What would be the advantage, in Faraday’s experiments (Fig. Below), of usi8p4 nzqjsm;of w1i5g1 ng coils with many turns?1jqn1zp8mw5io 4gs f;

What is the difference betweeh b :j0dkvh2n9ko-wr)t d4i 8 gb*,zrcn magnetic flux and magnetic field?

Suppose you are holding a circular ring of wire and suddenly thrust a magnet, skise/p.-5 uvy lux;/kouth 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 induce.pisuk ev /;l-5yx u/kd when you withdraw the magnet? In each case, if your answer is yes, specify the direction.

Two loops of wire ar,ejz p*y q-w.*t9utvre moving in the vicinity of a very long straight wire carrying a steady current as shown in (Fig. Below). Find the direction of the inducedqv yw-9p**,tzjte.r u current in each loop.

Suppose you are looking along a line through the centers of two cs;t2eim0j8k r) p,bvpd q )mg3ircular (but separate) wire loops, one behind the other. A battery is suddenly connected to the front loop, establishing a clockwise cu qv ,g80)smprbj)imk2e3d;tprrent.
(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 direction of the induced f44o0nff+ brq;kb 3rns r8ar5 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 dista6ik7v(u gbm4c.xxs s n 3w 7h-aq)ie2bnce, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carryi.3 aq6xhn-mbsu (ksw2i4)ie v xb77c gng the return current. Why is a “shield” necessary?

What is the advantage t, loo /)*xvuzmmysjug,vqc.u*1 2 o1 of placing the two insulated electric wires carrying ac close together or e y*,.1)ujxsc vvo/2o ut mlqogmuz, *1ven twisted about each other?

Explain why, exactly, the lights may dim briefly when aevm ;i)8l*nyufu (x s. refrigerator motor starts up. When an electric heater il;)f *x i8sy.m v(uneus turned on, the lights may stay dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Bel (zzka;*ub q.low b) plus the right-hand rules to show why the counter torque in a generator opposes th; .l *bqazuz(ke motion.
a
b

Will an eddy current brake (Fig. Below) wok ,u ix(s+cmi6kk8k w(rk on a copper or aluminum wheel, or must the wheel be ferromagneti,kus( (kkw 8xkcm6 i+ic? Explain.

It has been proposed that eddy currents be used to help sort solid waste f icru 4mxo*ug j 8;6e (dppj6,fpy*-peor recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to slid*rpjd4(pycje g6u mpxeu;6 8- op,*f ie down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots i y8iosz)xqc2; n (Fig. Below) falls much more quickly through isx2o;)c q8z ya magnetic field than does a solid bar. Explain.

If an aluminum sheet kj2dbf.ayv, x h 6vbo *7hq:2his held between the poles of a large bar magnet, it requires some force to pull it out of the mab h j:yvvb2.x62 *,hq7af hkdognetic field even though the sheet is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a vertical metal tube reaches a terminal veloci4n5 yjn76 sblo5h,m(8ogbh eo ty even if the tube is evacuated so that there is no air resistance. E ,yogn(b8nso6h4 5eho 75j lbmxplain.

A metal bar, pivoted at one end, /n u2n6 eq:omte- kav*+y2rcfoscillates freely in the absence of a magnetic field; but in a magnetic field, its oscillations ar + mqc2*nkny6ef2vau /-tr:e oe quickly damped out. Explain. (This magnetic damping is used in a number of practical devices.)

An enclosed transformer has four wire leads c g1 nw,f)jao*7j bu*fooming 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 which?fbjgj* a7 wf) *n1uo,o

The use of higher-voltage lines in homes j d0ag:jekh tidq( t5lk1;(j1 — say, 600 V or 1200 V — would reduce energy waste. Why are th jjt 5k1( tk:(0liddhg j;aq1eey not used?

A transformer designed for a 120-V ac input will often “burn on y gp6d(;bzj0ut” if connected to a 120-V dc source. Explain. [Hint: The resisn bg0j;yp (z6dtance of the primary coil is usually very low.]

How would you arrange two flat circular coils so that their mutual induct/-, q4wgdc hiaance waw i-c,q adh4/gs
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery intu8uxjmc 5rh-6e w -0,ier b/v (Fig. Below) affect the time needed for the LR circuit to reach -hbeu86-, t xrmi0jue 5rv/w c
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltage acrosssl-rxyiy95 +,ouwbn3d 8d, zt
(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 o+kweckwr -2 t)f the source emf affects 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 f, a6+ t7tb8b hxflbf7the impedance in an LRC circuit a minimum.

