What would be the advan*w.j esw+9;bfdpmvs +tage, in Faraday’s experiments (Fig. Below), of using coi+ .m+s9wjwsdvfbe; p *ls with many turns?

What is the difference vqc ,i2d,rer 1between magnetic flux and magnetic field?

Suppose you are holding a circular ring of wire and suddenly thrusck-i *2i)n/ut:6( gbxr+/g fklsc i wat a magnet, south pole first, away from you toward the center of the circle. Is a current induced in the wire? Is a current induced when the magnet is held steady within the ring? Is a current induced when yoxuitgicn a sgw/ i6-(2bc *kr+):fkl/u withdraw the magnet? In each case, if your answer is yes, specify the direction.

Two loops of wire are moving in the vicinity of a very long straight wijd)d4 5w;c80yuar b ne;r5uqq re carrying a steady current as shown in (Fig. Below). Find the direction o0qa5; dq rd;w ru 5n)bjc4eyu8f the induced current in each loop.

Suppose you are looking along a line through the wn1 h7ati.a tpqf: )x3centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connect xipw3qf.ah7n1t:t a)ed to the front loop, establishing a clockwise current.
(a) Will a current be induced in the second loop?
(b) If so, when does this current start?
(c) When does it stop?
(d) In what direction is this current?
(e) Is there a force between the two loops?
(f) If so, in what direction?

  In (Fig. Below), determine the dghh7sew 1e4w1irection of the induced current in resistor $R_A$ when
(a) coil B is moved toward coil A, ----待选择----increasedecrease 
(b) when coil B is moved away from A, ----待选择----increasedecrease 
(c) when the resistance $R_B$ is increased. ----待选择----increasedecrease 

In situations where a small signal must travel over a distance, a “shieldh xzq9l+tg0ex 2 ur-/red cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return /t9qzx02-hlr + uxr gecurrent. Why is a “shield” necessary?

What is the advantage of placing the two insulated electric 4 u6 u*wlh1q+nu qq6rsst(3o0w 8i cpuwires carrying ac close together or eucutu4l on+ rw 8qqq(0i3 *6shwps1u6 ven twisted about each other?

Explain why, exactly, the lights may dij; rl3-lpxd q8m briefly when a refrigerator motor starts up3jlrlq x8-d;p. When an electric heater is turned on, the lights may stay dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hand rules to shlqo: ,3p, (m0x)yj5 jbzwps ymow why the counter torque in:q z)b5yyom 0lj p(,,js wxpm3 a generator opposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper or aluminum wheel, or j tvjg8zf h 89, (o/d4zwpqwl+must the wwqzfp +lj(gd oz /j,9vh4t8w8heel be ferromagnetic? Explain.

It has been proposed that eddy c0:me cpib* :zkx4ov/7lct:lz urrents be used to help sort solid waste for recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to slide down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmet pkb0 mzx4o/*itlc ::cvzl:7 eallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quic8kmlz .ud3y1 dkly through a magnetic field th 3 dkml8zyd.1uan does a solid bar. Explain.

If an aluminum sheet is held beto u.4m5 k.w5hla b v4/yvp4epsween the poles of a large bar magnet, it requires some force to pull it out of the magnetic field even though e44 u5mb vvko4ap /.wh.sl5ypthe sheet is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling insides8on -krb 4ky.rks/k26( lvhp a vertical metal tube reaches a terminal velocity ev6h vns- k.8 4rlkpsb(/o2k kryen if the tube is evacuated so that there is no air resistance. Explain.

A metal bar, pivoted at 1qpize f.72zx one end, oscillates freely in the absence of a magnetic field; but in a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical devic2 7q ex.pzz1ifes.)

An enclosed transformer riy t 0/p qbr8m+icm,6has four wire leads coming from it. How could you determine the ratio of turns on the two coils without taking the transformer apart? How would you know which wires paired with whichtqcm6b,/myr p 80i +ir?

The use of higher-volatjd+sqqmc0+bm6 06 -vyg2mc7vh iz 6tage lines in homes — say, 600 V or 1200 V — would reduce energymyh6qg6mjm2vsbct zqc0+ +07vi- a d6 waste. Why are they not used?

