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
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 :
- 天同Lv 75 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.