详细了解一下ALevel经济学考点中
Alevel 物理中我们所学过的波粒二象性是很多同学的梦魇，本来波就很难理解了，再加上粒子的特性，很多同学对这部分的理解一直紧紧停留在表面上，那么今天，我们在这里对波粒二象性进行一个剖析，帮助同学们一探究竟； 所谓波粒二象性其实是量子物理中最著名的思想之一，这里的波粒二象性其实指的是物质既是波又是粒子，这个理论其实从粒子的角度来解释，可以理解为用像的位置，动量的大小和方向来描述他们；从波的角度意味着在场中的传播。 在我们的Alevel课本（CIE）我们对于波粒二象性的解释实现从波的特性开始的，然后是从粒子特性解释了物质； 但是在历史的发展中却不是这样的：在最早约公元前500年古希腊的哲学家，提出光是有一股非常非常小的微粒构成，在接下来的几百年中，对于粒子特性的支持中最有名的莫过于艾萨克·牛顿 （没错，又是他） 虽然他承认单个光电子在碰撞时候会像波一样存在彼此干扰，但是本质上讲光还是粒子，受其影响，粒子说一直保持很长时间的影响，但是苦于当时的实验设备比较落后，所以理论学说的存在也就是看谁的影响力大，并没有足够的实验来支撑这个理论，直到测量设备的改进，这个理论被彻底压制了。 这个实验就是大名鼎鼎的托马斯·杨于1802年进行的双峰干涉实验（Alevel同学应该很熟悉了） ▲双缝干涉实验及其图案 实验可以简单描述为光照射在拥有两条非常窄缝隙的光屏上，两条窄缝的间距很小，透过这两个窄缝的光照在光屏后方的屏幕上呈现出了明暗相间的条纹。 我们可以假设如果光是由直线运动的粒子组成，那么在窄缝后的屏幕上看到的应该是两条亮线，但是现实却不是这样的，我们实际看到的如上图右侧的图样，杨认为这样的明暗相间的条纹是由于两束相干波的干涉效果造成的 并运用强大的数学计算，证明了这种相互干涉是由于波的特性造成的。 ▲双缝干涉实验示意图 至此，光的波动学说开始广泛传播，整个过程持续了四五百年的历史，这个理论也得到了学术界的公认，也经受住了所有的挑战，下次，咱们看看究竟又是什么实验，让光的粒子性再次进入人们的视野，被大众认可的。
A-level考试培训
New
A-level OPENS
A-level预习
A-level
课程亮点
1
爱德思和AQA注册认证的考培中心
2
顾问1V1全方位指导，制定专属学习计划
3
使用原版教材和九天独家辅导资料
4
实体教学环境，沉浸式高效学习
学科
经济类
经济学、会计、商务
自然科学类
物理、化学、生物、科学
人文社科类
地理、历史、心理学、社会学
数学及计算机类
数学、高等数学、计算机科学
语言类
英文文学、英文语言、雅思
课程适合人群
1
适用阶段
（1）欲就读于英国或英联邦体系国际学校A-level阶段的学生
（2）有英语基础但对A-level认识不够全面的学生
A-level OPENS
2
学习收获
（1）课前顾问对学生学习能力1对1评估，量身打造课程，帮助学生充分完成课前预习
（2）课中导师双语沟通，对原版教材进行知识点精讲，帮助学生提前适应国外上课方式
（3）课后完成多样化作业并进行学术测试，班主任线上线下24小时答疑
A-level OPENS
详细了解一下ALevel经济学考点中
商品分类是指根据一定的管理目的，为满足商品生产、流通、消费活动的全部或部分需要，将管理范围内的商品集合总体，以所选择的适当的商品基本特征作为分类标志，逐次归纳为若干个范围更小、特质更趋一致的子集合体（类目），例如大类、中类、小类、细类，直至品种、细目等，从而使该范围内所有商品得以明确区分与体系化的过程。今天未来小编就带大家一起来详细了解一下ALevel经济学考点中，有关商品类别的介绍。 ALevel经济学考点 Economic goods/free goods Economic good(private good)-A good which imposes some cost on society to produce.It is a good that is limited and will have anopportunity cost. Free good-A good which can be enjoyed without any cost to society.It is a good that is unlimited and has no opportunity cost.For example,air to breathe,rain water(in most parts of the world)。 Example of free good vs economic good If you get a meal that costs?0,that doesn’t make it a free good.In this case,you got the mealfor free,but it was still a cost to someone else in society.To grow the food,we used up limited farming land.It is an economic good.However,if you go swimming in the sea,this can be considered a free good,as there is no cost. Public goods Public goods are missing from the free market,but they offer benefits to society.For example,street lights and flood control systems are public goods. They are non-excludable so by consuming the good,some one else is not prevented from consuming the good as well,and they are non-rival,so the benefit other people get from the good does not diminish if more people consume the good. The non-excludable nature of public goods gives rise to the free-rider problem.Therefore,people who do not pay for the good still receive benefits from it,in the same way people who pay for the good do.This is why public goods are under provided by the private sector:they do not make a profit from providing the good since consumers do not see areas on to pay for the good,if they still receive the benefit without paying. Public goods are also under provided because it is difficult to measure the value consumers get from public goods,so it is hard to put a price on the good.Consumers will under value the benefit,so they can pay less,whilst producers will over value,so they can charge more. Governments provide public goods,and they have to estimate what the social benefit of the public good is when deciding what output of the good to provide.They are funded using tax revenue,but the quantity provided will be less than the socially optimum quantity. Private goods Private property rights can be used to prevent others from consuming the good.Private goods are rival and excludable.For example,a chocolate bar can only be consumed by one consumer. Quasi(non-pure)public goods They have characteristics of both public and private goods.They are partially provided by the free market.For example,roads are semi-excludable,through tolls and they are semi-non-rival,because consumers can benefit from the road whilst other consumers are using it(unless it is rush hour)。 Merit good A merit good occurs where people may under estimate or be unaware of the benefits of consuming a good. Positive externalities are caused by merit goods.These are associated with information failure too,because consumers donot realize the long run benefits to consuming the good.They are unde rprovided in a free market.For example,education and healthcareare merit goods.The positive externality to third parties of education is a higher skilled workforce. Demerit good A demerit good occurs where people under estimate or ignore the costs of consuming a good. Negative externalities are caused by demerit goods.These are associated with information failure,since consumersare not aware of the long run implications of consuming the good,and they are usually over provided.For example,cigarettes and alcohol are demerit goods.The negative externality to third parties of consuming cigarettes issecond-hand smoke or passive smoking. 教育作为国际课程辅导中心（A-level、IGCSE、IB、AP等国际课程），是中国专业、值得信赖的国际课程学习中心，是中国学生通往海外顶尖名校的桥梁。（海淀校区），（国贸校区）