A transformer designed for a a)1r8 zel xbs:120-V ac input will often “burn out” if connected to a 120-V dc source. Explain. [Hi bsl8) xa1rez:nt: The resistance of the primary coil is usually very low.]

How would you arrange tw8 dix/o4 8aatno flat circular coils so that their mutual inductance was d xtaa48o/ni8
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery ing(;nl,ht4q0xw+ pq(gbjo+o5ucrd6. am z 7f r (Fig. Below) affect the time needed for the LR circuit to reach 6a4g5o r7( t(un0 zgqd,qcr ;mw xf pho.b++jl
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltagpi0c/xz8v m cek0z)-w e across
(a) an inductor, ----待选择----yesno 
(b) a capacitor, be greater than the rms voltage of the ac source? Explain. ----待选择----yesno 

Describe briefly how the frequency of the source emf a -g8 ob.mks/fbffects the impedance of
(a) a pure resistance,
(b) a pure capacitance,
(c) a pure inductance,
(d) an LRC circuit near resonance (R small),
(e) an LRC circuit far from resonance (R small).

Describe how to make the impedance in9yw(c wk8 d7zejrr) )*va9ami an LRC circuit a minimum.

  The magnetic flux through a coil of wire cisbt 6sc -hgv37q;xdls/r;;u ontaining two loops changes from -50Wb to +38 Wb in 0.42 s. What is the emf induced in s;7xgt-;c vs3/r ibu lhqd; 6sthe coil?    V

  The rectangular loop shown in (Fig. Below) is pushed into the magnetic fio8p(o ax/hid7b yj-(p 1qxlr(eld which points inward. In what directiol(rj/ 7pq(dib (h -o1pa xx8yon is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being inserted into the o j6eycp3 s/-scoil. In which direction is the induced cup-y6 ssj /3coerrent flowing through the resistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wire is in a 1.10-T ma5pzv21e q* *f gw1xsh(m1m, nqdv0 vccgnetic field. The loop is removed from tcdc5 * * 1zf20(g1s,vhq we1vmpxnm vqhe field in 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially oriented perpendicular t 4c 8+hsm/xdl;oyin(zo a 1.5-T magnetic field. The loop is rotated so that its plane is parallel to the field directionz;cd8mxsiyn( 4 /ol+h in 0.20 s. What is the average induced emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially n8mb ry0hq e*xd(2t75 drst. poriented so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.15 s, the field is changed to one of 0.25 T pointih7 stt8y 02rdr5 (bqpx .e*dmnng down. What is the average induced emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of wire is pl1v 0i)zi. ijfwq3bb0,jx ypy /aced in a 0.50-T magnetic field.
(a) When the plane of the loop is perpendicular to the field lines, what is the magnetic flux through the loop?    $ \times10^{-3 }\;Wb$
(b) The plane of the loop is rotated until it makes a 35$^{\circ}\,$ angle with the field lines. What is the angle $\theta$ in Eq. 21–1 for this situation? $\theta$ =    $^{\circ}\,$
(c) What is the magnetic flux through the loop at this angle?    $ \times10^{-3 }\;Wb$

  (a) If the resistance of the resistor in (Fig. Below) is slowly inq 27bfn7dhwl5( :ry eht:g; socreased, what is the direction of the current induced in the small circular loop inside the larger loop?w:qs( l; 5 rbt: gehd7ynoh7f2  ----待选择----counterclockwiseclockwise 
(b) What would it be if the small loop were placed outside the larger one, to the left?  ----待选择----counterclockwiseclockwise 

  What is the direction of the induced current in the circular loop due to u4i6zva ej28pi,bzu j6cj84x the current shown in each part of (,c6j8e8zau2buji4 p z 6jiv4xFig. Below)?
a  ----待选择----counterclockwiseclockwise0 
b  ----待选择----counterclockwiseclockwise0 
c  ----待选择----counterclockwiseclockwise0 
d  ----待选择----counterclockwiseclockwise0 

