1. Electric Currents and Magnetic Fields

2. History Lodestones were discovered 2000 years ago and were magnetic. They were named after Magnesia which is a region in Greece where they were found. Lodestones were discovered 2000 years ago and were magnetic. They were named after Magnesia which is a region in Greece where they were found. The Chinese used them for navigating ships in the 12th century. We know they contained iron ore which is called magnetite. The Chinese used them for navigating ships in the 12th century. We know they contained iron ore which is called magnetite.

3. Moving Charges Create Magnetic Fields In 1820 a Danish scientist Hans Christian Oersted noticed that a wire containing current would deflect a compass needle. In 1820 a Danish scientist Hans Christian Oersted noticed that a wire containing current would deflect a compass needle.  This indicated the relationship between electricity and magnetism.  Moving charges create a magnetic field.  Current running through a wire will create a magnetic field.  The direction of magnetic field can be determined by the right hand rule.

4. Magnetic field lines Bar MagnetWire with current Bar MagnetWire with current

5. Earth’s Magnetic Field The earth is basically one huge magnet. However, the north and south poles are not located exactly at the locations we call the north and south poles. The earth is basically one huge magnet. However, the north and south poles are not located exactly at the locations we call the north and south poles.

6. Earth’s Magnetic Field Changes? The angle between the geographic (true) North Pole according to the earth’s magnetic field and the magnetic north that compasses point to is called magnetic declination. The angle between the geographic (true) North Pole according to the earth’s magnetic field and the magnetic north that compasses point to is called magnetic declination. Magnetic north has wandered throughout geologic time. More than 20 reversals have been recorded in the orientation of the dipoles in rocks on earth (over 5 billion years!) Magnetic north has wandered throughout geologic time. More than 20 reversals have been recorded in the orientation of the dipoles in rocks on earth (over 5 billion years!)

7. Compasses Align in the direction of the field

8. Magnetic fields created by wires

9. Charged Particles in Magnetic fields Moving charges create a magnetic field. Moving charges create a magnetic field. –When charged particles move through an external magnetic field their magnetic fields interact and the charge experiences a force. –The force the charge experiences is always perpendicular to the charge’s velocity and the external magnetic field.

10. Right Hand Rule Use your right hand: Use your right hand: –The palm of your hand pushes in the direction of the force the charge experiences. –Your outstretched fingers point in the direction of the external magnetic field. –Your thumb points in the direction of the current or the velocity of a negative charge charge moving through the external field.

11. Right Hand Rule for charges entering a magnetic field

12. Right Hand rule is used to determine the direction in which the metal rod is deflected

13. To calculate the force a charge experiences when traveling in an external magnetic field F magnetic = Bvqsinθ F magnetic = Bvqsinθ –F magnetic magnetic force exerted on the charge by the external magnetic field.  Unit - Newtons –q the magnitude of the charge traveling in the magnetic field.  Unit - Coulombs –v the velocity of the charge traveling in the magnetic field  Unit - m/s –B The magnitude the the external magnetic field.  Unit - Tesla  One Tesla is equal to 1 C of charge is moving 1 m/s perpendicular to the external magnetic field and experiencing 1 N of force. sinθ angle between v and B sinθ angle between v and B

14. Degree of force the charge experiences depends on the direction of motion relative to the external magnetic field. Degree of force the charge experiences depends on the direction of motion relative to the external magnetic field. –The force has its maximum value when it is traveling perpendicular to the magnetic field. –The force decreases when the charge moves at angles to the magnetic field. –The charge will experience zero force when it is moving parallel to the magnetic field lines. –When a charge is traveling perpendicular to a uniform magnetic field the particle will make a circular path.

15. Right Hand Rule for current Flowing through a wire.

17. Force exerted on a wire carrying charge perpendicular to an external magnetic field F magnetic = B l I sinθ F magnetic = B l I sinθ –F magnetic Force wire experiences due to the external magnetic field.  Unit – Newtons –B Magnetic Field  Unit – Tesla –l (L) Length of the wire  Unit – meters –I Current in the wire  Unit – amperes –sinθ angle between I and B

18. Devices Utilize Electromagnetism Electromagnets Electromagnets Galvanometer Galvanometer DC Motors DC Motors Generators Generators Transformers Transformers

19. Electromagnets A coil of wire attached to a battery creates a magnetic field inside the coil. A coil of wire attached to a battery creates a magnetic field inside the coil. The overlapping magnetic field lines intensify the field inside the coil. The overlapping magnetic field lines intensify the field inside the coil. If a piece of metal is placed inside the coil, the domains of the metal become aligned with the magnetic field inside the coil and strengthens the field. If a piece of metal is placed inside the coil, the domains of the metal become aligned with the magnetic field inside the coil and strengthens the field. Change the direction of current and you change the direction of the magnetic field. Change the direction of current and you change the direction of the magnetic field.

21. Galvanometers Device that measures current using magnetic force. Device that measures current using magnetic force. –A coil of wire is wrapped around a soft iron core that is mounted on a pivot attached to a needle. –When current is run through the wire the magnetic field created by the current interacts with an external magnetic field. –The degree of deflection is related to the amount of current in the coil.

23. Electric Motors Motors use electricity to create mechanical motion. Motors use electricity to create mechanical motion. –Motors use direct current. –A coil attached to a battery is rotated in the presence of a permanent magnet. –Current flows in opposite directions in the upper and lower part of the loop. –As the current moves through the upper part of the loop it is deflected by the permanent magnetic field. And rotates half a turn. –The direction of current is switched every half rotation by contacts at the end of the shaft which keeps the loop rotating in the same direction.

24. DC Motor

26. http://www.walter- fendt.de/ph14e/electricmotor.htmhttp://www.walter- fendt.de/ph14e/electricmotor.htm

27. Electromagnetic Induction Electric current can create a magnetic field but can a magnetic field create current? Electric current can create a magnetic field but can a magnetic field create current? –British scientist Michael Faraday and American scientist John Henry in 1831 independently discovered the answer is yes. –They found by moving a magnet in and out of a coil of wire electric current is induced. –A changing magnetic field can create current. –The amount of current induced is dependent on:  The rate in which the magnet s moved in and out of the coli of wire.  The number of coils in the wire.

28. Generator Simulation http://www.walter- fendt.de/ph14e/generator_e.htmhttp://www.walter- fendt.de/ph14e/generator_e.htm

29. http://www.physclips.unsw.edu.au/jw/electr icmotors.html#mandghttp://www.physclips.unsw.edu.au/jw/electr icmotors.html#mandg