What would be the advantage, in Faraday’s experiments. a;zq :pqg5)t) l5dt(r/v7bkympott (Fig. Below), of using coils wmr l:p py.tdvq(;o)t7)bza t q/ tg5k5ith many turns?

What is the difference between magnetic flux and magnetic mlq+d873s.ercw l p(ofield?

Suppose you are holding a circular ring of wire and sud5+ vm ekj c+dwhi gpo9uk*-4e*denly thrust a magnet, south pole first, away from you toward the center of the circle. Is a current induced in *m cpeogd* vk59h++u-wji k4 ethe wire? Is a current induced when the magnet is held steady within the ring? Is a current induced when you 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 wirf+x(2d lt.m tsx25fbfe carryingxf+b(tsm.x 2ld ft5 f2 a steady current as shown in (Fig. Below). Find the direction of the induced current in each loop.

Suppose you are looking along a line fke5l sfr e(2 c38:hmric2* 7mo8roudthrough the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected to the front loop, *2merco 8572c is mflrf3dr8e (kouh: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 direction(od3q-- x cetu 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 traveuxrt45 og q30p c3*suel over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return ueou xc5pq 3tr34*gs0current. Why is a “shield” necessary?

What is the advantage of placing the two0d,,rc(t f :ekw z6xxi insulated electric wires carrying ac close togethedt: w(f,kcr6xixz0e ,r or even twisted about each other?

Explain why, exactly, the lights may dim briefly when a refrigerator motor stcng0:sa2j* ihkttsrrx : 1q,8arts up. When an electric heater is turned on, the lights may stay dimmed as long as the he, nra jx r:0 tc*2qgth8s:i1ksater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plu1seufpebr.h4 ,q chd7h y iu(33:8eqv s the right-hand rules to show why the countyv dq:ci7h3f4shbeh (81r,eu q pe3.uer torque in a generator opposes the motion.
a
b

Will an eddy current brake (Fig. Below) wort n4*yxlfvh9j* ho0i0k on a copper or aluminum wheel, or musi0xh9 t*jhl*y v on04ft the wheel be ferromagnetic? Explain.

It has been proposed that eddy currents bv60 h dntxm3hhgei5; 5e 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 m6m vdh50hhen t;3i5g xetals (Al, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quickly throuo2wwqt,+ p 6uqgh a magnetic field than does a solid barou6,pw2q+q tw. Explain.

If an aluminum sheet is held between the poles ofs)xh/6w ,g hj +bqbgo7 d57wdt a large bar magnet, it requires some force t, dwsbjw/ 7+hhg6g)d5 x7 tobqo pull it out of the magnetic 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 znd/nlq(-b v hiq0v3*reaches a terminal velocity even if the dnz vvln-bi q3*/q(0htube is evacuated so that there is no air resistance. Explain.

A metal bar, pivoted at one end, oscillates freely in the absence ofxn*bxsy;30jf*z t+ jkg.j * sxq;k6ad 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 devices.sz*3jxkdx .qgkja0;by* 6sf*nx jt;+)

An enclosed transformer has four wire 0ih,jrb53fy/y z u.1)iggc uzleads coming from it. How could you determine the raj 0)fiug, y 3r/igzbyuzhc5.1tio of turns on the two coils without taking the transformer apart? How would you know which wires paired with which?

The use of higher-voltage lines in homes —lsebj-/ le j1v0ou5- +4 owj :ch7bbcd say, 600 V or 1200 V — would reduce energy wasteb+v u4j j5bj1/becdc :oew-07sol-l h. Why are they not used?

A transformer designed for a 120-V ac input will u e26qzm:d:0z: 9o m6jzeoqzdoften “burn out” if connected to a 120-V dc source. Exp e:9z0::zud6z2oqe zqmdoj m6lain. [Hint: The resistance of the primary coil is usually very low.]

How would you arrange two flat circular coiy. 1zchhd5tj(ls so that their mutual inductance was .dhtjc( 1yhz 5
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Below) affect the time needed for tz.7gt kq2j 30admobs +he LR circuikgq27+mz o0sadb 3. tjt to reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, ca8otxi* )mpy7vn the rms voltage 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 affects the impedance of e7w,jgnj j1zky4 fo+*
(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 in an LRC86m-- 4wlqpw mt kv.nr circuit a minimum.

