Magnets and Magnetic Fields Magnetism Magnets and Magnetic Fields

Magnets Magnets – objects, usually metallic, that can attract or repel certain other objects, such as iron Have two poles: North and South (or North-seeking and South-seeking) Will point toward the Earth’s magnetic poles North points toward Earth’s Magnetic South Pole and South points Earth’s Magnetic North Pole Like poles repel and opposite poles attract No matter how many times you cut a magnet, it will always have both a North and South pole Used in multiple applications – electromagnets, motors, recording devices, maglev trains Earth acts like a giant magnet

Magnetic Domains Moving charges cause magnetic fields Every electron or proton is constantly in motion Always generating a magnetic field Most charged particles cancel each other out Some substances have the charges moving in such a way that the magnetic fields line up Ferromagnetic – includes iron, cobalt, and nickel Can be effected by a magnet In ferromagnetic materials, the charges group together in large groups called magnetic domains Most of the time, the domains are oriented randomly – nonmagnetic In natural magnets or in substances effected by a magnet, the domains are oriented more closely Aligned magnetic domains enhance the magnetic field

Magnetic Domains

Magnetic Domains Substances can be made into permanent magnets Prolonged exposure to a permanent magnet can cause ferromagnetic materials to become magnetic Stroking iron with a magnet Being near a magnet for a long enough time – induced magnetism Magnetically soft materials are easy to magnetize, but lose their magnetism easily Magnetically hard materials do not magnetize easily, but will keep their magnetism longer To break a magnet, expose it to heat and cold or hammer it

Magnetic Fields Magnetic field – a region in which a magnetic force can be detected Surrounds any magnetized material, including Earth Earth’s magnetic field shields us from ultraviolet radiation, x-rays, gamma rays, and the solar wind from space and traps the atmosphere close to the surface Magnetic fields run from the North Pole to the South Pole of a magnet Can be drawn similar to electric field lines The more lines, the stronger the field Magnets are stronger at the poles

Magnetic Fields Magnetic Flux – the number of magnetic field lines that cross a certain area at right angles to that area Symbol is ΦM Magnetic flux = surface area * magnetic field component normal to the plane of surface ΦM = A * B * cosθ A = surface area (meters squared, M2) B = Magnetic Field Strength (Teslas, T) θ = angle between perpendicular and the magnetic field , usually going to be 0.0° at our level

Magnetic Field of a Bar Magnet Section 1 Magnets and Magnetic Fields Chapter 19 Magnetic Field of a Bar Magnet

Magnetic Fields Earth’s magnetic field is currently oriented so that magnetic south is in the geographic north and magnetic north is located in geographic south The magnetic field reverses itself periodically Can be observed at sea-floor spreading areas Magnetic declination – the difference between true north (as defined by the Earth’s axis of rotation) and the North Pole of a compass Varies everywhere on Earth Essentially zero in the center of North America 20° East of true North in the State of Washington Source of Earth’s magnetic field is believed to be convection currents in the molten core of the Earth As the molten metal moves, it induces a magnetic field Stronger planetary magnetic fields may cause a faster planetary rotation

Earth’s Magnetic Field Section 1 Magnets and Magnetic Fields Chapter 19 Earth’s Magnetic Field