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    Grade 12 Physics - Unit 4

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    Grade 12 Physics - Unit 4

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    Grade 12 physics unit 4 note

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    Grade 12 Physics -Unit 4 (2)

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    Grade 12 physics unit 4 note

    Copyright:

    © All Rights Reserved
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    Download as pdf or txt
    7 views4 pages

    Grade 12 Physics - Unit 4

    Uploaded by

    firaolwakjira9
    Grade 12 physics unit 4 note

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 4

    ENTRANCE TRICKS PRIVATE SCHOOL

    Unit 4
    Electromagnetism
    Magnets and Magnetic Fields: Beyond Attraction and Repulsion
    Most of us have encountered magnets in childhood, intrigued by their ability to attract or repel
    certain materials. However, underlying these seemingly simple interactions is a fascinating
    world of magnetic fields that permeate space and exert forces on moving charges.

    Magnetic Fields: Invisible Forces at Play


    Just as electric charges create electric fields, moving charges generate magnetic fields. These
    fields exert forces on other moving charges and magnetic materials. Unlike electric field lines,
    which originate from positive charges and terminate on negative charges, magnetic field lines
    form closed loops. This fundamental difference arises from the fact that isolated magnetic
    poles, known as magnetic mono-poles, have not been observed in nature.

    Visualizing Magnetic Fields


    While invisible to the naked eye, we can visualize magnetic fields using magnetic field lines.
    The sources use diagrams with iron filings sprinkled around magnets to illustrate these lines.
    The iron filings align themselves along the magnetic field lines, revealing the shape and strength
    of the field. The closer together the field lines, the stronger the magnetic field at that point.

    Permanent Magnets vs. Electromagnets


    The sources differentiate between two types of magnets: permanent magnets and
    electromagnets. Permanent magnets, like those we use on refrigerators, retain their
    magnetism over long periods. Electromagnets, on the other hand, generate magnetic fields only
    when an electric current flows through them. This distinction is crucial for understanding the
    operation of devices like electric motors and generators.

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    ENTRANCE TRICKS PRIVATE SCHOOL

    Current and Magnetism: An Intimate Relationship


    For centuries, electricity and magnetism were considered distinct phenomena. However, in the
    early 19th century, scientists discovered a profound link between them: moving electric
    charges create magnetic fields.

    Oersted's Discovery: A Compass Needle's Telltale TwitchThe sources recount Hans Christian
    Oersted's pivotal observation that a compass needle deflects near a current-carrying wire. This
    simple experiment demonstrated that electric currents generate magnetic fields. This
    realization opened the door to harnessing the power of electromagnetism.

    Ampere's Law: Quantifying the Magnetic Force


    Building upon Oersted's discovery, André-Marie Ampere formulated Ampere's Law, which
    quantifies the magnetic field produced by a current-carrying wire. The law states that the
    magnetic field strength around a straight wire is directly proportional to the current and
    inversely proportional to the distance from the wire.

    The Right-Hand Rule: Finding the Magnetic Field Direction


    To determine the direction of the magnetic field around a current-carrying wire, we use the
    right-hand rule. If you point your right thumb in the direction of the conventional current flow
    and curl your fingers, your fingers will point in the direction of the magnetic field lines.

    Electromagnetic Induction: Generating Electricity from Magnetism


    While a changing electric field creates a magnetic field, the reverse is also true: a changing
    magnetic field induces an electric current. This remarkable phenomenon, known as
    electromagnetic induction, forms the foundation for generators, transformers, and countless
    other technologies.

    Faraday's Experiments: A Magnet's Dance with a Coil


    Michael Faraday's experiments demonstrated that moving a magnet near a coil of wire induces
    an electric current in the coil. This discovery revolutionized our understanding of electricity and
    magnetism, demonstrating their interconnected nature.

