Ls 發問於 科學及數學物理學 · 5 年前

Magnetism question plz help?

The following are typical data for experiments on a magnetic field B produced by current I:

Long wire r=3cm,

Circular coil N=50 R=5cm

Solenoid n=100m^-1

a)If I = 1A, find B for each case.

b)Hence explain why a 5kHz a.c. is used in Fig 21.13

Figure 21.13 :

http://i613.photobucket.com/albums/tt212/Yan_Wa_Ch...

1 個解答

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  • 天同
    Lv 7
    5 年前
    最愛解答

    (a) Long wire: B = (uo)I/(2.pi.r)

    where uo is the permeability of free space (= 4.pi x 10^-7 F/m)

    and pi = 3.14159...

    hence, B = (4.pi x 10^-7) x 1/(2.pi x 0.03) T = 6.67 x10^-6 T

    Circular coil: B = (uo)N.I/2R

    hence, B = (4.pi x 10^-7) x 50 x 1/(2 x 0.05) T = 6.28 x 10^-4 T

    Solenoid: B = (uo).n.I

    hence, B = (4.pi x 10^-7) x 100 x 1 T = 1.26 x 10^-4 T

    (b) The use of 5 kHz ac is to produce current in the search coil by electromagnetic induction.

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