📚 KS3 CIE Year 8 Electromagnets Scheme of Work | KS3 CIE 八年级电磁铁教学大纲
This unit introduces Year 8 learners to the properties of magnets, the concept of magnetic fields, and the link between electricity and magnetism. Students will build simple electromagnets, investigate the factors that change their strength, and explore how electromagnets are used in everyday devices such as bells, relays, and cranes.
本单元向八年级学生介绍磁铁的性质、磁场的概念以及电与磁之间的联系。学生将制作简单的电磁铁，探究影响其强度的因素，并了解电磁铁在电铃、继电器和起重机等日常设备中的应用。
1. Magnetic Materials and Permanent Magnets | 磁性材料与永磁体
Only a few materials are magnetic: iron, cobalt, nickel, and some alloys such as steel. Most metals like copper, aluminium, and brass are not attracted by magnets.
只有少数材料具有磁性：铁、钴、镍以及钢等一些合金。铜、铝和黄铜等大多数金属不会被磁铁吸引。
A permanent magnet keeps its magnetism for a long time. It has two poles: a north pole and a south pole. Like poles repel, while opposite poles attract.
永磁体可以长时间保持磁性。它有两个磁极：北极和南极。同名磁极相互排斥，异名磁极相互吸引。
The force between two magnets is a non-contact force; it can act through air, paper, or even a thin table.
两块磁铁之间的力是非接触力；它可以通过空气、纸张甚至薄桌面发生作用。
2. Magnetic Fields and Field Lines | 磁场与磁感线
A magnetic field is the region around a magnet where magnetic forces can be detected. Field lines are drawn from the north pole to the south pole outside the magnet.
磁场是磁铁周围能够检测到磁力的区域。磁感线在磁铁外部从北极指向南极。
The closer the field lines, the stronger the magnetic field. The field is strongest near the poles.
磁感线越密集，磁场越强。磁极附近磁场最强。
You can map a field using iron filings or a small plotting compass. The compass needle aligns with the field direction.
你可以使用铁屑或小磁针来描绘磁场。罗盘指针会沿磁场方向排列。
Field lines go from N to S outside a magnet.
磁感线在磁铁外部从 N 极指向 S 极。
3. The Earth's Magnetic Field | 地球的磁场
The Earth behaves like a giant bar magnet. Its magnetic field protects us from charged particles from the Sun.
地球表现得像一个巨大的条形磁铁。它的磁场保护我们免受来自太阳的带电粒子的伤害。
A compass needle points north because the Earth's magnetic south pole is located near the geographic North Pole.
罗盘指针指向北方，是因为地球的磁南极位于地理北极附近。
The angle between true north and magnetic north is called magnetic declination. In navigation, this must be corrected.
真北与磁北之间的夹角称为磁偏角。在导航中必须对其进行修正。
4. Electromagnetism: Current Creates Magnetism | 电磁效应：电流产生磁性
In 1820 Hans Christian Oersted discovered that a wire carrying an electric current produces a magnetic field around it.
1820年，汉斯·克里斯蒂安·奥斯特发现通电导线周围会产生磁场。
The magnetic field around a straight current-carrying wire forms concentric circles. Reversing the current reverses the direction of the field.
通电直导线周围的磁场呈同心圆状。改变电流方向会改变磁场方向。
The right-hand grip rule for a straight wire: point your right thumb in the direction of the current; your fingers curl in the direction of the magnetic field.
直导线右手定则：将右手拇指指向电流方向，手指弯曲的方向即为磁场方向。
Right-hand grip rule: thumb = current, fingers = field direction.
右手定则：拇指指向电流方向，手指弯曲方向为磁场方向。
5. Solenoids and the Right-Hand Grip Rule | 螺线管与右手螺旋定则
A solenoid is a long coil of wire. When current flows through a solenoid, the magnetic fields from each loop add together, creating a strong uniform field inside.
螺线管是一长段绕成线圈的导线。当电流通过螺线管时，每一圈产生的磁场叠加，在内部形成较强的匀强磁场。
The solenoid behaves like a bar magnet. To find the north pole, grip the solenoid with your right hand so that your fingers follow the current direction; your thumb points to the north pole.
螺线管的行为类似于条形磁铁。要找出北极，用右手握住螺线管，让手指沿电流方向弯曲，拇指所指的方向就是北极。
Inserting a soft iron core inside the solenoid makes the magnetic field much stronger because iron is easily magnetised.
在螺线管内部插入软铁芯会使磁场大大增强，因为铁容易被磁化。
Solenoid rule: fingers follow current, thumb points to N pole.
螺线管定则：手指沿电流方向弯曲，拇指指向 N 极。
6. Building an Electromagnet | 制作电磁铁
An electromagnet is made by wrapping insulated wire around a soft iron core. When current flows, the iron core becomes magnetised; when the current stops, the core loses most of its magnetism.