    Magnetic Flux: Quantifying the Magnetic Field's Influence


    To understand Faraday's Law of induction, we need the concept of magnetic flux (ΦB).
    Magnetic flux through a surface is a measure of the total magnetic field lines passing through
    that surface. It depends on the strength of the magnetic field, the area of the surface, and the
    angle between the magnetic field lines and the surface normal.

    Faraday's Law of Induction: The Induced EMF

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    ENTRANCE TRICKS PRIVATE SCHOOL

    Faraday's Law quantifies electromagnetic induction. It states that the magnitude of the induced
    electromotive force (emf), which drives the induced current, is equal to the rate of change of
    magnetic flux through a circuit:
     ε = -N(ΔΦB/Δt)Where:
     ε is the induced emf.
     N is the number of turns of wire in the coil.
     ΔΦB is the change in magnetic flux.
     Δt is the time interval over which the change occurs.
    The negative sign in Faraday's Law indicates the direction of the induced emf, as explained by
    Lenz's Law.

    Lenz's Law: Nature's Opposition to Change


    Lenz's Law states that the direction of the induced current is such that it opposes the change in
    magnetic flux that produced it. In other words, the induced current creates its own magnetic
    field that tries to counteract the original change in flux.

    Transformers: Manipulating Voltages with Induction


    One of the most important applications of electromagnetic induction is the transformer.
    Transformers allow us to step up (increase) or step down (decrease) AC voltages efficiently.

    How Transformers Work: Two Coils and a Shared Flux


    A transformer consists of two coils of wire, the primary coil and the secondary coil, wrapped
    around a common iron core. When an alternating current flows through the primary coil, it
    creates a changing magnetic flux in the core. This flux then induces an alternating current in the
    secondary coil.

    Voltage Transformation: Turns Ratio is Key


    The ratio of the number of turns of wire in the primary coil (Np) to the number of turns in the
    secondary coil (Ns) determines the voltage transformation ratio:
     Vs/Vp = Ns/Np
    Where:
     Vp and Vs are the primary and secondary voltages, respectively.

    Step-Up and Step-Down: Tailoring Voltage to Our Needs


    Transformers with more turns in the secondary coil than in the primary coil step up the voltage
    (Ns > Np), while those with fewer turns step down the voltage (Ns < Np). Transformers are
    indispensable for power transmission, allowing us to transmit electricity at high voltages (to
    reduce energy losses) and then step down the voltage for safe use in our homes and businesses.

    Applications of Electromagnetism: Technology Shaped by Invisible Forces


    Electromagnetism underpins countless technologies that define the modern world. From the
    electric motors that power our appliances to the generators that produce electricity, our lives
    are intertwined with this fundamental force.

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    ENTRANCE TRICKS PRIVATE SCHOOL

    Electric Motors: Converting Electrical Energy to Mechanical Energy


    Electric motors exploit the interaction between magnetic fields and current-carrying conductors
    to generate rotational motion. The sources provide a simplified explanation of a DC motor's
    operation , highlighting how the magnetic forces between permanent magnets and a current-
    carrying loop create torque, causing the loop to rotate.

    Generators: Electromagnetic Induction in Action


    Generators, essentially electric motors working in reverse, convert mechanical energy into
    electrical energy. Rotating a coil of wire in a magnetic field induces an electric current in the coil,
    generating electricity.

    Beyond Motors and Generators: A World Transformed


    Electromagnetism's impact extends far beyond motors and generators. The sources mention a
    few applications, including:

     Electric bells: Electromagnets are used to move a hammer that strikes a bell, creating sound.
     Magnetic Resonance Imaging (MRI): Strong magnetic fields and radio waves are used to
    create detailed images of the inside of the body.
     Particle accelerators: Electromagnets are used to accelerate charged particles to very high
    speeds for scientific research.
    Safety and Electromagnetism: Respecting the Force
    The sources emphasize the importance of safety when working with electromagnetism. High
    voltages and strong magnetic fields can pose significant risks if not handled properly. Following
    safety guidelines, understanding the equipment being used, and exercising caution are crucial
    to prevent accidents.

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