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  1. 圖片參考:http://i212.photobucket.com/albums/cc82/doraemonpaul/yahooknowledge/ magnetism /squareloop9.jpg 參考資料: my physics knowledge + my maths...

  2. The meaning is that AC can be stepped up before long distance transmission. not step up during transmission for long distance. The reason is that varying current can induce e-field that allow stepping up in the transformer, the e-field can change the voltage by the ratio of...

  3. 1. Statement 1 is wrong as the magnetic field produced by coil Y needs to oppose that on coil X, the induced current direction in Y should be opposite to that of X, i.e. anticlockwise. 2. When the magnetic approaches the coil, the end of...

  4. Q: Why we cannot use Hall probe in this experiment? If a Hall probe is used , what is the drawback? A: A Hall probe can only be used to measure the magnetic flux of a static magnetic field. Since ac is...

  5. Since the loops are identical, their magnetic flux densities should have the same magnitude, say B' With them placed perp. to each other, the resultant magnetic flux density is given by: B = B'√2 by...

  6. This is a force-magnetic inducing a current. Hence, we use Fleming's right hand rule. For the magnetic field pointing in the paper, the induced current flows clockwisely, the force should be downward. Hence, it is D...

  7. Case I: When r <= R (i.e. the point is inside the ring OR on the circumference) 圖片參考:http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM1.jpg 圖片參考:http://i117.photobucket.com/albums/o61/billy...

  8. 1. Distance of X from each wire = 25/(2.sin(45) cm = 17.68 cm = 0.1768 m Magnetic flux density at X from each wire = (uo).(2.5)/(2.pi x 0.1768) T = 2.828x10^-6 T where (uo) is the permeability of free space (= 4.pi x 10^-7 H/m) Hence, resultant magnetic flux density = square...

  9. 1.(a) Induced emf = (4x10^-5) x 10 x 0.2 v = 8 x 10^-5 v (b) The wire is placed in the eas-west direction and the earth's horizontal component of the magnetic field is in the south-north direction, hence the east end of the wire is +ve. 2. (a) Magnetic field intensity = 120...

  10. 1. By right-hand-grip rule, the magnetic field at B should point into the paper. Magnetic field due to the two long straight wires, B' = 2 X u0I/4pir = u0I/2pir Magnetic field due to the semi-circular arc, B" = u0I/2r So, the...