MAGNETISM Percorso CLIL V B Linguistico Prof.sse M.Castracane e M.V.De Nigris a.s. 2014/2015

The metals affected by magnetism consist of tiny regions called 'Domains' which behave like tiny magnets.

Magnetic fields Magnetic fields are areas around a magnet where there is a magnetic force. You can investigate these using a plotting compass or iron filings. Like poles repel and unlike poles attract.

Unlike poles attract. North and South. Like poles repel. North and north. South and south

Field lines run from North to South. The magnetic field is strongest at the poles.

The Earth itself has a huge magnetic field - as if it had a huge bar magnet embedded at its centre. The Earth’s magnetic field lines emerge from near the geographical north pole and re-enter it at the south pole.

Angle of Declination Difference between true north and magnetic north

Now show them our compasses

Hans Christian Oersted (1777-1851) Oersted’s Experiment Hans Christian Oersted (1777-1851) Hans Christian Oersted discovered in 1820 that an electric current near a compass causes the compass needle to be deflected. Oersted's experiment showed that every electric current has a magnetic field surrounding it.

Oersted’s Experiment According to the right-hand rule, the electron current in a wire and the magnetic field it generates are perpendicular to each other.

Oersted’s Experiment All magnetic fields originate from moving electric charges. A magnetic field appears only when relative motion is present between an electric charge and an observer. Electric and magnetic fields are different aspects of a single electromagnetic field.

Solenoids Solenoids are one of the most common electromagnets. Solenoids consist of a tightly wrapped coil of wire, sometimes around an iron core. The multiple loops and the iron magnify the effect of the single loop electromagnet. A solenoid behaves as just like a simple bar magnet but only when current is flowing. The greater the current and the more turns per unit length, the greater the field inside. An ideal solenoid has a perfectly uniform magnetic field inside and zero field outside.

Electromagnets: Straight Wire Permanent magnets aren’t the only things that produce magnetic fields. Moving charges themselves produce magnetic fields. We just saw that a current carrying wire feels a force when inside an external magnetic field. It also produces its own magnetic field. A long straight wire produces circular field lines centered on the wire. To find the direction of the field, we use another right hand rule: point your thumb in the direction of the current; the way your fingers of your right hand wrap is the direction of the magnetic field. B diminishes with distance from the wire. The pics at the right show cross sections of a current carrying wire. I out of page, B counterclockwise I into page, B clockwise I  B

Electromagnets A wire with a current in it, has a magnetic field around it. The strength of a magnetic field can be increased by wrapping a wire around an iron bar

Electromagnet A soft iron rod has no magnetic field When current flows in the wire the soft iron becomes magnetised so a magnetic field is detected by the plotting compasses.

Notice the compasses point at right angles to the current

The Earth’s magnetic field extends far into space The Earth’s magnetic field extends far into space. It is called the “magnetosphere.” The solar wind is constantly bombarding the Earth’s magnetic field. Sometimes these charged particles penetrate that field. These particles are found in two large regions known as the Van Allen Belts. When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…

When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called… The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere