1. Magnetic Forces

2. * Current-carrying wires have magnetic fields and… * Magnets exert forces on other magnets. Therefore… Magnets exert forces on current-carrying wires. The magnitude of the magnetic force is given by F = iL x B Where B is the magnetic field, measured in Tesla, T i is the current, measured in amps L is the length of the wire, measured in meters. The current flowing through the wire and the magnetic field, B, must be perpendicular to each other. Only PERPENDICULAR components contribute to the magnetic force! Yes, we’re back to vector components! The Force on a Current-Carrying Wire in a Magnetic Field

3. SpeakerSpeaker and Magnets 1. There is a magnet in the back of most speakers. 2. The wires going into the back of a speaker carry current from the amplifier. 3. The coil of wire experiences a magnetic force which pushes it back a forth against the paper cone. 4. The cone vibrates producing sound.

4. James Clerk Maxwell Maxwell showed that electricity and magnetism were all part of the same phenomenon- the electromagnetic force! He wrote 4 very famous equations showing that relationship and describing electromagnetic waves

5. Maxwell’s four equations: Don’t these look like fun?

6. The Direction of the Magnetic Force, F = iL x B Force is a vector and always has a direction associated with it. The direction of the magnetic force is determined by a “right- hand rule” 1.Point your thumb in the direction the current is flowing. 2.Point your fingers in the direction of the magnetic field. 3.Your palm will face the direction of the magnetic force on the wire.

7. A wire of length 2.0 meters carries a current of 1.2 A and is at an angle of 30 degrees to a magnetic field of 0.008 T as shown above. What is the magnetic force on the wire? What is the direction of the force? F = iL x B = F = (1.2 A)(2.0 m) x 0.008 T sin 30˚ F = 0.0096 N Direction: use the right-hand rule… “perpendicular and down into the page”

8. Magnetic Fields created by current carrying wires If two parallel wires have currents traveling in opposite directions, the magnetic fields generated by those currents cause these wires to repel each other. However, if two parallel wires have currents traveling in the same direction, the magnetic fields generated by those currents between the wires results in the wires attracting each other. i, current F, force i, current F, force

10. The Force on a Moving Charge in a Magnetic Field Just as current-carrying wires (a stream of moving charges) experience a force in a magnetic field, a single electrical charge also experiences a force if it is moving in a magnetic field. e-e- Magnetic force

11. The Force on a Moving Charge in a Magnetic Field The magnitude of the force is given by F = qv x B Where B is the magnetic field in Tesla, q is the electric charge in Coulombs v is the velocity in meters per second Only perpendicular components of v and B contribute to the magnetic force.

12. CRT’s and Magnets (TV and computer monitors- NOT flat screen) 1. Electrons are produced at the cathode. 2. They move through an electromagnet. 3. The electromagnet pushes them in different direction. 4. The hit the phosphorescent screen, making it glow.

13. How the Earth’s Magnetic Field the MAGNETOSPHERE, protects us from moving charges…

14. There are storms on the surface of the sun that are known as solar flares or sun spots. These storms eject electrons, ions, and atoms out through the corona toward space. This is called the “solar wind” or “cosmic radiation”.

15. Earth’s Magnetic Field The Magnetosphere acts like a shield around the Earth to protect us from the solar wind. Most of the solar wind is deflected around the Earth and moves out toward the outer solar system.

16. When the solar wind is particularly intense, some of these charged particles penetrate the Earth’s Magnetosphere.

17. These charged particles gets trapped in Earth’s magnetic field lines, experiencing the magnetic force that causes them to orbit around and around the field lines and travel from pole to pole. They can cause disruption of signal from satellites and can even cause the destruction of sensitive equipment inside satellites.

18. But… it also can cause the atmospheric molecules near the field lines to glow. This causes the auroras: Aurora Borealis, the Northern lights Aurora Australis, the Southern lights.

22. Particle Accelerators This magnetic force is used to accelerate particles in laboratories like CERN, in Switzerland, to study fundamental particles and their interactions in its Large Hadron Collider.

23. The magnetic force on a moving charge will be a centripetal force, causing the charge to move in a circular pathway. Magnetic Force = centripetal Force qv x B = mv 2 / r The direction of the Force is given by the right-hand rule: Thumb = direction of v (velocity) Fingers = B (magnetic field) Palm = Force on a POSITIVE charge

24. Mass Spectrometer A mass spectrometer is a machine that can determine the mass of a subatomic charged particle by measuring the radius of the circle it moves in while under the influence of a magnetic field.

25. How a Mass Spectrometer works First, charges are accelerated down a tube by applying a potential difference,  V. The work done on the charge, q  V, transforms into kinetic energy: q  V = ½ mv 2 Next, the moving charge enters a known magnetic field, where the magnetic force causes circular motion. Measuring the circle’s radius provides the info needed to determine the mass of the charge.