TOPIC3 ELECTROMAGNETIC FIELD4.doc - Topic 3 Electromagnetic Field 3.0 ELECTROMAGNETIC FIELD Explain Maxwell’s equations and Lorentz Force equation

# TOPIC3 ELECTROMAGNETIC FIELD4.doc - Topic 3 Electromagnetic...

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Topic 3: Electromagnetic Field 3.0: ELECTROMAGNETIC FIELD Explain Maxwell’s equations and Lorentz Force equation Produce Maxwell’s equation Produce Lorentz Force equation Apply Maxwell’s and Lorentz Force equation in various applications related to electromagnetic field Investigate Faraday’s Law of Induction State the Faraday’s Law of induction Identify the significant of Faraday’s Law of Induction. Apply Faraday’s Law in various applications ____________________________________________________ 3.1 Introduction to magnetic fields We have seen that a charged object produces an electric field E at all points in space. In a similar manner, a bar magnet is a source of a magnetic field B . This can be readily demonstrated by moving a compass near the magnet. The compass needle will line up along the direction of the magnetic field produced by the magnet, as depicted in Figure 3.1. Figure 3.1 Magnetic field produced by a bar magnet Notice that the bar magnet consists of two poles, which are designated as the north (N) and the south (S). Magnetic fields are strongest at the poles. The magnetic field lines leave from the North Pole and enter the South Pole. When holding two bar magnets close to each other, the like poles will repel each other while the opposite poles attract as shown in Figure 3.2. Figure 3.2 Magnets attracting and repelling Unlike electric charges which can be isolated, the two magnetic poles always come in a pair. When we break the bar magnet, two new bar magnets are obtained, each with a Prepared by Engr. Sabariah Bt Hj Bohanudin Page 1
Topic 3: Electromagnetic Field North Pole and a South Pole as depicted in Figure 3.3. In other words, magnetic “monopoles” do not exist in isolation, although they are of theoretical interest. Figure 3.3 Magnetic monopoles do not exist in isolation How do we define the magnetic field B ? In the case of an electric field E , we have already seen that the field is defined as the force per unit charge: q F E e ….(3.1) However, due to the absence of magnetic monopoles, B must be defined in a different way. 3.2 The Definition of a Magnetic Field Magnetic field at a point can be defined by considering a particle of charge q and moving at a velocity v . Experimentally we have the following observations: 1. The magnitude of the magnetic force B exerted on the charged particle is proportional to both velocity, v and charge, q . 2. The magnitude and direction of magnetic force, B F depends on v and B . 3. The magnetic force B F vanishes when v is parallel to B . However, when v makes an angle with B , the direction of B F is perpendicular to the plane formed by v and B , and the magnitude of B F is proportional to sin . 4. When the sign of the charge of the particle is switched from positive to negative (or vice versa), the direction of the magnetic force also reverses.

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