Fig. 3.69.(a)
(b)Fig. 3.68.3.251. Find the magnitude and direction of a force vector acting
on a unit length of a thin wire, carrying a current I = 8.0 A, at
a point 0, if the wire is bent as shown in
(a) Fig. 3.68a, with curvature radius R = 10 cm;
(b) Fig. 3.68b, the distance between the long parallel segments
of the wire being equal to 1 = 20 cm.
3.252. A coil carrying a current I = 10 mA is placed in a uniform
magnetic field so that its axis coincides with the field direction.
The single-layer winding of the coil is made of copper wire with
diameter d = 0.10 mm, radius of turns is equal to R = 30 mm.
At what value of the induction of the external magnetic field can
the coil winding be ruptured?
3.253. A copper wire with cross-sectional area S = 2.5 mm 2
bent to make three sides of a square can turn about a horizontal
axis 00' (Fig. 3.69). The wire is located in uniform vertical magnetic
field. Find the magnetic induction if on passing a current I = 16 A
through the wire the latter deflects by an angle 0 = 20°.
3.254. A small coil C with N = 200 turns is mounted on one
end of a balance beam and introduced between the poles of an electro-
magnet as shown in Fig. 3.70. The cross-sectional area of the coil
Fig. 3.70,is S = 1.0 cm 2 , the length of the arm OA of the balance beam is
1 = 30 cm. When there is no current in the coil the balance is hi
equilibrium. On passing a current I = 22 mA through the coil the
equilibrium is restored by putting the additional counterweight of141