1. Measuring the strength of a Magnetic Field
© D Hoult 2008

2. When current flows through a conductor which is in a magnetic field, it experiences a force, except when the conductor is

3. When current flows through a conductor which is in a magnetic field, it experiences a force, except when the conductor is parallel to the flux lines

4. When current flows through a conductor which is in a magnetic field, it experiences a force, except when the conductor is parallel to the flux lines
The direction of the force is at 90° to both the current and the flux lines

5. When current flows through a conductor which is in a magnetic field, it experiences a force, except when the conductor is parallel to the flux lines
The direction of the force is at 90° to both the current and the flux lines
Fleming’s left hand rule helps to remember the relation between the three directions…

8. Thumb
First finger
Second finger

9. ThuMb
Motion
First finger
Second finger

10. ThuMb
Motion
First finger
Field
Second finger

11. ThuMb
Motion
First finger
Field
SeCond finger
Current

18. Factors affecting the Magnitude of the Force
The force depends on

19. The force depends on
- the current flowing through the conductor, I

20. The force depends on
- the current flowing through the conductor
- the length of conductor in the field

21. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that

22. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that
F a current, I

23. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that
F a current, I
F a length of conductor, L

24. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that
F a current, I
F a length of conductor, L
F = I L × a constant

25. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that
F a current, I
F a length of conductor, L
F = I L × a constant
magnetic field strength or

26. The force depends on
- the current flowing through the conductor
- the length of conductor in the field
Experiments show that
F a current, I
F a length of conductor, L
F = I L × a constant
magnetic field strength or magnetic flux density

27. F = I L B

28. F = I L B
units of B Newtons per Amp per meter, NA-1m-1

29. F = I L B
units of B Newtons per Amp per meter, NA-1m-1
1 NA-1m-1 is called 1 Tesla (1 T)

30. F = I L B
units of B Newtons per Amp per meter NA-1m-1
1 NA-1m-1 is called 1 Tesla (1 T)
The flux density of a magnetic field is

31. F = I L B
units of B Newtons per Amp per meter NA-1m-1
1 NA-1m-1 is called 1 Tesla (1 T)
The flux density of a magnetic field is the force per unit current per unit length acting on a conductor placed at 90° to the field

32. F = I L B
units of B Newtons per Amp per meter NA-1m-1
1 NA-1m-1 is called 1 Tesla (1 T)
The flux density of a magnetic field is the force per unit current per unit length acting on a conductor placed at 90° to the field
F = I L B sin q