 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.

 Fuse Box or Circuit Breaker?  GFCI’s?

Chapter 24

 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

 A ferromagnet is a magnet made of a ferromagnetic metal, such as iron, cobalt, or nickel.  Created inside a magnetic field.

 Splitting a magnet creates smaller magnets that each have a north pole and south pole.

 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

 Earth’s magnetic field: ~4x10 -5 T

 How do we know that Earth’s magnetic field has changed direction?

 You have the rest of class to work on:  Check your answers to Chapter bookwork  Chapter 22 Review  Chapter 23 Review

 Moving charges produce magnetic fields.  Magnetic fields affect moving charges.

 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)

 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

 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

 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? 3.2x N

 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? 4.3x N

 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).

 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.

 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.

 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)

 A current inside a magnetic field causes coil to spin.

 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.

 Read Chapter 24  Page 664 #32-35, 59-63,  Optional advanced reading: OpenStax Chapter 22