电磁铁由绕在软铁芯上的绝缘导线制成。当电流通过时，铁芯被磁化；当电流停止时，铁芯大部分磁性消失。
Soft iron is used because it is easy to magnetise and demagnetise. Steel would stay magnetised and is used for permanent magnets.
使用软铁是因为它容易被磁化和去磁。钢会保持磁性，因此用于制作永磁体。
A simple classroom electromagnet can be made with a nail, insulated copper wire, and a battery. Always include a switch to avoid overheating.
简单的课堂电磁铁可以用铁钉、绝缘铜线和电池制作。电路中应始终加入开关以避免过热。
7. Factors Affecting Electromagnet Strength | 影响电磁铁强度的因素
The strength of an electromagnet depends on three main factors: the current in the coil, the number of turns of wire, and the material inside the coil.
电磁铁的强度主要取决于三个因素：线圈中的电流、导线的匝数以及线圈内部的材料。
Increasing the current or increasing the number of turns produces more magnetic field lines and a stronger electromagnet.
增大电流或增加匝数会产生更多的磁感线，使电磁铁更强。
A soft iron core greatly increases strength compared with an air core. The core concentrates the magnetic field.
与空芯相比，软铁芯能大大增加强度。铁芯会集中磁场。
Stronger electromagnet = more current + more turns + soft iron core.
更强的电磁铁 = 更大电流 + 更多匝数 + 软铁芯。
8. Applications: Electric Bell and Relay | 应用：电铃与继电器
An electric bell uses an electromagnet to attract an iron armature. When the armature moves, it breaks the circuit, the magnet switches off, and the armature springs back. This repeats rapidly to ring the bell.
电铃利用电磁铁吸引铁质衔铁。当衔铁移动时电路断开，电磁铁断电，衔铁弹回。这一过程快速重复，使铃发声。
A relay is an electrically operated switch. A small current in the electromagnet closes a switch that controls a large current in a separate circuit.
继电器是一种电控开关。电磁铁中的小电流闭合一个开关，从而控制另一个电路中的大电流。
Relays allow a low-voltage circuit to safely control a high-voltage circuit, for example in car starters and industrial machinery.
继电器使低电压电路能够安全地控制高电压电路，例如在汽车起动器和工业机械中。
9. Electromagnetic Cranes and Lifting | 电磁起重机与起重
In a scrapyard, an electromagnetic crane can pick up iron and steel objects. When the current is switched off, the magnet releases the load.
在废料场，电磁起重机可以吸起铁和钢制物体。当切断电流时，磁铁会释放负载。
Electromagnets are useful because they can be switched on and off, and their strength can be adjusted by changing the current.
电磁铁很有用，因为它们可以接通和断开，并且可以通过改变电流来调节强度。
Permanent magnets would be unsuitable for lifting because the load could not be released easily.
永磁体不适合用于起重，因为负载不容易被释放。
10. Comparing Permanent Magnets and Electromagnets | 永磁体与电磁铁的比较
A permanent magnet produces its own magnetic field at all times. It cannot be switched off and its strength is fixed.
永磁体始终产生自身的磁场。它不能关闭，强度也是固定的。
An electromagnet produces a magnetic field only when current flows. Its strength can be changed and its polarity can be reversed by reversing the current.
电磁铁只有在电流通过时才产生磁场。它的强度可以改变，而且通过改变电流方向可以反转极性。
Permanent magnets are made from hard magnetic materials such as steel, while electromagnets use a soft iron core.
永磁体由钢等硬磁材料制成，而电磁铁使用软铁芯。
11. Safety and Circuit Precautions | 安全与电路注意事项
Electromagnet investigations use low-voltage cells, but wires can still become hot if the current is high or the circuit is left on for a long time.
电磁铁实验使用低压电池，但如果电流较大或电路长时间通电，导线仍可能发热。
Always switch off between tests to prevent overheating and to save the battery. Never use mains electricity for electromagnet experiments.
在测试之间务必断开开关，以防止过热并节省电池。切勿在电磁铁实验中使用市电。
Keep the circuit connections firm; a poor connection can produce sparks or cause unreliable results.
保持电路连接牢固；接触不良可能产生电火花或导致实验结果不可靠。
12. Key Practical Skills and Exam Tips | 关键实验技能与应试提示
When planning an investigation to test electromagnet strength, identify the independent variable, dependent variable, and control variables. For example, if you change the number of turns, keep current and core constant.
在规划测试电磁铁强度的探究时，要确定自变量、因变量和控制变量。例如，如果改变线圈匝数，就应保持电流和铁芯不变。
Measure electromagnet strength by counting how many paper clips or pins it can pick up. Repeat each test and calculate a mean.
通过数电磁铁能吸起多少个回形针或大头针来测量其强度。每次测试重复多次并计算平均值。
In exam questions, always link observations to magnetic field direction, polarity, or strength. Use the correct terms: north pole, south pole, field lines, solenoid, soft iron core.
在考试题目中，始终将观察到的现象与磁场方向、极性或强度联系起来。使用正确的术语：北极、南极、磁感线、螺线管、软铁芯。
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