  If the solenoid in (Fig. Below) is being pulled away from the loop shown, in whazay s+vaw:c;vc- 8g5.3qt1nh8kd ccpt direction is the induced current in the 3;s w+8ga1ak5 ycccd-v.tc :nzhv8qploop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wij9h13u92) ixfy no32y ucjt8b j mj9xyre loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the fi92i39n3x ojj2hb 91fyt uyy jxuj)m 8celd points away from an observer the observer.
(a) Calculate the induced emf.    $ \times10^{-2 }\;V$
(b) In what direction does the induced current flow?  ----待选择----counterclockwiseclockwise 

  The moving rod in (Fig. Below) is 12.0 cm long and is pulled at a spee+f7* me4gxfjzx/-f qyqe2mu3d of 15.0cm/s If the magnetic field is 0.800 Tgm7e xfq/ue4z*y -3fxf2 qm+j , calculate
(a) the emf developed,    $ \times10^{-2 }\;V$
(b) the electric field felt by electrons in the rod.    V/m  ----待选择----updown 

  A circular loop in the plane of the pafz uk wjskfn)4f)q0//m:v7pr b jcx6 2per lies in a 0.75-T magnetic field pointing into the paper. If the loop’s diameter changes from 20.0 cm to 6.0 cm in 0.50 b)f 7z2n: x0vjcr f6fu/km k/qwjp)4 ss,
(a) what is the direction of the induced current,  ----待选择----counterclockwiseclockwise 
(b) what is the magnitude of the average induced emf, $|\varepsilon|$ $\approx$    $ \times10^{-2 }\;V$ (retain one decimal places)
(c) if the coil resistance is 2.5$\Omega$ what is the average induced current?    $ \times10^{-2 }\;A$

  The moving rod in (Fig. Below)is 13.2 cm long and generates an emf39d, mkjy g/4uz (godd/;gzw8uxom0 j of 120 mV while moving in a 0.90-T magnetic fikz ;y3gmx / /9jd8dozgmg0uouj, (w4d eld.
(a) What is its speed?    m/s
(b) What is the electric field in the rod?    V/m  ----待选择----updown 

  Part of a single rectangular loop of wirusm8y9+e7+ beg iz+p alqr8,x e with dimensions shown in (Fig. Below) is situated insideayeez, 7m+8srxp+i 8 uq+g bl9 a region of uniform magnetic field of 0.550 T. The total resistance of the loop is $\mathrm{0.230~Ω}$ Calculate the force required to pull the loop from the field (to the right) at a constant velocity of 3.40m/s Neglect gravity.    N

  A 500-turn solenoid, 25 cm long, has a diameterbcq: l g,*bqu(ax6p f( of 2.5 cm. A 10-turn coil is wound tightly uap *:lb6gc ,x q(bqf(around the center of the solenoid. If the current in the solenoid increases uniformly from 0 to 5.0 A in 0.60 s, what will be the induced emf in the short coil during this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves3p120tyvq qajq:bl6k7ud f, f with a speed of 1.6m/s is 30.0 cm long, and has a resista 1qbuafq,py6jd f:k 7t23vl0q nce of $\mathrm{2.5~Ω}$ The magnetic field is 0.35 T, and the resistance of the U-shaped conductor is $\mathrm{25.0~Ω}$ at a given instant. Calculate
(a) the induced emf, $\varepsilon$ $\approx$    V(retain two decimal places)
(b) the current in the U-shaped conductor, $I\approx$    $ \times10^{-3 }\;A$ (retain one decimal places)
(c) the external force needed to keep the rod’s velocity constant at that instant. $F\approx$    $ \times10^{- 4}\;N$ (retain one decimal places)

  A 22.0-cm-diameter coil consists5kr8 c(xt qnc --dgmc+v(m3sd of 20 turns of circular copper wire 2.6 mm in diameter. A unin3c(-c 5qmkxmsdt8-r(+ v gdc form magnetic field, perpendicular to the plane of the coil, changes at a rate of $8.65\times10^{-3}\mathrm{~T/s}.$ Determine
(a) the current in the loop, $|\varepsilon|$ $\approx$    A (retain two decimal places)
(b) the rate at which thermal energy is produced.    $ \times10^{-4 }\;W$

  The magnetic field perpendicuf*jrft* 6 /agolar to a single 13.2-cm-diameter circular loop of copper wire decreases uniformly from 0.750 T to zero. If the wire is 2.25 mm in diameter, how much charge moves past a point in the coil d f/rtoga* *f6juring this operation?    C

