A-Level物理电场与电场力要点详解

A-level所有科目中，A-level物理涉及很多电场、电力等方面的信息，A-Level物理在考试形式上也和国内物理差别很大。A-Level物理只有单选和大题两种体型，大题里包括了计算题和解释题。计算题一般占的分值并不是特别多，以及大部分都是套用公式的运算，难度不大，不会像国内的题目出的那么难，那么灵活。那么接下来新航道小编就给大家整理一下A-Level物理电场与电场力复习要点！

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

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