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Basics of Electric Circuits, Magnets, and Transformers

Learn about the fundamentals of electric circuits, magnets, and transformers. Understand concepts like voltage, current, resistance, magnetic fields, and energy transfer. Explore the properties of magnets and electromagnets, and how they are used in various applications. Discover how transformers efficiently transfer electrical energy between circuits.

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Basics of Electric Circuits, Magnets, and Transformers

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  1. Last week … • A simple electric circuit consists of • a current source, such as acar battery • a resistor, such as a light bulb, or heater • Voltage drop = Resistance * Current • Power = (Voltage drop) * Current A simple circuit: A battery creates an voltage V which pushes the current i through the resistor R. In the wires, voltage and current are constant. Units: Current in Amperes A Voltage in Volts V Resistance in Ohm Ω

  2. Magnets • Context: Magnetic fields make an electro-motor turn. A compass needle points to the North pole of the earth. • Definition: • A magnetis a material or object that produces a magnetic field. A method to detect a magnetic field is to scatter iron filings and observe their pattern. • Discussion: • Each magnet has a North and a South pole. Opposite poles attract each other, equal poles repel each other. • A "hard" or "permanent" magnet is one that stays magnetized, such as the rock “loadstone” or iron (ferromagnet). • A "soft" or "impermanent" magnet is one that loses its memory of previous magnetizations. • A material without a permanent magnetic moment can, in the presence of magnetic fields, be attracted (paramagnetic: aluminum), or repelled (diamagnetic: graphite, super conductors). Iron filings that have oriented in the magnetic field produced by a bar magnet • Lecture demos: • Load stone • Bar magnet • Broken magnet

  3. Electromagnets • Context: Electric current creates a magnetic field. • Definition: • An electromagnetis a wire coil in which the magnetic field is produced by the flow of an electric current. • Discussion: • When the current is off, there is no magnetic field. When the current changes, the magnetic field changes. • An electromagnet creates a force and a torque on other magnets, including other electromagnets. This can be used to build electro motors. • A changing magnetic field induces a current, and thus a magnetic field in a second coil (magnetic brakes). • The direction of magnetic field in the second coil is opposite to the magnetic field in the first coil (repulsive force  E&M cannon). Iron filings that have oriented in the magnetic field produced by a coil carrying a current • Lecture demos: • - Helmholtz coil • E&M cannon • Faraday effect • Motor 1, Motor 2 • magnetic brake

  4. Transformers • Context: High voltage power lines save energy. • Definition: • A transformer are two coils that transfer electrical energy from one circuit to another through magnetic coupling. A changing current in the first coil (the primary ) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second coil (the secondary). • Discussion: • The secondary induced voltage V2 is scaled from the primary V1 by a factor ideally equal to the ratio of the number of turns of wire in their respective windings (N2, N1): V2/V1 = N2/N1 • Power line: energy loss = resistance * current2 • Energy transferred = voltage * current •  High voltage power lines are energy efficient A transformer (2 coils) reduces The voltage from 10000V to 110V. • Lecture demos: • Transformer • E&M cannon • high voltage power line

  5. Magnets & transformers A magnetis a material or object that produces a magnetic field. A method to detect a magnetic field is to scatter iron filings and observe their pattern. An electromagnet is a wire coil in which the magnetic field is produced by the flow of an electric current. A transformer are two coils that transfer electrical energy from one circuit to another through magnetic coupling. A changing current in the first coil (the primary ) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second coil (the secondary). Iron filings that have oriented in the magnetic field produced by a bar magnet & a coil

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