  A simple generator is used to generate a 08sv qt, o 0ffb;qbb;mpeak output voltage of 24.0 V. The square armature consists of windings that are 6.0 cm on a side and rotates in a field of 0.420 T at a rate of 60.0rev/s How many loops of wire sq,b0ft m oq;;fb08vsb hould be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idlingkdi jiuq)+1nbk s+01i at 1100 rpm produces 12.4 V. What will the ou tput be at a rotation speed of 2500 rpmu )j+b1d isi+kk1qn 0i, assuming nothing else changes?    V

Show that the rms output:q8)uvhwrz a2s6s 29 n +lxqvq .-tnqx (Section 18–7) of an ac generator is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop square coil 21.0 cm on a side. How fas3*(uzzv n8qzx7gu 30 uo vo*xzt must it turn in a 0.65vv308 ouzzxu*3(* qug7 nxozz0-T field to produce a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil with a diamq d0 -7cd6yzaceter of 8.0 cm rotates at 120rev/s in a uniform magneticaq d7 0z-cdcy6 field of strength 0.55 T.
(a) What is the rms voltage output of the generator? $\approx$    V (Round to the nearest integer)
(b) What would you do to the rotation frequency in order to double the rms voltage output?  ----待选择----oncedoubletriple  the rotation frequency

  A generator rotates at 85 Hz in a magnetic fieldpgb92ifx lh 41 of 0.030 T. It has 1000 turns and produces an rms voltagb2 1lhf9i4xpg e of 150 V and an rms current of 70.0 A.
(a) What is the peak current produced?    V
(b) What is the area of each turn of the coil?    $ \times10^{-2 }\;m^2$

  A motor has an armature r+k1.:6jmzje n+j pv+ dto.)tg(g8m bl smvz 1uesistance of $3.25\Omega.$ If it draws 8.20 A when running at full speed and connected to a 120-V line, how large is the back emf?    V

  The back emf in a motor is 72 V when operating at 1800 rpm. What would be ,pr 3wr vrfc8 :bw,*wi3d3: rfaht,hcthe back emf at 2500 rpm if the magnetic field is uncha*fwdc3ch: 3vwfh,rr :bitr,a,8w3 prnged?    V

  The back emf in a motor is 95 V when the motor is oy il4/ kxk5;n :;9 coqr6agjvnperating at 1000 rpm. How would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the motor was ;ox4/vyq n:jn k6a59 irgl;ckrunning at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the current in the6e9nta )lxl r; motor of Example 21–9 if the load causes it to run at half speltn6er ;xl9 )aed?    A

  A transformer is designed t40rp g-h9weafw:9j xio change 120 V into 10,000 V, and there are 164 turns in the primary p9iewh40r- xwag:j 9 fcoil. How many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 V. What is the ji,:zu9r: u(g 0hygdb 4 htx5lcurrent in the secondary coi,(t4y zu jbx:g0lduh h:9g5 ril as compared to the primary coil?   

  Neon signs require 12 kV for their operaxr;brnso,;cqdh hb yb-/)5.im. ii(7w ebp+ ition. To operate from a 240-V line, what must be the ratio of secondaryqx+ypb. )r ii;, i sbwhb(c-r.o ;5bn/ehd7mi to primary turns of the transformer? What would the voltage output be if the transformer were connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer plugs into 120-V ac and draws 0.35 A while supv.d5k fbt/3jpln/o3gplying 7.5 A to the tr. /3lvn53tj/go pbf dkain.
(a) What voltage is present across the tracks?    V
(b) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer

  The output voltage of a 95-W transformer is 12 V, and the input curren e*1p(da. essvt is 22 A. pee v1as(*sd .
(a) Is this a step-up or a step-down transformer? this is a  ----待选择----step-downstep-up  transformer
(b) By what factor is the voltage multiplied? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =   

  A transformer has 330 primary turns and 1340 secondary turns. The inp qd6 wv38a3s05dvj0 f;sowizzp/g)ku ut voltage is 120 V and the output current is 15.0 A. What ardw)3guv;k 0 i 6fa5v zjpd0/ swqs83oze the output voltage and input current? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =    V
$\frac{I_\mathrm{s}}{I_\mathrm{p}}$ =    A

