作用的库仑力，2q有无加速度；(2)去掉金属壳B，求1q作用在2q上的库仑力，此时2q有无加速度．解:(1)1q作用在2q的库仑力仍满足库仑定律，即2为零，没有加速度．(2)去掉金属壳B，题8-30图题8-31图8-31如题8-31图所示，1C=0.25μF，2C=0.15μF，3C=0.20μF．1C上电压为50V．求：ABU．解:电容1C上电量111UCQ=电容2C与3C并联3223CCC+=∴355025某某某某某某某某某⨯===CUCCQU86)35251(5021=+=+=UUUABV8-321C和2C两电容器分别标明“200pF、500V”和“300pF、900V”，把它们串联起来后等值电容是多少如果两端加上1000V的电压，是否会击穿解:(1)1C与2C串联后电容1203002003002002121=+⨯=+="CCCCCpF(2)串联后电压比231221==CCUU，而100021=+UU∴6001=UV,4002=UV即电容1C电压超过耐压值会击穿，然后2C也击穿．8-33将两个电容器1C和2C充电到相等的电压U以后切断电源，再将每一电容器的正极板与另一电容器的负极板相联．试求：(1)每个电容器的最终电荷；(2)电场能量的损失．解:如题8-33图所示，设联接后两电容器带电分别为1q,2q题8-33图则⎪⎪⎪⎪⎪⎪⎪==-=-=+212解得(1)=1qUCCCCCqUCCCCC21212221211)(,)(+-=+-(2)电场能量损失WWW-=∆0)22()2121(2221212221CqCqUCUC+-+=221212UCCCC+=8-34半径为1R=2.0cm的导体球，外套有一同心的导体球壳，壳的内、外半径分别为2R=4.0cm和3R=5.0cm，当内球带电荷Q=3.0某10-8C时，求：(1)整个电场储存的能量；(2)如果将导体壳接地，计算储存的能量；(3)此电容器的电容值．解:如图，内球带电Q，外球壳内表面带电Q-，外表面带电Q题8-34图(1)在1Rr0=E在21RrR<3Rr>时302π4rrQEε=∴在21RrR<1dπ4)π4(21222001RRrrrQWεε⎪-==21)11(π8π8d2102202RRRRQrrQεε在3Rr>区域⎪∞==32302220021π8dπ4)π4(21RRQrrrQWεεε∴总能量)111(π83 210221RRRQWWW+-=+=ε41082.1-⨯=J(2)导体壳接地时，只有21RrR<rQEε=,02=W∴4210211001.1)11(π8-⨯=-==RRQWWεJ(3)电容器电容)11/(π422 102RRQWC-==ε121049.4-⨯=F。