1. electromagnetic induction
2. Electromagnetism and
electromagnetic induction
Magnetic flux
Flux density
mmf
Field strength (H) & Permeability
B/H curves
Faraday’s Law
Faraday‘s law of Electromagnetic Induction
Lenz’s Law
Fleming’s Left-hand and Right-hand Rules
2.10 Self-inductance
2.11 Energy stored

2. Magnetic field is invisible-observed by using paper and iron fillings.
2.1 Magnetic flux
Magnetic field is invisible-observed by using paper and iron fillings.

3. Line of magnetic flux (lines of magnetic force).
North-seeking pole or N-pole points towards north.
South-seeking pole or S-pole points towards south.

4. Magnetic field patterns :
Unlike poles-Attraction
Like poles-Repulsion

5. Characteristic of lines of magnetic flux
Line of magnetic flux - direction, closed loop
Shorten lines of magnetic flux (unlike poles attract each other)
Parallel in same direction repel one another (like poles repel each other)

6. Magnetic Flux
Number of lines of magnetic force coming out or entering into a magnetic surface.
Symbol:  Unit: weber (Wb)

7. 2.2 Flux density
magnetic flux entering unit area normally (at right angle) is the magnetic flux density
Symbol: B Unit: tesla (T)
Flux density B= /A tesla (T)

8. 2.3 mmf (magnetomotive force)
The force - produces the magnetic field
F = I*N ampere turn
Symbol: F Unit : AT

9. 2.4 Field strength (H) & Permeability Field Strength
magnetic field intensity - m.m.f. per unit length of the magnetic circuit.
Magnetic intensity = F/l = IN/l
Symbol: H Unit: ampere per metre
known as magnetizing force OR magnetic field strength

10. Magnetic field is concentrated in the iron rod.
Brass rod has little effect on the magnetic field.

11. Iron has a lower “magnetic resistance” than that of the surrounding air path.
Magnetic resistance of the brass has much the same value of the surround air.
Every material has particular value of conductivity known as magnetic permeability.
Flux Density = absolute permeability x magnetic field intensity
B = H
Symbol:  Unit: T/(A/m) OR H/m

12. Permeability of Free Space
magnetic space constant - permeability of vacuum or of air.
symbol: o Unit: T/(A/m) Or H/mm
value: 4xx10-7 H/m
Relative and Absolute Permeability
Absolute permeability = o x relative permeability  = o x r
where r = relative permeability
symbol: r unit: none

13. Ferromagnetic materials
e.g. iron, steel, nickel and cobalt
Paramagnetic materials
r 1
i.e. material become weakly magnetized in the direction of the magnetising field.
e.g. aluminium, chromium

14. Diamagnetic materials
e.g. gold, silver.

15. 2.5 B/H curves
Magnetization characteristics of soft magnetic materials
Flux density increases rapidly due to alignment of a large number of magnetic domains
Knee point –further increase of H causes very little change in magnetic field.
magnetic saturation - all domains aligned with the magnetic field.
Magnetic field intensity H
B Flux density
Fig. 6

17. 2.6 Faraday’s Law

19. an e.m.f. is induced in the conductor whenever it cuts line of magnetic flux.
Conductor move upwards or downwards - induced e.m.f. is zero.
Conductor’s velocity will affect the magnitude of the induced e.m.f.

20. Electromagnetic Induction
2.7 Faraday’s law of
Electromagnetic Induction
Magnetic field linking with the conductor changes - e.m.f. is induced.
Induced e.m.f.’s magnitude rate of change of the magnetic flux linking with the conductor.

21. 2.8 Lenz’s Law
The e.m.f. induced - circulate current in a direction opposes the change of magnetic flux inducing the e.m.f.

22. 2.9 Fleming’s left and Right-
hand Rules
Fleming’s right-hand rule

23. Fleming’s left-hand rule

24. 2.10 Self-inductance
Conductor carrying current is surrounded by magnetic field.
Conductor current  , magnetic field  .
By Lenz‘s Law,  in flux  e.m.f. to be induced in conductor opposes the change in flux (change in current).
This e.m.f. is Self-induced e.m.f. (self-inductance)

25. Self-inductance of 1 henry (H) if - e. m. f
Self-inductance of 1 henry (H) if - e.m.f. of 1 volt (V) is induced when current changes at 1 ampere per second (A/s).

26. 2.11 Energy Stored In a circuit of inductance L henrys.
Current increases at a uniform rate from zero to I amperes in t seconds.
Average current in the circuit is I/2 amperes,
Average value of induced e.m.f. is
L*(rate of change of current)=LI/t
The average energy consumed by the inductance is therefore:
W = Eit =