MAGNETISM in One Shot | Class 9 Physics | ICSE Board

Magnetism: Introduction

• A magnet is a substance that commonly attracts certain metals. Commonly attracted materials include iron.

• When a magnet is divided, each piece will still exhibit a north and south pole.

• If two magnetic lines intersect, it suggests two different directions.

Overview of the Chapter

• The chapter on magnetism is essential in the 9th-grade syllabus, covering important topics.

• Understanding magnetism is vital as it connects to experiences in everyday life and electricity.

• The class will cover the introduction to magnets, induced magnetism, properties of magnetic fields, and electro-magnets.

• Students are encouraged to utilize their previous knowledge of electricity as it relates to magnetism.

Types of Magnets

Natural vs. Artificial Magnets

• Natural Magnets: Found in nature, like lodestone (iron oxide) found in Magnesia.

• Artificial Magnets: Man-made magnets used for various purposes, typically stronger than natural ones.

• Natural magnets are generally not as strong as artificial magnets, hence their limited applications.

Properties of Magnets

• Every magnet has two poles: North and South.

• If a magnet is cut, the pieces will still have a north and south pole.

• There’s no such thing as a magnetic monopole (a magnet with only one pole).

• Repulsion and Attraction: Similar poles repel each other, while opposite poles attract.

Induced Magnetism

• Induced magnetism occurs when a magnetic material comes in contact with a magnet.

• For example, if a pin is brought near a magnet, it can temporarily become magnetized due to observed magnetic properties.

• This induced magnetism will disappear when the magnet is removed, reverting the material back to being a non-magnetized object.

Magnetic Field Lines

• The magnetic field surrounds a magnet and affects other magnetic materials within that field.

• Characteristics:

  • Direction: Magnetic field lines exit from the north pole and enter at the south pole.

  • Field strength: Areas where lines are close together indicate strong magnetic fields, and areas where they are far apart indicate weak magnetic fields.

  • Magnetic field lines cannot intersect; if they did, it would imply multiple contradictory directions at that point.

Anomalies in Magnetic Fields

• Magnetic fields are vector quantities, indicating both magnitude and direction.

• Earth behaves like a magnet, aligning with traditional magnet models, allowing for navigation (using magnetic compasses).

• Compasses align with Earth’s magnetic field and can change direction when brought near a magnet.

Electromagnetism

• The discovery of electromagnetism began in the early 19th century (around 1820) by Hans Christian Ørsted.

• Current flowing through a wire generates a magnetic field around it, confirmed by compass direction changes.

• Electromagnets: Created by wrapping a wire around a core (usually soft iron) and passing electric current through it.

  • Electromagnets can produce strong magnetic fields and their strength can be enhanced by increasing current, increasing the number of wire turns, or using soft iron cores.

  • The magnetic field lasts only as long as the current flows.

Differences Between Electromagnets and Permanent Magnets

• Electromagnets: Their magnetism is temporary and depends on continuous current flow.

• Permanent Magnets: Maintain their magnetism without the need for electric current.

• Electromagnets allow for flexibility in polarity (north and south can be changed), while permanent magnets have fixed polarity.

• Applications of electromagnets include lifting heavy objects and material transportation, among others.

Conclusion

• Understanding these principles of magnetism is fundamental for practical applications and further studies in physics. Students should remember the relation between electricity and magnetism as they progress in their education.

Magnetism: Introduction

• A magnet is a substance that commonly attracts certain metals, with iron being the most notable example among those materials. Magnets can be natural, such as lodestone, or artificial, which are man-made for various applications.

• When a magnet is divided, each piece retains a north and south pole, showcasing the intrinsic nature of magnetic materials.

• If two magnetic lines intersect, it indicates that the two poles are oriented in different directions, revealing fundamental aspects of magnetism.

Overview of the Chapter

• The chapter on magnetism holds significant importance within the 9th-grade syllabus, covering key topics that build foundational knowledge in physics. Thorough comprehension of magnetism is critical since it connects to real-life experiences and plays a pivotal role in electricity.