  The magnetic flux through a coil of wire containing two loops changes ff/nvqm c ,6/z6g x6ohprom -50Wb /xg/co, m 6h6nqvp zf6to +38 Wb in 0.42 s. What is the emf induced in the coil?    V

  The rectangular loop shown in (Fig. Below) if+1w 01 efoepqs pushed into the magnetic field which points inward. In what direction is the induced current ffe11e+ pqwo0?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below*7 s. bxbfoc m3e2(cvp) is being inserted into the coil. In which direction is the induced current flowing through the resist(p *c3m s.ceb voxf2b7or R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wire is in a hswlq2 n3sd88u3)n se 1.10-T magnetic field. The loop is removed f38)hl se suw3dns2 q8nrom the field in 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is init s)pmox;v /h3hially oriented perpendicular to a 1.5-T magnetic field. The loop is rotated so that its plane is parallel to the fieldmoh s)/xhv 3p; direction 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 oriented so that itsgw*3tb -x)cp b 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 pointing down. What tc3 wxp)g-bb *is the average induced emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of wire is placed in a 0e yzo93zbz6.v62 n obn.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 resistanceu 8l,+*vlv0aoomnx/wi m;r o) of the resistor in (Fig. Below) is slowly increased, what is the direction of the current induced in the small ow*m nilvrm/ );0u+o8 vlox,acircular loop inside the larger loop?  ----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 rv50) (ebt -nojaw.pq due to the current shown-5taobnpwej v.q(r 0) in each part of (Fig. 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 puy5-c4iybh8t: b w2qh olled away from the loop shown, in what direction is the induce 2 -h4bobyc:58 tyqhiwd current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire loop 12.0 cm in p1;xs*xum jo-5us 4bn lfc+,udiameter is changed from +0.52T to -0.45 T in 180 ms, where m ;ou+xbms5uujc*s l14xpnf -,eans the field 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 apam5zgrw k7y6;j3t /qs4cdw 7nd is pulled at a speed of 15.0cm/s If the magnetic fiedr;wg57y/m kca7qwj s pzt 436ld is 0.800 T, 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 paper lies in a 0.75-T magnetic fieltmwo r0frv9sm-+5tp. * fe ,nbd pointing into the paper. If the loop’s diameter chanmtr0 w f-+,.5mn frb pot*ev9sges from 20.0 cm to 6.0 cm in 0.50 s,
(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. Be; q5u+qsau +v eff*g6olow)is 13.2 cm long and generates an emf of 120 mV while moving in a 0.90-T magnetic *6q+veauog u+f;5s fqfield.
(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 wire with dime hyg c.e3jld .ghwo6l/zb0 b9p d4d 70n(bwfe2nsions shown in (Fig. Below) is situated inside a region of uniform magnetic field o 4l6gy(o.2de/9 fd 73gplj0b0dhebb zhcn.ww f 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, y/ chg:gcze.w4or7 ihbjr/9(has a diameter of 2.5 cm. A 10-turn coil is wound tightly around the center of the solenoid. If the current ey b.g iw/zrj:hc94h(rc o7 g/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 moves with a speeh.l3ps) l)rwk0i:ts g d of 1.6m/s is 30.0 cm long, and has a resistanc 3ikw:psh0llsr.) )tg e 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 consists of 20 turns of circular copper wire ttyoq,ck xdi 2*/sb37s 6 mp2u2.6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, changes at 6*tbp,x7ysmk 3d o2 qu sc/2tia 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 perpendicular to a single 13h1.q*mlt zzubogsw61cass * 1/i j/b2.2-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 p/2jzbh11 ims1qou lg*6c w.bt/ s*azsast a point in the coil during this operation?    C

  A simple generator is used to generate a peak hao(2r.tfx6 i4m svz3output voltage of 24.0 V. The square armature consists of windin4t2( mvi xofz.a srh36gs 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 should be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car i1w-rn gm-4o3b odnv tt/l 0 1qnn46odgdling at 1100 rpm produces 12.4 V. What will the ou tput be at a rotation -bnnl/d1 m1g4rtnv3ongd 0 64w-qoot speed of 2500 rpm, assuming nothing else changes?    V

Show that the rms output (Section 18–7) of 5rj::m(ekag d 4syh2x7/jz kgan 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 cmvc;bi1ona)xbe 8 ; uj7 on a side. How fast must it turn in a 0.650-T field to produce a 120-V peak outputo1 i ;;ja cxv7)enu8bb? $f$   rev/s

