Lesson Notes By Weeks and Term v3 - Senior Secondary 1
Magnet and magnetic field
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Magnet and magnetic field
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Subject: Basic Electronics
Class: Senior Secondary 1
Term: 2nd Term
Week: 4
Theme: Basic Electronic Theory
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Define the following terms:- magnetism- magnetic poles- magnetic field- magnetic materials Differentiate between permanent and temporary magnets Demonstrate the law of at traction and repulsion of a magnet State the applications of magnetism (e.g. Zip drive disk, floppy disk, magnetic tape).
Magnets can be broadly categorized based on how long they retain their magnetic properties after being magnetized.
Permanent Magnets: Definition: These are magnets that retain their magnetic properties for a long period, even after the magnetizing force has been removed.
Characteristics: Made from hard magnetic materials (e.g., steel, cobalt, nickel, alnico alloys). Difficult to magnetize but retain their magnetism strongly once magnetized. Strong magnetic fields. Cannot be easily demagnetized.
Applications: Used in applications where a constant magnetic field is required. Examples include compass needles, loudspeakers, refrigerator door seals, electric meters, and certain types of electric motors.
Temporary Magnets: Definition: These are magnets that retain their magnetic properties only while the magnetizing force is present. They quickly lose their magnetism once the external magnetizing force is removed.
Characteristics: Made from soft magnetic materials (e.g., soft iron). Easy to magnetize and demagnetize. Magnetic field strength can be varied by changing the magnetizing force (e.g., current in an electromagnet). Weak residual magnetism after the magnetizing force is removed.
Applications: Used where magnetic fields need to be turned on and off or varied. Examples include electromagnets in electric bells, relays, circuit breakers, lifting magnets in scrap yards, and telephone receivers. This fundamental law describes how magnetic poles interact with each other.
Statement: "Like poles repel, and unlike poles attract." Explanation: Repulsion: If the North pole of one magnet is brought near the North pole of another magnet, they will push each other away (repel). Similarly, if two South poles are brought near each other, they will repel.
Attraction: If the North pole of one magnet is brought near the South pole of another magnet, they will pull towards each other (attract).
Demonstration (Practical): To demonstrate this, a teacher can use two bar magnets. Suspend one magnet freely by a thread so it can rotate. Bring the North pole of a second magnet close to the North pole of the suspended magnet; the suspended magnet will turn away. Then, bring the South pole of the second magnet close to the North pole of the suspended magnet; the suspended magnet will turn towards it. This clearly illustrates the law. Magnetism plays a vital role in numerous technologies, especially in electronics.
Data Storage: Many traditional and some modern data storage devices rely on magnetism.
Zip Drive Disk / Floppy Disk: These older storage devices used magnetic material coated on a thin disk. Data was stored by magnetizing tiny regions of the disk in specific patterns representing binary 0s and 1s. A read/write head would then detect or alter these magnetic orientations. Magnetic Tape (e.g., cassette tapes, video tapes, backup tapes): Similar to floppy disks, magnetic tapes are thin plastic ribbons coated with a magnetic material. Information (audio, video, or digital data) is recorded by varying the magnetic pattern on the tape as it passes a read/write head.
Hard Disk Drives (HDD): Modern computers still use HDDs, which are highly refined versions of magnetic storage. They use rapidly spinning platters coated with magnetic material, and read/write heads precisely magnetize or detect magnetic changes to store vast amounts of data. Magnetic Strips (e.g., ATM cards, credit cards, ID cards): The dark stripe on the back of these cards is a magnetic strip that stores information (account numbers, cardholder name, expiry date) by magnetizing tiny particles. Card readers can then read this information.
Other Electronic Applications: Loudspeakers and Microphones: Both convert electrical signals into sound (and vice versa) using the interaction between magnetic fields and current-carrying coils.
Electric Motors: Convert electrical energy into mechanical energy by using the force between magnetic fields and current-carrying conductors to produce rotation. (e.g., in fans, blenders, grinding machines common in Nigerian homes/markets).
Generators: Convert mechanical energy into electrical energy using electromagnetic induction.
Transformers: Used to step up or step down AC voltage, relying on magnetic induction between coils wound around a magnetic core.
Relays: Electromagnetically operated switches that use a small current to control a larger current circuit.
Compasses: Used for navigation, relying on the Earth's magnetic field to orient a magnetic needle.
Magnetic Resonance Imaging (MRI): Advanced medical diagnostic tool that uses strong magnetic fields and radio waves to create detailed images of organs and structures inside the body.
Maglev Trains: Use powerful electromagnets to levitate and propel trains at high speeds, although not yet present in Nigeria, they represent a cutting-edge application. This section provides a detailed explanation of the core concepts related to magnets and magnetic fields.
Household Electronics in Nigeria: Many homes in Nigeria use devices that rely on magnetism. Electric Fans, Blenders, Grinding Machines: These appliances utilize electric motors, which operate on the principle of magnetism (interaction between magnetic fields and current-carrying coils) to convert electrical energy into mechanical rotation. This directly impacts daily chores and small businesses.
Radios and Televisions: The loudspeakers in these devices use magnetism to convert electrical signals into sound. Refrigerators use magnetic strips on their doors to create an airtight seal.
Data and Financial Transactions: ATM Cards/Credit Cards: The magnetic stripe on these cards, widely used in Nigeria for banking and transactions, stores sensitive user information. Card readers use magnetism to access and process this data, enabling modern financial operations.
Older Data Storage: While less common now, floppy disks and magnetic tapes were crucial for data storage and backup in earlier Nigerian offices and homes, especially for computer systems and audio/video recordings. Understanding them provides historical context for technology evolution.
Industrial and Commercial Uses: Scrap Metal Recovery: Large electromagnets (temporary magnets) are used in Nigerian scrap yards and waste management facilities to lift and separate magnetic metals (iron, steel) from non-magnetic waste, facilitating recycling and material recovery.
Security Systems: Magnetic sensors are sometimes used in door and window alarms to detect when a circuit is broken by the separation of a magnet from a reed switch.