• The class will encompass several essential topics, including:

  • The introduction to different types of magnets

  • The concept of induced magnetism

  • The properties and behavior of magnetic fields

  • The functioning and applications of electromagnets

• Students are encouraged to draw on their previous knowledge of electricity to deepen their understanding of how electricity and magnetism are interconnected phenomena.

Types of Magnets

Natural vs. Artificial Magnets

• Natural Magnets: These are found in nature and possess magnetic properties, an example being lodestone, which is composed of iron oxide and was historically significant due to its naturally magnetic characteristics.

• Artificial Magnets: These are man-made magnets that vary in shape, size, and strength, often used in various applications such as motors, generators, and electronic devices. Generally, these are engineered to be stronger than natural magnets, allowing for a wider range of uses due to their enhanced magnetic properties.

Properties of Magnets

• Every magnet possesses two distinct poles: North and South. An important characteristic of magnets is that when a magnet is cut, each resulting piece will still exhibit a north and south pole, emphasizing that poles always exist in pairs.

• It is essential to note that the concept of a magnetic monopole does not exist in nature, meaning no magnet can exist with only one pole.

• Repulsion and Attraction: Similar poles (North-North or South-South) repel each other, while opposite poles (North-South) attract each other. This fundamental behavior is crucial in understanding how magnets interact.

Induced Magnetism

• Induced magnetism occurs when a magnetic material interacts with a magnet. For instance, when a pin is brought near a magnet, it can become temporarily magnetized by the influence of the magnetic field.

• This induced magnetism is not permanent; it vanishes once the magnet is removed, and the material reverts to its non-magnetized state, raising further inquiries into the nature of magnetism and magnetized materials.

Magnetic Field Lines

• The magnetic field surrounds a magnet and influences other magnetic materials within that vicinity. The properties of magnetic field lines include:

  • Direction: Magnetic field lines emanate from the north pole and return at the south pole, illustrating the flow of the magnetic field.

  • Field Strength: Regions where magnetic field lines are densely packed indicate strong magnetic fields, while areas with sparse lines signify weaker fields.

  • Non-intersection: Magnetic field lines cannot intersect; if they did, it would imply the presence of conflicting directions at that specific point.

Anomalies in Magnetic Fields

• Magnetic fields are vector quantities, encompassing both magnitude and direction, and exhibit unique characteristics.

• The Earth itself behaves like a giant magnet, aligning with conventional magnet models, which allows for navigation through the use of magnetic compasses. Compasses align with the Earth’s magnetic field and can change direction when brought near other magnets, underlining the practical implications of magnetic forces.

Electromagnetism

• The field of electromagnetism began its formal discovery in the early 19th century (around 1820) attributed to Hans Christian Ørsted, who observed that electric currents create magnetic fields.

• A current flowing through a conductor generates a magnetic field around it, demonstrated by the observable change of direction in a nearby compass due to the current.

• Electromagnets: These are crafted by coiling a wire around a core, typically soft iron, and allowing an electric current to flow through. Electromagnets can produce potent magnetic fields, with the strength capable of enhancement by increasing the current, increasing the number of turns in the wire, or utilizing better core materials.

• Notably, the generated magnetic field of an electromagnet persists only as long as the current flows, differentiating it from traditional magnets.

Differences Between Electromagnets and Permanent Magnets

• Electromagnets: Their magnetism is temporary — it relies on an ongoing electrical current to maintain magnetic properties.

• Permanent Magnets: These maintain their magnetism independently of electricity, making them ideal for applications where constant magnetism is required.

• Another distinguishing feature of electromagnets is their ability to adjust polarity; the north and south poles can be switched by altering the direction of the current, whereas permanent magnets possess fixed poles.

• Applications of electromagnets are varied and critical in industries, including lifting heavy materials, operating electric motors, and in devices such as magnetic locks.

Conclusion

• Grasping these fundamental principles of magnetism is essential for practical applications in technology, engineering, and physics. Students are encouraged to remember the intricate relationship between electricity and magnetism as they advance in their scientific education, opening the door to further exploration of these interconnected fields.