  A 450-loop circular armature coil with a if*l)t e--grpdiameter of 8.0 cm rotates at 120rev/s in a uniform mte-i-g lfp)*ragnetic 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 field of 0.f4owz dsu1 1g8nq y.24a2zdv z030 T. It has 1000 turns and produces an rms voltage of df41o8as.y 2412g zzwdnu zqv 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 resistllboi29x )ul, 9k0gcnance 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 wouldue 6qo;j7nfq( be the back emfj;e nu6(qfoq7 at 2500 rpm if the magnetic field is unchanged?    V

  The back emf in a motor is 95 V when the motor is operating at 1000 rpm. How u-vlaa0g 3/t h5(thygn:8 qnrua 3n7iwould you change the motor’s magnetic field/ n : 75yan au(0avgtrq3 3guh8lnith- if you wanted to reduce the back emf to 65 V when the motor was running at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the current in the motor of Eemo qf/qene t0-i u2oo;3/g d1xample 21–9 if the load causes it to run at half spg3;o q ote20m-/i qo/e1fdnue eed?    A

  A transformer is designed to change 120 V into 10,000 V, and thsc22;.fqu;8v ezzeu+h k)p as ere are 164 turns in the primary coil. Hoz+v fzu8;q;sp22 eehsa ku)c.w many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120qi9 5ghbd+ ,zmo)yb 9y V. What is the current in the secondary coil as comp bymzh 9i5b,) 9qdyo+gared to the primary coil?   

  Neon signs require 12 kV for their operation. To openf t t q9y450g,u gxtxpaw/6i1rate from a 240-V line, what must be thx1g6 n9g5f , tui tx/apwt0qy4e ratio of secondary 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 j* elf4wdt41fA while supplying 7.5 A to thefj*wtd 4 4e1fl train.
(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 cehf. cj p5v1+s*y-fidurrent is 22 A. pfc1ifejs.y+*d v-5 h
(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 ty1in. o: *nyvqeh-pxv w1k807u pt6hgurns and 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A. What are the outputv -.h1o*81p x q:6ui7yhv pynwng0ekt 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) arrives at a town from a generatzt 9tzysye )j/9q*e3dxnt- r0or 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 k)r r2lm+c) zca 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 ch4 -d1q dnj* fn.egoi6ydva2j (anges steadily from 25.0 A to 10.0 A in 350 msjg6*(dj dfq-1ny 2na vie4. do, what is the magnitude of the induced emf?    V

  What is the inductance 8;oy - );2x-og3hivhtpe. r zdms*vyhof a coil if the coil produces an emf of 2.50 V when the current in it changes from -28.0mA to +31.0mA in-.oh zyto2xv;*hpihvm-dsg38 ey; )r 12.0 ms?    H

  What is the inductance L of a 0.60-m-longs . 2cqju7wi0i air-filled coil 2.9 cm in diameter conta ciu7s2q 0wi.jining 10,000 loops?    H

  How many turns of wir.2ijibnv ;bph 0bvm *-e would be required to make a 130-mH inductance out of a 30.0-cm-long air-filled coil with a dij bvh- v.*0mb2;n iipbameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and it is 2.5 cm in diam2jw onl.dq2 4r0nt h1keter ql.k0jhnt2 w d41 2nroand 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 of8pl cl+13 exas5 a8vmxa kx*y7 length l and cross-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 dfvi6 f,a )azr 8+km f6rk8cl:iv(d8iw)z*tvwound solenoid is unwound and used to make another tightly wound so )vkmz 8w8rir df,6d6faf i(+lviaz:)vktc8*lenoid of twice the diameter. By what factor does the inductance change?   

  The magnetic field inside a)0;orw.qz y ozn air-filled solenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how muqz wo0y) ;.ozrch energy is stored in this field?    J

  At a given instant the current through an inductor i v/ebu v+nk56 1xmlc kz2fxa3(s 50.0 mA and is increasing at the rate of 115mA/s. What is the initial energy stored in the inductor if the inductance is x a1mkl2vu/(3+ve5kxbfn6z c known to be 60.0 mH, and how long does it take for the energy to increase by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s magnerpoc6 btmfx:lf n(8+683k ek qtic 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 dk8dj ,e wqy(uv-p8 +tq vpc,:current 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 tha,um(e.r:ucyp ( 0 ibrd dmr7,e same length and circular cross-sectional area. But solenoimuai d0upyebc,:((rm,7 drr .d 1 uses wire that is 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 reactance o j8ssaaw/ox 94f 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 reactance ogo( czh x q-x)mp/6o4kf $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will:zi,ai,erv) tuu0 :ip a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reacta*rrm7i bwo85y:4ci1 q s+vvvance 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 1.0-r-a o5bkb/0 k)iq al/qv ;kss9mH inductor as a function of frequency from 100 sbaq9o k vbs5/a iq/k-kr;0l) to 10,000 Hz.

