1. Field Lines

2. Rules for drawing electric field lines
At every point the direction of the field is tangent to the line
Strength is represented by density
Lines go from positive and to negative

4. Rules for Gravitational Field Lines
The force of gravity is always attractive
The field lines will always point towards the center of a spherical mass and arrive perpendicular to the surface

5. Rules for Magnetic Field Lines
Field lines leave the N-pole, enter the S-pole and continue to form a closed loop inside the magnet
Magnetic Flux : the number of magnetic field lines passing through a particular unit area. Proportional to the magnetic field intensity

6. Questions from Provincial Exam: Draw appropriate lines to describe field near the objects shown

7. Questions from Provincial
Three points are indicated as A, B, C on the diagram. List the letters in order of increasing field strength (weakest first)

8. Questions from Provincial
The diagram shows 3 magnetic poles mapped with iron filings. Identify which two poles are alike. Explain your reasoning.

9. ELECTRICITY and MAGNETISM

10. Rules for Magnetic Interactions
1. Like poles repel each other 2. Unlike poles attract each other 3. The force of attraction varies inversely as the square of the distance between the poles Magnetic Dipole: Magnets always seem to come with a N-pole paired with an S-pole

11. ELECTROMAGNETISM
Electrons produce a magnetic field and a changing magnetic field will cause electrons to move.
Discovered by accident in 1819 by Hans Christian Oersted

12. USES Discovery marked the beginning of modern science and technology:
Radio, television, computers, tape recorders, VCRs, CD players, lasers, electric motors and generators, etc

13. Magnetic Fields
Each point of a current carrying conductor creates a magnetic field around itself
The field lines are a set of concentric closed circles perpendicular to the direction of the current

14. Right-hand rule #1 finding direction of magnetic field lines around a conductor
Grasp a current carrying conductor with a your right hand, thumb lies in the direction of the conventional current (positive flow)
The fingers encircle the conductor in the direction of the magnetic field lines caused by the current

15. Magnetic Fields on a Coil
Field lines are closed loops
Inside the coil, uniformly spaced to represent the uniform nature of the field
Outside, spread out to indicate the weakened field
X’s indicate field lines that go into the page
Dots indicate field lines out of the page

16. Magnetic Fields around a Solenoid
Solenoid: a closely wound helix. The field from a solenoid is stronger and more uniform.
The field lines leave one end of the solenoid, circle around and enter the other end.

17. Right-hand rule #2 finding the N-pole of a coil of wire
Place fingers of right hand along the wire of the coil so that your fingers point in the direction of the current in the coil
Extend your thumb
This will indicate the direction of the field lines as they pass through the coil, and thus the face of the coil that acts as the N-pole

18. INTERACTIONS OF MAGNETIC FIELDS
AMPERE

19. Andre Ampere
1820
Developed mathematical law describing the relationship between the current in a conductor and its resulting magnetic field

20. Current in the same direction
Magnetic fields between the two conductors are in opposite directions
The magnetic fields will apply a force drawing the conductors together

21. Current in opposite directions
Magnetic fields between the two conductors are in the same direction
The magnetic fines of force will repel each other

22. Question from previous provincial
Two long straight current-carrying wires are placed so that they are parallel to one another. The picture shows a cross-section of the 2 wires. Draw a representation of the field lines and draw force vectors showing the direction of the magnetic force on each wire.

23. Questions: Section Review
pg 767 #1 a, b, c

24. The AMPERE The unit of measure of electric current intensity
The amount of current in each of 2 long straight parallel conductors, one meter apart, that will cause a force of 2 x 10-7N to act on each meter of wire.

25. The Motor Force
F =kILB
The force exerted by a magnetic on the magnetic field of a current carrying conductor
magnetic field that acts perpendicular to the conductor (B )
current (I)
length of the conductor inside the field (L)
k is the proportionality constant

26. The Electric Motor
Activity from resource book

27. Electromagnetic Induction

28. Electromagnetics
Core of ferromagnetic material placed inside a solenoid increases the strength of the magnetic field inside the solenoid
3 things affect the strength of the electromagnet: size of current, number of turns of the coil, permeability of the core

29. Strong Electromagnets
Must be super-cooled to the point where the coils become superconductors, and lose their resistance.
MRI, High speed trains, Particle accelerators

30. Ampere and Faraday
1820 Ampere shows that an electric current produces a steady magnetic field
1831 Faraday predicts that a steady magnetic field should produce an electric current

31. Lenz’s Law
An induced electric current flows in a direction that opposes the change that produced it.
Heinrich Friedrich Emil Lenz ( )
Thrusting a pole of a permanent bar magnet through a coil of wire, for example, induces an electric current in the coil; the current in turn sets up a magnetic field around the coil, making it a magnet. Lenz's law indicates the direction of the induced current. Because like magnetic poles repel each other, Lenz's law states that when the north pole of the bar magnet is approaching the coil, the induced current flows in such a way as to make the side of the coil nearest the pole of the bar magnet itself a north pole to oppose the approaching bar magnet. Upon withdrawing the bar magnet from the coil, the induced current reverses itself, and the near side of the coil becomes a south pole to produce an attracting force on the receding bar magnet.