MagnetismSection 3 Section 3: Electric Currents from Magnetism Preview Key Ideas Bellringer Electromagnetic Induction The Electromagnetic Force Transformers

MagnetismSection 3 Key Ideas 〉 What happens when a magnet is moved into or out of a coil of wire? 〉 How are electricity and magnetism related? 〉 What are the basic components of a transformer?

MagnetismSection 3 Bellringer 1.List as many items as you can that use DC current. (Hint: Batteries supply DC current.) 2.List as many items as you can that use AC current. (Hint: Standard wall outlets supply AC current.) 3.If you want to plug a CD player that normally uses batteries into a wall socket, an AC adapter is required. What is the function of the AC adapter? 4.Electric power that goes into a neighborhood must be stepped down, or decreased, in voltage before it goes into a home. Explain why this is necessary.

MagnetismSection 3 Electromagnetic Induction 〉 What happens when a magnet is moved into or out of a coil of wire? 〉 Moving a magnet into and out of a coil of wire causes charges in the wire to move. electromagnetic induction: the process of creating a current in a circuit by changing a magnetic field Faraday’s law states: An electric current can be produced in a circuit by a changing magnetic field crossing the circuit.

MagnetismSection 3 Electromagnetic Induction, continued As the loop moves in and out of the magnetic field of the magnet, a current is induced in the circuit. Rotating the circuit or changing the strength of the magnetic field will also induce a current in the circuit. Electromagnetic induction obeys conservation of energy. –Pushing a loop through a magnetic field requires work.

MagnetismSection 3 Electromagnetic Induction, continued

MagnetismSection 3 Visual Concept: Ways of Inducing a Current in a Circuit Click the button below to watch the Visual Concept.

MagnetismSection 3 Electromagnetic Induction, continued The magnetic force acts on moving electric charges. –The force is at its maximum value when the charge moves perpendicularly to the field. –As the angle between the charge’s direction and the direction of the magnetic field decreases, the force on the charge decreases. The magnetic force acts on wires carrying a current.

MagnetismSection 3 Electromagnetic Induction, continued

MagnetismSection 3 Electromagnetic Induction, continued Generators convert mechanical energy into electrical energy. generator: a machine that converts mechanical energy to electrical energy alternating current (AC): an electric current that changes direction at regular intervals –For each half rotation of the loop, the current produced by the generator reverses direction. AC generators produce the electrical energy you use in your home.

MagnetismSection 3 AC Generator

MagnetismSection 3 Induced Current

MagnetismSection 3 Visual Concept: Function of a Generator Click the button below to watch the Visual Concept.

MagnetismSection 3 The Electromagnetic Force 〉 How are electricity and magnetism related? 〉 Electricity and magnetism are two aspects of a single force, the electromagnetic force. The energy that results from these two forces is called electromagnetic (EM) energy. Light is a form of electromagnetic energy. EM waves are made up of oscillating electric and magnetic fields that are perpendicular to each other.

MagnetismSection 3 Visual Concept: Electromagnetic Waves Click the button below to watch the Visual Concept.

MagnetismSection 3 Transformers 〉 What are the basic components of a transformer? 〉 In its simplest form, a transformer consists of two coils of wire wrapped around opposite sides of a closed iron loop. transformer: a device that increases or decreases the voltage of alternating current primary coil: wire attached to a source of alternating current secondary circuit: wire attached to an appliance

MagnetismSection 3 Transformers, continued Current in the primary coil, creates a changing magnetic field that magnetizes the iron core. The changing magnetic field of the iron core then induces a current in the secondary coil. Transformers can increase or decrease voltage. –The voltage induced in the secondary coil of a transformer depends on the number of loops, or turns, in the coil.

MagnetismSection 3 Transformers, continued In a step-up transformer, the primary coil has fewer turns than the secondary coil does. –The voltage across the secondary coil is greater than the voltage across the primary coil. In a step-down transformer, the secondary coil has fewer loops than the primary coil does. –The voltage across the secondary coil is lower than the voltage across the primary coil.

MagnetismSection 3 Transformers, continued Transformers must obey the law of conservation of energy. –The current in the secondary coil of a step-up transformer is always less than the current in the primary coil. Transformers are used in the transfer of electrical energy.

MagnetismSection 3 Transformers, continued

MagnetismSection 3 Visual Concept: Transformer Click the button below to watch the Visual Concept.