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_ Answers Week 10 I Mechanical System: (i) Pull mass to A, store potential energy %k A2 . (ii) Release mass, it will reduce its potential energy until x = 0, when all the energy is kinetic.
(iii) It will use its kinetic energy to go to x = —A where Energy is again all
I k potential. Hence oscillation occurs with x = A Coswt, , a) = E 2 .
Electrical System: (i) Charge capacitor, store energy—jg; my: ﬁeld. (ii) Open S], close 82. Capacitor sets up current in L, E - ﬁeld in C collapses all the energy is in '
theﬁ ﬁeld in L. (iii) Current through L recharges C until 13 —> 0. Hence, charge oscillation occurs q =QCosa2t, a) =——1—.— m (i) If current increases by a factor of 2, X is a capacitor
because i0 = a," W C Cos cut .. . . . 6'
(11) If current reduces by a factor of 2, X 18 an inductor because to = — 'WmL Cos cot . (155 —163)V
C=5.31x10‘8F Power PW (t) = i(t) 30‘) = im 6‘," [SinzwtCosgﬁ + Sincot Cos cotSind] . 2 2
1m am .9 8
(w) 2 o¢ 22015 m ¢ R
Because Cosgb = E Conduction Current: FLUX OF CHARGE IN A CONDUCTOR IC .= me e A VD .
Displacement CurrentpRATE OF CHANGE OF FLUX OF E as a function of q a A 4‘
time zD=a in ”At ...
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- Fall '11