摘要：为配合大家更好的复习A-Level考试，老师为大家讲解A-Level物理考试电场与电场力Electric Fields and Forces revision复习要点。希望能够对大家的A-Level考试有所帮助。 Part 1 Electric Field Shapes 电场概念及表示 Electric Field An electric field is a region in which particles with charge experience a force Field Shape Diagrams We represent electric fields with diagrams that have conventions (or r
为配合大家更好的复习A-Level考试，老师为大家讲解A-Level物理考试电场与电场力Electric Fields and Forces revision复习要点。希望能够对大家的A-Level考试有所帮助。
Part 1 Electric Field Shapes 电场概念及表示
Electric Field
“An electric field is a region in which particles with charge experience a force”
Field Shape Diagrams
We represent electric fields with diagrams that have conventions (or rules) that need to be followed.
For example:
The field lines (and arrows) show the direction of the force that would be felt by a positive charge at that point in the field. Note that unlike gravitational fields, electric fields can attract or repel objects.
The spacing between the lines shows how strong the field is at that point. In this case it's strongest near to the charge because the lines are closest there.
This field is uniform because the spacing between the lines remains the same throughout the field shown. The field lines are parallel and equispaced.
Part 2 Electric field strength 电场强度
This is defined as the force per unit charge acting at a point in the field. So an equation for it is:
Where:.
E = electric field strength
F = force acting in newtons
q = the charge in coulombs
Units of E: NC-1 or Vm-1 (these are the same thing!!)
(1)匀强电场Uniform Fields
There is one special example you also need to know :
This is a uniform field. The field strength at any point in this field is:
where
V = the pd between the plates
d = the distance separating the plates.
Field strength is a vector - it has direction as well as magnitude.
This is important to remember because in electric fields you can have field strengths acting in different directions due to different signs of charge.
Radial Fields
A particularly useful equation to find field strength around a point charge (note - the first pictures is the field diagram section were point charges) is:
where
Q = the charge causing the field
r = the separation between the charge and the point you are considering
ε = permittivity (see below for notes).
You can also write this as
This shows that:
A-level课程优势：
· 课程体系：全程服务，20-32小时集训拔高，80小时自主学习与督导指点我们陪你每一分钟
· 课程资料：1）CIE、Edexcel官方教材；2）独家考前押题秘籍；3）2015-2017年考试真题模考精讲；
· 无忧备考：名师授课+作业批改与点评+ 期中、期末模考精讲+24小时答疑+一直到考前也会进行的伴读计划
· 明星师资：授课老师均毕业于美国TOP30名校和国内985名校，IELTS考分8+，同时教授过至少3000个小时的课程
· 教学方法：超过同类机构两倍的刷题量、考前预测各个击破讲练并进，问答结合，真正掌握每一个知识点
针对2018年的A-level考试，开设“A-level基础课程、强化课程、冲刺课程”。想快速提分的同学可以在线咨询客服，了解课程详情，预约名师1V1试听课；为你量身打造专属A-level学习方案；免费领取A-level考试学习资料/视频课件/直播公开课！