# Hans Christian Oersted Accidently discovered electric current would

• Slides: 15

Hans Christian Oersted • Accidently discovered electric current would cause a compass needle go haywire. • Discovered that moving Charges (Electric Currents) create Magnetic Fields

Magnetic Field (B-field) • The invisible aura around a magnet Remember: • If a charged particle moves through a magnetic field, it will feel a force from that field • A charged particle will be deflected by a magnetic field.

A current carrying wire • A straight current-carrying wire creates circular magnetic field lines: B I

Right Hand Rule Used to draw and show direction of a magnetic field around a current carrying wire. Right Hand Rule: 1. Thumb of right hand – points in direction of current flow 2. Wrap fingers like you are grabbing the wire 3. Fingers show direction of the magnetic field

Symbols • Magnetic Field (B-Field) • “Bullets” – out of page • “Feathers” – into page Example: I

Wire in a Loop • If wire is bent into a loop, the B-field lines become bunched up inside the loop I

Explained • There is a greater concentration of feathers inside the loop than bullets on the outside of the loop, therefore the B-field is stronger inside the loop. • Bend wire into another loop, the concentration of the B-field doubles, and so on. • The direction of the B-field depends on the direction of current flow in the wire.

Solenoid • A coil of wire • You can magnetize a solenoid by running electric current through it. • A Solenoid can be used to move a piece of ferromagnetic material and do physical work like opening car doors! B I

Electromagnet • A Solenoid can become an Electromagnet by placing a ferromagnetic core in the coil Examples of Electromagnets • MRI - magnetic resonance imaging • Maglev – fast moving transportation, magnetically levitated I

TV’s • Old TVs are big and boxy. The box part holds a cathode ray tube that basically shoots electrons at the screen lined with a phosphorescent substance on the TV. • Without an electromagnet (steering coil), those electrons would hit the screen in only one location. – These copper coils create a magnetic fields inside the tube, and the electron beam responds to the fields. – One set of coils creates a magnetic field that moves the electron beam vertically, while another set moves the beam horizontally. – By controlling the voltages in the coils, you can position the electron beam at any point on the screen

• Human body – contains billions of atoms. • For the MRI scan only concerned with the hydrogen atom (very abundant since the body is mostly made up of water and fat) • Hydrogen atoms have a strong magnetic moment, which means that in a magnetic field, they line up in the direction of the field.

Force of the magnetic field • Two magnets will apply a force on each other. • Therefore if you have a moving electric charge (which has a magnetic field around it) it can be forced to move by another magnetic field F=qv. B Fm = Force (Newtons) q = Charge (Coulombs) v = Velocity (m / s) B = Magnetic Field (Tesla) Many moving charges: called electic current F=BIl Fm = Force (Newtons) B = Magnetic Field (Tesla) I = Current (Amps) l = length (meters) A charge will feel the greatest force when it is moving PERPENDICULAR to the B-field. It will feel no force if it is moving PARALLEL to the B-field.

Physics Gang Signs To determine the direction of the above variables you will need to know the “Physics gang signs” Thumb represents force Pointer finger represents direction of velocity All other fingers represent the B-field, where your knuckles are at the North Pole.

Example If an electron in an electron beam experiences a downward force of 2 E – 14 N while traveling in a magnetic field of 8. 3 E – 3 T directed to the west. Find the DIRECTION and MAGNITUDE of the velocity of the electron.