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Three resistors are connected in a circuit, with resistances of 15.0 Ω, 5.0 Ω, and 3.0 Ω. Calculate all of the possible equivalent resistances. Consider series, parallel, and combined circuits.
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Fuse Box or Circuit Breaker? GFCI’s?
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Chapter 24
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Magnets have two poles, named North and South If free to rotate, magnets will align with Earth’s magnetic north and south poles A magnet can be temporary or permanent Opposite poles attract, like poles repel Magnets are attracted to most (but not all) metals Permanent magnets can temporarily pass some magnetism to another metal
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A ferromagnet is a magnet made of a ferromagnetic metal, such as iron, cobalt, or nickel. Created inside a magnetic field.
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Splitting a magnet creates smaller magnets that each have a north pole and south pole.
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Earth’s magnetic field: ~4x10 -5 T Refrigerator magnet: ~5x10 -3 T Neodymium magnet: ~1.2 T Large Hadron Collider: 8.4 T Magnetic resonance imager: ~10 T B>100 T is very rare on Earth
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Earth’s magnetic field: ~4x10 -5 T
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How do we know that Earth’s magnetic field has changed direction?
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You have the rest of class to work on: Check your answers to Chapter 22-23 bookwork Chapter 22 Review Chapter 23 Review
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Moving charges produce magnetic fields. Magnetic fields affect moving charges.
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If a current is flowing through a wire perpendicular to a magnetic field, it will experience a force given by: F = Force (Newtons) I = current (Amperes) L = length of the wire (meters) B = magnetic field strength (Teslas)
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A wire that is 75 cm long, carrying a current of 6.0 A, is at right angles to a uniform magnetic field. The magnitude of the force acting on the wire is 0.60 N. What is the strength of the magnetic field? 0.13 T
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A 40.0 cm long copper wire carries a current of 5.5 A and weighs 0.30 N. A certain magnetic field is strong enough to balance the force of gravity on the wire. What is the strength of the magnetic field? 0.14 T
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An electron passes through a magnetic field at a velocity of 4.0x10 6 m/s. The strength of the magnetic field is 0.50 T. What is the magnitude of the force acting on the electron? 3.2x10 -13 N
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A stream of ions missing one electron moves at a velocity of 3.0x10 4 m/s perpendicular to a magnetic field of 9.0x10 2 T. What is the magnitude of the force acting on each ion? 4.3x10 -12 N
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Currents produce magnetic fields The direction of the magnetic field can be found with the “right hand rule” ◦ Loop your fingers with thumb pointing out ◦ For straight current, thumb points in direction of current; fingers point in direction of magnetic field ◦ For looped current, fingers point in direction of current; thumb points in direction of magnetic field inside the coil (towards North).
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A long coil of wire consisting of many loops is called a solenoid. When current flows through the coil, a magnetic field is created. We call this an electromagnet. The electromagnet can be made stronger by increasing the current, the number of loops, or adding an iron core.
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A galvanometer measures very small currents (like small-scale ammeter) Can also be used as a voltmeter if connected in series with a resistor Uses a coil inside a magnetic field that rotates when current flows.
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Compass Electric motors and generators Old TV’s and computer monitors - Cathode Ray Tubes (CRT) Electromagnets to lift and move metals Data storage devices – hard disk drives, cassette tapes Planetary magnetic field protects us from solar wind Particle acceleration (Large Hadron Collider)
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A current inside a magnetic field causes coil to spin.
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Reverse process of an electric motor. Uses a spinning coil inside a magnetic field (or a spinning magnet) to generate a current in the coil.
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Read Chapter 24 Page 664 #32-35, 59-63, 73-80 Optional advanced reading: OpenStax Chapter 22
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