Two solenoids are used to produce a magnetic field across a cathode-ray tube (Fi

Question

Two solenoids are used to produce a magnetic field across a cathode-ray tube (Figure 28.39 pg 920). Each coil has N=6000 turns, is L=0.09m long, has radius r=0.06m, and carries current I=1.2A. The CRT is d=0.07m in diameter.

(a) Find what field would be in the CRT if it as inside an infinite solenoid with the same radius and turns per length as the these solenoids.
Binfinite = ___ T

(b) Find the field at the center of the CRT.
Bcenter = ___ T

(c) Find the field at a point on the edge of the CRT along the central aixs of the solenoids.
Bedge = ___ T

Explanation / Answer

MAGNETIC FIELD(B) of a solonoid is given by the formula B = 0 nI.

MAGNETIC FIELD FOR A TOROID IS given by B =0 NI/2r

n = no. of turns per unit lenght= N/l

MAGNETIC FIELD for each solonoid is given by B = (4*10^-7)* (6000/0.09)*(1.2) = 0.10048 T.

a) MAGNETIC FIELD at the centre of crt TUBE(TOROID) B = ((4*10^-7) *6000* 1.2)/2*0.035

                                                            B = 0.04114 T

b) since current enclosed by the loop is zero, magnetic field at the edge of crt tube will zero.

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