  If 30 MW of power at 45 kV (rms) arr*dll 359kj)cf fs4l, jas n,lvives at a town from a generator via $\mathrm{4.0-Ω}$ transmission lines, calculate
(a) the emf at the generator end of the lines, $\varepsilon$    V
(b) the fraction of the power generated that is wasted in the lines. fraction wasted   

  65 kW is to arrive at a jh:z p+ 5js;scze+ca6 35blfp town over two $0.100-\Omega$ lines. Estimate how much power is saved if the voltage is stepped up from 120 V to 1200 V and then down again, rather than simply transmitting at 120 V. Assume the transformers are each 99% efficient.    kW

  If the current in a 180-mH coil changes steadily from 25.0 A to 10.0 A in 350 msto+:ku nr7(h(r y jvb+, what isounryrh7+jv(:( k+tb the magnitude of the induced emf?    V

  What is the inductance of a coil if the coil produces an emf of 2. pz aej n,ejh.+xw:0q:50 V when the cn:xhjzpj q:0+w, .eaeurrent in it changes from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-fille g8w,lfy lh,2ed coil 2.9 cm in diameter containing 10,000 loops2wl8h ,yf g,el?    H

  How many turns of wire would be required to make a c6.e:u;nvhx 9 u kqwe.130-mH inductance out of a 30.0-cm-lo; 6eh.ucx9v :ekn uw.qng air-filled coil with a diameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, em x.7hi. ytvl 0c2tofp6 uq+* *rcan3+v;beb and it is 2.5 cm in diameter ant+h; v73 ceml+yb.pt*or q2c6 x i*b0eva.ufnd 28.2 cm long.
(a) What is its inductance?    $ \times10^{-2 }\;H$
(b) How many turns would you need to generate the same inductance if the core were iron-filled instead? Assume the magnetic permeability of iron is about 1200 times that of free space.

  A coil has $2.25-\Omega$ resistance and 440-mH inductance. If the current is 3.00 A and is increasing at a rate of 3.50A/s what is the potential difference across the coil at this moment?    V

A long thin solenoid of length l and crkjk-o0. o hy7soss-sectional area A contains $N_1$ closely packed turns of wire. Wrapped tightly around it is an insulated coil of $N_2$ turns, (Fig. Below). Assume all the flux from coil 1 (the solenoid) passes through coil 2, and calculate the mutual inductance.

  The wire of a tightly wound solenoid is unwound and used to make anoth,(t 9bss:-ei6s-lbf g3o o ogzer tightly wound solenoid of twicbo-,ibzlss6:(3fgget - o 9 soe the diameter. By what factor does the inductance change?   

  The magnetic field inside an air-filled solenoid 3x) 25uuj o5qsi6 cm long and 2.0 cm in diametj )5 xouq5si2uer is 0.80 T. Approximately how much energy is stored in this field?    J

  At a given instant the current through an inductor is 50iou(kb*85gbfocu (. bg6ze d2.0 mA and is increasing at the rate of 115mA/s. What is the initial energy stored in the inductor if the inductance is known to be 60.0 mH, and how long does it take for the energy to increasbk*(g58 ecubo 2i o(bd.6fzuge by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s magrlks3a3fr/a ot .37r/ lifw8jnetic field averages about $0.50\times10^{-4}\mathrm{~T}$ near the surface of the Earth, estimate the total energy stored in this field in the first 10 km above the Earth’s surface.    $ \times10^{15 }\;J$

Determine $\Delta I/\Delta t$ at t = 0 (when the battery is connected) for the LR circuit of (Fig. Below) and show that if I continued to increase at this rate, it would reach its maximum value in one time constant.

