IGCSE物理考点磁讲解 不懂就来看

同学们在日常生活应该会经常见到磁力的情况，同学们有没有想过磁力是如何产生的呢？下面就给大家讲讲IGCSE物理考点之一的磁，有不懂的同学一定要来看看哦，这样才能更好的应对2021年的大考。

 磁的种类：

各种物质可以根据能否被磁化分为两类：Magnetic and non-magnetic materials（磁性和非磁性）

不同性质的磁性物质Types of magnetic material

磁性物质又可以按照其性质不同分为soft和hard，见下图：

如何磁化和消磁

如何把磁性物质磁化（Magnetisation）呢？

我们主要用两种办法:

1. 用磁体的南极或北极，沿物体向一个方向摩擦几次，千万不能改变方向。

A piece of the material may be stroked with a permanent magnet. By stroking it consistently from one end to the other (never going in the reverse direction), it becomes magnetised.

2. 放入强磁场中或者通电。

Place the material in a strong magnetic field, as produced by an electromagnet. An electromagnet is a coil of wire and, for this purpose, it is connected to a battery or power supply so that a steady direct current (d.c.) flows through it. This produces a magnetic field inside the coil, and this field magnetises the material.

反之，要把磁性消除（Demagnetisation），我们可以这么做：

1. 敲他！

Hammer the magnet. When a magnet is placed in an east–west direction and hammered, it loses its magnetism. This explains why the magnets used in school labs gradually lose their magnetism if they are S repeatedly dropped and bashed about.

2. 接入交流电。

Place the magnet in the field of an electromagnet that is connected to an alternating current (a.c.) supply. The magnetic field will vary back and forth. Gradually reduce the current to zero. The magnet will be demagnetised.

3. 把磁铁加热。

Heat the magnet. If its temperature goes above a certain temperature, it will lose its magnetism. 

磁场Magnetic fields

磁场是什么样的呢？我们通常用磁感线来表示磁场。这也是考试中很经常会出现的画图题哦~ 在画图的时候，我们要注意以下四点：

1. 所有的磁感线都是从N到S的闭合曲线 记得要标上箭头表示方向。

2. 两级附近磁场强，所以磁感线也就更紧密。

3. 磁感线不会相交。

4. 磁感线的切线（tangent）表示这点磁场的方向。

通电螺线管Solenoid

通电螺线管的一端是N一端是S，这个由电流方向决定。

有三种可以增强螺线管磁场的方法：

1. 增加电流。

Increase the current flowing through it – the greater

the current, the greater the strength of the field

2. 增加线圈圈数。

Increase the number of turns of wire on the coil – this does not mean making the coil longer, but packing more turns into the same space to concentrate the field

3. 加一个软铁芯。

Add a soft iron core – an iron core becomes strongly magnetised by the field, and this makes the whole magnetic field much stronger.

电磁铁Electromagnets

电磁铁很容易控制，上面有提到各种改变其性质的方法。你想让它有什么、怎么样就可以通过改变一些设置来设计它！

因此，电磁铁经常用作起重装置来吊运钢材，铁砂等导磁材料，或用作电磁机械手夹持钢铁等导磁材。

The electromagnetic cranes that move large pieces of metal and piles of scrap around in a scrapyard. The current is switched on to energise the magnet and pick up the scrap metal. When it has been moved to the correct position, the electromagnet is switched off and the metal is released.

电磁铁还能用在电铃，控制电路，变压器等等上。

Electromagnets are also used in electric doorbells, loudspeakers, electric motors, relays and transformers.

安培定则Right-hand grip rule

安培定则也叫右手螺旋定则，是表示电流和电流激发磁场的磁感线方向间关系的定则。

 通电直导线中的安培定则（安培定则一）：用右手握住通电直导线，让大拇指指向电流的方向，那么四指指向就是磁感线的环绕方向。

通电螺线管中的安培定则（安培定则二）：用右手握住通电螺线管，让四指指向电流的方向，那么大拇指所指的那一端是通电螺线管的N极。

 以上就是磁有关知识点的汇总了，同学们看完是不是觉得没有想象中那么难呢？如果您对IGCSE课程有什么疑问，都可以前来唯寻咨询，唯寻教学团队一定能够给你最好的解答。有需要的同学们点击【预约试听】咨询吧！

了解IGCSE课程点击【IGCSE物理paper4真题来了 将物理的重难点一网打尽】、【CIE和爱德思IGCSE物理课程 哪个A*率更高】。