  The magnetic flux throfved y03t0p+0u hs+eh ugh a coil of wire containing two loops changes from -50Wb to +38 Wb in 0.42 s. What is the emf induced +vusdf003 yhhe +0tpein the coil?    V

  The rectangular loop shown in (Fig. Below) is pushe0x7q ttkirtoh/m(5(c ) vs km8d into the magnetic field which poinvk0rxt ht8c)( oskit(m m/5q7ts inward. In what direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magzbmsuag+z, + -net in (Fig. Below) is being inserted into the coil. In which direction is the induced,ga s bu-z+zm+ current 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 1of(6 -b2rdsxkq:b.l z88eg lh .10-T magnetic field. The loop is removed from the field in 0.15 s. What is the averzsh godkl 8l.8( bxf-6b2erq:age induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially ormlbmu4 52030l umnaal iented perpendicular to a 1.5-T magnetic field. The loop is rotan40ll 5 bumu2mm a0la3ted so that its plane is parallel to the field 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 s sgmv(gw*eh, );e,figa6fc f4o 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 pointing down. What is the average induced em 4ghgwaef ifs,ef6(c,)v; gm*f in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of wire is p)mqi: c-z ukm3laced 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 increased, whz-b gs/ xxg39aat is the xg 3zx9s bg-a/direction of the current induced in the small circular 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 circu6 n2w3rt*ugs +3o j)evcymq:nlar loop due to the current shown in each partnoqt+2 vsy3rn ejw 6:)3c*gmu 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 be6 f;(*ve jn-6w(w yq-vovnfading pulled away from the loop shown, in what direction is the induced current in the lov( ;navv fq-(-j6ndf owe6* ywop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire loop 12.0 cm in dtaj(xb s 8+2)hva(ssj iameter is changed from +0.52T to -0.45 T in 180 ms, where b s(2htss)x a(j +jav8means 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()twa; fa4eui7s1 quf cm long and is pulled at a speed of 15.0cm/s If the magnetic field is 0.800 T, calcula;ws iuffq a(a4uet1 7)te
(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.zih(v i xy59qq/5k pr;75-T magnetic field pointing into the paper. If the (r5q/y;ipz ix5khq9 v loop’s diameter changes 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. Below)is 13x0 r;z5dh fw:nl .t 9yhd8mil /nj71mo.2 cm long and generates an emf of 120 mV while moving in a 0.9jhlw/ hnr8olmt 10ydz;m9f7d.x n:5i 0-T magnetic field.
(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 dimenln2pq poqj+(e.ybs+q* cidzb8 ; 7r2n sions shown in (Fig. Below) is situated inside a region of uniform magnetic field of 0.550 T. The total resp d.n++pc lsbqi8* ( n;7br22jze qyoqistance 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 diameter of 2.5 cm7io4o )lhw /in. A 10-turn coil is wound tightly around the center of the soi7o win/ 4)lholenoid. 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 moves with a speed of 1.6m/s is 30.0 cm long, and h10e /dq.nzpcrou pp- :as a res -p.qe pz /0ducrn1o:pistance 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 2.6 mm;l* qb jrbf;rddus/- ) in diameter. A u;j brb*lqs-d/ ud;r)f niform 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 perpendicular tog-np ghr+9 4(kq -iz yybgca:x24bnc1 jp)/zp 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 move4q yh1g(/k:ig cgb4znp2 a9jpzpcx- +rn yb -)s past a point in the coil during this operation?    C

  A simple generator is used to generate a peak output voltage of 24.0 V. Th oecfnut3 z7 1 sys,5r6z0d25mq xki;oe square armature consists of windings that are 6.0 cm o ;oi1c6mq0s 3o u52sz5dnze 7,rxtfkyn 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 ca;3 *lq3e 4 gsqhyihpz/ v19plcr idling at 1100 rpm produces 12.4 V. What will the ou tput be at a rotation speed of 2500 rpm, assuming no*e l943pgv3qz1 lyq/sphci ; hthing else changes?    V

