Tiêu đề 17 EMI Tutorial Soln.pdf ✅

St. Andrew’s Junior College H2 Physics 17-1 TUTORIAL 17: EMI SOLUTIONS Level 1 Solutions: 1(a) • The magnetic flux density (B) at any pt is defined as the force acting per unit current in a wire of unit length placed at right-angles to the field. Mathly, • Magnetic flux  in an area A (of a magnetic field of flux density B) is defined as the product of the area and the component of the magnetic flux density perpendicular to that area. Mathly,  = BA cos  (1a) : angle between B and the normal to the plane of area A. • Magnetic flux linkage , , by a coil with N turns is defined as the product of the magnetic flux passing through each turn & the number of turns in the coil. ie, (b) Faraday’s law states that the magnitude of the induced e.m.f. in a conductor (or coil) is equal to the rate of change of the magnetic flux linkage (of the conductor/coil). • Mathly, mag of E = dt d(N) = d(NBA cos  ) dt • may use “rate of cutting of magnetic flux linkage” in place of “rate of change of mag flux linkage” especially in situation where an emf is induced in straight conductor (c) Lenz’s Law states that the direction of the induced emf is such that its effects oppose the change which causes it. The induced emf produces effects which opposes the change in the magnetic flux linkage. Consequently, work has to be done to overcome this opposition and energy is conserved. Hence the electrical energy associated with the induced current is derived from the work that is done to overcome the change in magnetic flux. If the effects of the induced emf do not oppose the change in magnetic flux, there will be a gain in energy without any work done. This violates the law of conservation of energy. 2 Max flux occurs when θ = zero Thus, max flux = BA cos 0o = (2.1 x 10-4 ) x (7.0 x 10-5 ) x 1 = 1.47 x 10-8 T Max flux linkage = max flux x number of turns = (1.47 x 10-8 T) x 35 = 5.1 x 10-7 Wb Flux Linkage  = N = NBA cos B = I L sin F