  After how many time constants does the currentcsit/g 9 - x:qnquc40r -se(mn in (Fig. Below) reach within
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoids have the same length r f+7)7c0y5etzy u4 s4 jddnteand circular cross-sectional area. But solenoid 1 uses wire that is+544 sne yj 0z)uddtfrtc77ey half as thick as solenoid 2.
(a) What is the ratio of their inductances? $\frac{L_1}{L_2}$ =   
(b) What is the ratio of their inductive time constants (assuming no other resistance in the circuits)? $\frac{\tau_1}{\tau_2}$ =   

  What is the reactanc) ua9 jris ,blzjj0);te of a $7.20-\mu F$ capacitor at a frequency of
(a) 60.0 Hz,    $\Omega$
(b) 1.00 MHz?    $ \times10^{ -2}\;\Omega$

  At what frequency will a 22.0-mH inductor have a reanafb2w 48 ux*ou 5sy+*;uurp vctance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will7w qa5o t42ho-nxf/a q a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the r ba(1;jg-0qevr2q flleactance of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a g1fw.nzd y57u8ajqvvcc9p02 2 yyy8e 1.0-mH inductor as a function of frequency fro 07a8z5cgpcu jy 12 yv.82qnvdy9wf eym 100 to 10,000 Hz.

  Calculate the reactance of, and rms current in, a 160-mH radio c:cxc lsqw q6skp(b9 (8oil connected to a 240-V (rms) 10.0-kHz ac line. Ignore resistancecxbwqs l8( (k:9s6c qp.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It d r0fb 6+rocmo2k/5fmkraws 12.8 A. What is the coil’s r mf6/0fkmobok 5c+2rinductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a well-i-f8)3 zgepkp jnsulated $0.030-\mu F$ capacitor connected to a 2.0-kV (rms) 720-Hz line?    $\Omega$
(b) What will be the peak value of the current?    A

  $\mathrm{A~30-k}\Omega$resistor is in series with a 45-mH inductor and an ac source. Calculate the impedance of the circuit if the source frequency is
(a) 50 Hz,    $ \times10^{4 }\;\Omega$
(b) $3.0\times10^4\mathrm{~Hz}.$    $ \times10^{4 }\;\Omega$

  $\mathrm{A~3.5-k}\Omega$ resistor and a $4.0-\mu F$ capacitor are connected in series to an ac source. Calculate the impedance of the circuit if the source frequency is
(a) 60 Hz,    $ \times10^{3 }\;\Omega$
(b) 60,000 Hz.    $ \times10^{3 }\;\Omega$

  For a 120-V rms 60-Hz voltage, an rms current of 70 mA passing through thecg/ *j,*;va/)xx bftfr8rjfi human body for 1.0 s could be leja8x/rfx/ i r*, ;jbtvf*cgf )thal. What must be the impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil ifzf.dt3;(br 0yb h;yrf its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms current in an LRC circuit coz51 c wsij .p z ttqi3rm23vno0 3(oucg90*nzrnnected to a 13o*ncn z 32 zwz.9pmt35rt0g1isr(iu voq0 jc0.0-kHz, 725-V (rms) source if $L=22.0\mathrm{~mH},R=8.70\mathrm{~k}\Omega,$ and
Z $\approx$    k$\Omega$
$\phi$ =    $^{\circ}\,$
$I_{rms}$ =    $ \times10^{ -2}\;A$

  A resistor in series with a 420-mH inductor is driven by an ac power suyjm3mwr,(rx:2n c :supply. At what frequencyx 2rjucm (sm::,y r3wn is the impedance double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in an RL circuit when a 60.0-Hz 120-V rms ac voltaetrpcxpv *r,/:hb5 + gebyo)tlp 8qx6432qpp ge is applied, why3ol2 c4 x vpbp:qrrp6b pp,eg/x htt+)qe58* ere $R=1.80\mathrm{~k}\Omega,$ and $L=350\mathrm{~mH}?$    $ \times10^{ -2}\;A$
(b) What is the phase angle between voltage and current?    $^{\circ}\,$
(c) What are the rms voltage readings across R and L?
$V_{rms \,R}$ $\approx$    V (Round to the nearest integer)
$V_{rms\,L}$ =    V

  (a) What is the rms current in an x0a8e xyuag)00goa x5wwj9+ whqa u-4 RC circuit if $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ and the rms applied voltage is 120 V at 60.0 Hz?    $ \times10^{-2}\;A$
(b) What is the phase angle between voltage and current? $\phi$ =    $^{\circ}\,$
(c) What are the voltmeter readings across R and C?
$V_{rms\,R}$   V
$V_{rms\,C}$    V

