(II) The betatron, a device used to accelerate electrons to high energy, consists of a circular vacuum tube placed in a magnetic field (Fig. 29–48), into which electrons are injected. The electromagnet produces a field that (1) keeps the electrons in their circular orbit inside the tube, and (2) increases the speed of the electrons when B changes. ( a ) Explain how the electrons are accelerated. (See Fig. 29–48.) ( b ) In what directions are the electrons moving in Fig. 29–48 (give directions as if looking down from above)? ( c ) Should B increase or decrease to accelerate the electrons? ( d ) The magnetic field is actually 60 Hz ac; show that the electrons can be accelerated only during 1 4 of a cycle ( 1 240 s ) . (During this time they make hundreds of thousands of revolutions and acquire very high energy.)
(II) The betatron, a device used to accelerate electrons to high energy, consists of a circular vacuum tube placed in a magnetic field (Fig. 29–48), into which electrons are injected. The electromagnet produces a field that (1) keeps the electrons in their circular orbit inside the tube, and (2) increases the speed of the electrons when B changes. ( a ) Explain how the electrons are accelerated. (See Fig. 29–48.) ( b ) In what directions are the electrons moving in Fig. 29–48 (give directions as if looking down from above)? ( c ) Should B increase or decrease to accelerate the electrons? ( d ) The magnetic field is actually 60 Hz ac; show that the electrons can be accelerated only during 1 4 of a cycle ( 1 240 s ) . (During this time they make hundreds of thousands of revolutions and acquire very high energy.)
(II) The betatron, a device used to accelerate electrons to high energy, consists of a circular vacuum tube placed in a magnetic field (Fig. 29–48), into which electrons are injected. The electromagnet produces a field that (1) keeps the electrons in their circular orbit inside the tube, and (2) increases the speed of the electrons when B changes. (a) Explain how the electrons are accelerated. (See Fig. 29–48.) (b) In what directions are the electrons moving in Fig. 29–48 (give directions as if looking down from above)? (c) Should B increase or decrease to accelerate the electrons? (d) The magnetic field is actually 60 Hz ac; show that the electrons can be accelerated only during
1
4
of a cycle
(
1
240
s
)
. (During this time they make hundreds of thousands of revolutions and acquire very high energy.)
Interaction between an electric field and a magnetic field.
] Two very long parallel conductors carry equal current along the
same direction. Increasing the distance between them by a factor of 3
and decreasing both currents equally by a factor of 1/7 will change the
magnitude of the original magnetic force per unit length between the two
by a factor that is most nearly
(A) 7²/3.
(B) 7/3².
(C) 1/(7²-3).
(D) 1/(7-3).
(E) 3/7².
An electron enters a uniform magnetic field B = 0.23 T at
a 45° angle to B. Determine the radius r and pitch p (distance
between loops) of the electron's helical path assuming its
speed is 3.0 × 10° m/s.
See Fig. 20–68.
В
-2r.
FIGURE 20-68
В
Problem 79.
Physics for Scientists and Engineers: A Strategic Approach, Vol. 1 (Chs 1-21) (4th Edition)
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