  Calculate the reactance oad7)tlc4*)o o/x z(wva48cbql; n ul df, and rms current in, a 160-mH radio coil connected to a 240-V (rms) 10.0-kHz ac line. Ignore resistt xvoa cl *ocua(n4zlbq4 ;7dl)8)/wdance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It draws 12.8 A. Wy9t;q, g87l1wsftwe g hat is the coil’s inductance? 78qfe9; ,t1gtgyw swl $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance i-3fl (sd sjp:of a well-insulated $0.030-\mu F$ 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 voltage9 , nb1w*re7yemnkz 1vvqt/8p , an rms current of 70 mA passing through the human body for 1.0 s could be lethal. What must be the*q18mytvrknz9pw 7 1 /e, bvne impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance r /gs(;fons)xj j+3zoof a coil if its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, ph8fnmu67 q ;.amc0renloi*p) g*hwm; uase angle, and rms current in an LRC circuit connected to afmme* .qc;wg;a7i)8 n*h0 pnouu6lr m 10.0-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 seri87gs/jdbi(7hz t . (u2 hgynfges with a 420-mH inductor is driven by an ac power supply. At what frequency is the impedance double that of thgtzfhh 7u2 ( 8nygisj(7g. db/e impedance at 60 Hz?    Hz

  (a) What is the rms currentyoat9;b6h n*/8; shydyfbmh. in an RL circuit when a 60.0-Hz 120-V rms ac voltage is applied, wheryah;y;sm 8n9 yht*/ 6fbb o.hde $R=1.80\mathrm{~k}\Omega,$ 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 currentejc4 *da77gw4kxvu +x6a /erb in an 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 cdr3mp *zm (cdf. uy182wl pxo;onnected 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 twltnu1 gj3d (k7-8jq che tuner of an AM radio has a capacitance of 2800 pF when the radio gjj ntl8 13 ukd7w-q(cis tuned 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 ;) eje32g9e oha9jvsi = 14.8 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 current loops in the plane of tno n05,lueyt yu))n+xhe page as shown in (Fig. Below). When switch S is thrown in the + y)y5n,xtnoluu)e0nleft-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 reedlj 7d2 bd :muqc / :3wbyygr9yr,,v1sistance 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 requires onlyibs(h +f y. 6enl/q1*gsc nij3 12 V. It contains a transformer that conver*+j l3eii1fn qs6sh bg(cy/ n.ts 120-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 lx aykxa l983v +lilt((ocated 118 km from a town that requires 50 MW of power at 12 kV. 3 klay+8t il( vl(axx9Two transmission lines from the plant to the 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 tb3 o8d4qj q4garansformer which has an 80% efficiency are connected to 110-V o3jg8 qaqd4b4ac. The secondary windings are 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 transmission lines each have 3a/idoyo2;+l p*sgt9uxfe; i 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 apart omrnw, cfy)ml2)+32jxrzt 8e r3me2us n 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 loss in transmission l;hizb 9,ei iz/ines, $R_L$ 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, a radius of 5.0j *610dxyv xt;*htfdn 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 against sudden surges(nsp6us /cow( in current. In particular, after the power is turned on the current should rise no more t(/ p(scso n6uwhan 7.5 mA in 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 betfangpk c94cb 3* t y;a1ay.c6uween the pole pieces of an electromagnet. When the magnet is turned on, the flux through the coil changes, inducing an emf. At what rate (in T9af*3 k.ya;61ty4pa c gncub c/s) must the field produced by the magnet change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltag ivducd.7q6: ge of a simple generator whose square armature windings are 6.60 cm on a side; the armature contaid g:c d.i7qvu6ns 155 loops and rotates in a field of 0.200 T at a rate of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for eleciqj/4wmqi85 s fw6j8 mtric and magnetic fields attained in laboratories are ab8wjiqmm s58qw 46f/jiout $1.0\times10^4\mathrm{~V/m}$ 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 w yay)xy,7w12 jb2cmng hose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no cu7y,gymjx) nac212w byrrent in the secondary.    H

  A 130-mH coil whose resis4s) wtn svbq2gh:yx4-) *ipiz tance 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 2.5-A dc when connected to a 36-V battery. When conner-rgb n/xdc0) cted to a 60-Hz 120-V (rms) source, the current drawn is 3.8 A (rms). Determine the induc x-)r rbndgc0/tance and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor withp-./tqk 2g2wn)jc3g px/ knnx $2.0-\Omega$ 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 u3jo9 1ctt4up the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. T3uu jtpto 9c14he larger the Q factor, the sharper the resonance 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$