  A 3500-pF capacitor is conneoh0v)m-cxm +ju;wjz64k wx9 5y:ftfbcted to a $55.0-\mu H$ coil of resistance $3.00\Omega.$ What is the resonant frequency of this circuit?    $ \times10^{5 }\;Hz$

  The variable capacitor in the tuner of an AM radio has a capacitance of 280nohp:chq i;2u 90fui /0 pF when the radio is tuniohu29hq fcuip0:n ; /ed to a station at 580 kHz.
(a) What must be the capacitance for a station at 1600 kHz? $C_{1600\mathrm{~kHz}}$ $\approx$    pF(Round to the nearest integer)
(b) What is the inductance (assumed constant)?    $ \times10^{ -5}\;H$

  An LRC circuit has L = 14 -5usqt8po7g6g5e tao.8 mH and $R=4.40\Omega$.
(a) What value must C have to produce resonance at 3600 Hz?    $ \times10^{ -7}\;F$
(b) What will be the maximum current at resonance if the peak external voltage is 150 V?    A

  Suppose you are looking at two cu4yn i*jng2z(v rrent loops in the plane of the page as shown in (Fig. Below). When switch 4g jnyv*izn(2 S is thrown in the left-hand coil,
(a) what is the direction of the induced current in the other loop?  ----待选择----counterclockwiseclockwise 
(b) What is the situation after a “long” time?
(c) What is the direction of the induced current in the right-hand loop if that loop is quickly pulled horizontally to the right?  ----待选择----counterclockwiseclockwise 

  A square loop 24.0 cm on a side has a resist*h7zqx;ll el,ance of $5.20\Omega.$It is initially in a 0.665-T magnetic field, with its plane perpendicular to $\vec{\mathbf{B}},$ but is removed from the field in 40.0 ms. Calculate the electric energy dissipated in this process.    $ \times10^{-3 }\;J$

  A high-intensity desk lamp is rated at 45 W but e80; u-np )04p0mtl )3f qtxfo;ykcio0m zdinrequires only 12 V. It contains a transformer that converts 120l4 fmn)-noizuti0 ;0kxeyt0d c p;mof3)08pq-V household voltage.
(a) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer
(b) What is the current in the secondary coil when the lamp is on?    A
(c) What is the current in the primary coil?    A
(d) What is the resistance of the bulb when on?    $\Omega$

  Power is generated at 24 kV at a generating plant located 118 km from a town 3bv+:boi pgv ,*vybl+that requires 50 MW of power at 12 kV. Two transmission lines from the plant to th,+ygv vl*pob+bb :3vie town each have a resistance of $0.10\mathrm{~}\Omega/\mathrm{km~}.$ What should the output voltage of the transformer at the generating plant be for an overall transmission efficiency of 98.5%, assuming a perfect transformer? V $\approx$    kV

  The primary windings of a transformer which ha zo8alda.hls + f;)qd g8zsn95 2wva:cs an 80% efficiency are connected to 110-V ac. The secondary windings arqf:zo l;sah+ dg58aaw8)v d2n ls.z9ce connected across a $2.4-\Omega$ 75-W lightbulb.
(a) Calculate the current through the primary windings of the transformer. $P_S$ $\approx$   A
(b) Calculate the ratio of the number of primary windings of the transformer to the number of secondary windings of the transformer. $\frac{N_\mathrm{p}}{N_\mathrm{s}}$   

  A pair of power trannv8k 26 afrm-u wj0s6zsmission lines each have a $0.80-\Omega$ resistance and carry 740 A over 9.0 km. If the rms input voltage is 42 kV, calculate
(a) the voltage at the other end, $\approx$    kV
(b) the power input, $\approx$    $ \times10^{7 }\;W$
(c) power loss in the lines, $\approx$   $ \times10^{5 }\;$W
(d) the power output. $P_{out}$ $\approx$    $ \times10^{7 }\;W$

  Two resistanceless rails rest 32 cm apartxp cj002 y/ ,z km3ktq1wv7( ktva8ihw on a 6.0$^{\circ}\,$ ramp. They are joined at the bottom by a $0.60-\Omega$ resistor, and at the top by a copper bar of mass 0.040 kg (ignore its resistance) is laid across the rails. The whole apparatus is immersed in a vertical 0.55-T field. What is the terminal (steady) velocity of the bar as it slides frictionlessly down the rails? v =    m/s

Show that the power l/0 5g+askuqm1 vs vhy-f1*mjfoss in transmission lines, $R_L$ is given by $P_{\mathrm{L}}=\left(P_{\mathrm{T}}\right)^{2}R_{\mathrm{L}}/V^{2},$ where $P_T$ is the power transmitted to the user, V is the delivered voltage, and $R_L$ is the resistance of the power lines.

