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Magnetic Fields & Magnetic Field Strength We have seen that magnets can exert a force on objects without touching them. For this reason we speak of a.

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Presentation on theme: "Magnetic Fields & Magnetic Field Strength We have seen that magnets can exert a force on objects without touching them. For this reason we speak of a."— Presentation transcript:

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2 Magnetic Fields & Magnetic Field Strength

3 We have seen that magnets can exert a force on objects without touching them. For this reason we speak of a magnetic field around a magnet, in the same way that we speak of an electric field around a charged object.

4 A magnetic field is represented by drawing in "magnetic lines of flux". These are lines drawn so that a tangent at any point will show the direction of the magnetic field. The direction of a line of flux is from the North Pole to the South Pole, outside a magnet, from South to North inside the magnet. (One line of flux may cause many lines of iron filings.)

5 Weber - one magnetic line of flux is called a Weber (Wb) Wilhelm Eduard Weber

6 Magnetic Flux - the entire group of lines of flux about a magnet, or in a region is called the magnetic flux. Symbol is  - phi)

7 Magnetic Field Strength An electric field exerts a straight attractive or repulsive force upon a charged object. A magnetic field will exert a particular force upon a charged moving object. This force is perpendicular to the motion of the charge. The force is proportional to the velocity of the moving charge.

8 Two methods of defining magnetic field strength. in terms of amount of force exerted per unit of moving charge - N/C Use the idea that magnetic field strength is directly related to the concentration of flux lines. i.e. lines of flux per unit of area.

9 where B is measured in Tesla (T)  is measured in Webers (Wb) A is measured in square metres. (m 2 )

10 e.g. In a 25m 2 area on the Earth, there are 1.25 x lines of flux measured. What is the field strength of the Earth's magnetic field? *note this is a constant value


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