  A coil with 150 turns 7lqewz *:+vm36l+mw lkts /gw, a radius of 5.0 cm, and a resistance of $\mathrm{12~Ω}$ surrounds a solenoid with $230\mathrm{~turns/cm}$ and a radius of 4.5 cm; see (Fig. Below). The current in the solenoid changes at a constant rate from 0 to 2.0 A in 0.10 s. Calculate the magnitude and direction of the induced current in the coil.
I =    $ \times10^{-2 }\;A$
 ----待选择----left to rightright to left 

  A certain electronic device needs to be protected againsk0q 8**/nvbcush p -zot sudden surges in current. In particular, after the power is turned on the current should rise no more than 7.5 mA insph*b0c8* zqv/k o un- the first $120\mu s$ The device has resistance $\mathrm{150~Ω}$ and is designed to operate at 55 mA. How would you protect this device? L $\approx$    in series(retain two decimal places)

  A 25-turn 12.5-cm-diameter coil is placed bed7*l 0 vac,gbm25fd aytween the pole pieces of an electromagnet. When the magnet is turned on, thaygv*lm2d0c5,afb d7 e flux through the coil changes, inducing an emf. At what rate (in T/s) must the field produced by the magnet change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simplednt 4qr; qjnp6 gzx183 generator whose square armature windings are 6.68pg j6x zq;13nd4trqn 0 cm on a side; the armature contains 155 loops and rotates in a field of 0.200 T at a rate of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for electric and magnetic fields attained in laboratories a9go(a 6 ywyvf6re about f6ya9(ov6gwy $1.0\times10^4\mathrm{~V/m}$ and 2.0 T.
(a) Determine the energy density for each field and compare.
$u_E$ $\approx$    $ \times10^{-4 }\;J/m^3$
$u_B$ $\approx$    $ \times10^{6 }\;J/m^3$
$\frac{u_B}{u_E}$ =   $ \times10^{9 }\;$
(b) What magnitude electric field would be needed to produce the same energy density as the 2.0-T magnetic field?    $ \times10^{8 }\;V/m$

  What is the inductance L of the primary of a transformer whose input iskr 7)gjwf97c4dzee-k pfmy . ( 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no currentkf9epf7 )g4y e(zj k.d7rm-cw in the secondary.    H

  A 130-mH coil whose resisef o0t)c0 4di3yrzr3f9 mjsgg /r1 h8atance is $\mathrm{18.5~Ω}$ is connected to a capacitor C and a 1360-Hz source voltage. If the current and voltage are to be in phase, what value must C have?    $ \times10^{-7 }\;F$

  An inductance coil draws y rbke//f6f8t2.5-A dc when connected to a 36-V battery. When connected to a 60-Hz 120-V (rms) source, the current drawn is 3.8 A (rms). Determine the indub8tf/f6 kery/ ctance and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor withm6ncf3 cz.lo m*x 84lg $2.0-\Omega$ resistance is connected in series to a $20-\mu\mathrm{F}$ capacitor and a 60-Hz, 45-V source. Calculate
(a) the rms current, $I_{rms}$ =    A
(b) the phase angle. $\phi$ =    $^{\circ}\,$

  The Q factor of a resonance circuit can be defined as the ratejo;jk.kp8 j fv0l; q8io of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q factor, the sharper the re;kf;qp0okvjlj 8j 8.esonance curve will be and the sharper the tuning.
(a) Show that the Q factor is given by the equation $Q=(1/R)\sqrt{L/C}.$
(b) At a resonant frequency $f_0=1.0\mathrm{~MHz},$ what must be the values of L and R to produce a Q factor of 550? Assume that $C=0.010\mu\mathrm{F}.$ L $\approx$    $ \times10^{-6 }\;H$(retain one decimal places) Q =    $ \times10^{-2 }\;\Omega$