Show that the rms output (Section 18–7) of an ac get57*az 7zc sdnnerator 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 j.bv2bir)rt9jws11i ks.d 2o on a side. How fast must it turn in a 0.650-T field to produc9ivdj j1)r2tor.isb 2k.b w s1e a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil (cacqvcc 7 (1v/pcrsf7b ov-llg1z-t btx- 7-with a diameter of 8.0 cm rotates at 120rev/s -(/cz-l1cx ts 7o(vcv - acqrg17c t7 lfbpb-vin a uniform magnetic 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 magnej: ket ,dvlir cg710.dvn 00sdazz4*we30ooktic field of 0.030 T. It has 1000 turns and produces an rms voltage osd, d17 t3rv0cdne0zw: 0kvoljgk oz4e *.a0if 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 armatua+wd08jeajr92y 3 gexre resistance 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)zz.ekavn 8u2 b mk;d( rpm. What would be the back emf a)aemn( zz b;82 dvukk.t 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 mp.wlq:m xjv 7a0nm67 would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the motor was ru7plm0v 7qmmx6awn:. j nning at 2500 rpm? reduce the magnetic field to    % of its original value

  What will be the current in the o1s1k-ts+oxd n-,lu emotor of Example 21–9 if the load causes it to ruo,1sst u--l1k dx no+en at half speed?    A

  A transformer is designed to change 120 V into 10,000 , hpjirvde cz2oq; 6:l+khr1(V, and there are 164 turns in the primary coil. How many turnshdi (,pl okq;2r6+ czvr je:1h are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 1k)jr*mpe:s. ; mfq0ydm(gm , +*jzpc/; chvar20 V. What is the current in the secondary coil as compajp q*.a +rgrfp(/v 0z)m; j ,ehmm;ccyk:*mdsred to the primary coil?   

  Neon signs require 12 kV for their operation. To operate from cm /m1dc 0,i2epkrc-y a 240-V line, what mu,2 rk1m0pccy/ec idm -st be the 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 128 egay72rjgswky*n,; 0-V ac and draws 0.35 A while supplying 7.5 Aygj,7w8yeak ;g r *n2s to the 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 trar4*3amtqsp ,a nsformer is 12 V, and the input current is 22 A. * rp4qmtaa,3s
(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 ijhb j-hhk+u- (2 pnggy,gu91 input voltage is 120 V and the output current is kpigh1(-- +hjy9,2 guh jnb gu15.0 A. What are 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 kp2c eh/p3q mm2mt 6.idV (rms) arrives 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 town xzs ,f-vd s;m-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 t u-sgknt5)8 lwgubx+ ,o 10.0 A in 350 ms, what i gwul-xbsgt+5k u),n 8s the magnitude of the induced emf?    V

  What is the inductance of a coil if the coil produces an emf of 2 z2d(8iix;ho0.koo vk .50 V when the current odh.o(8iv20 kxk;zoi 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-f*;nj)ht(x s bpilled coil 2.9 cm in diameter containing 10,000 *(sntjh bx p);loops?    H

  How many turns of wire would be require44(bffdxsytl / (h0o md to make a 130-mH inductance out of a 30.0-cm-long air-filled coil with a diametes4mhx(d off4/ ( byl0tr of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and ivhbd9ig3-n (aqh8 5dml*)s uvt is 2.5 cm in diameter and 28.2 cm long. vgu 935-dhq(nav l*dib)8smh
(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 a aprkzq:*:s5qnd 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 wounw td94-m t h/*rmegqq1d solenoid is unwound and used to make another tightly wound solenoid of egrqqwtm9d */t mh41-twice the diameter. By what factor does the inductance change?   

  The magnetic field inside an air-filled solenoid 36 cm long and 2.0 cm in diame l0s1a /pe mmak45(rsgter is 0.80 T. Approximately how much epmms1kl5(/ga 4era 0 snergy is stored in this field?    J

  At a given instant the current through an indumo-9b1n2myaajv v cw8**q +adctor is 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 known to be 60.0 mH, and hov am2q -c vd8a*o9*yaj+mbw 1nw 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’sp/m) g:t ms2g+: ghteh magnetic 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 currentp wjo:n wp-,(y in (Fig. Below) reach within
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoids h.u71:c 2a2-zvrsh-xqig e wj cave the same length and circular cross-sectional area. But sr2s jwxz2. -aqcu- c vhe:1ig7olenoid 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 reactanc50m-rk) xvu gqe 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 inductoronnlnc.ig4j, eq8 / 5ua gk4mdr vt*:7 have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will 6aw k7h.ey(d ) jpz(o(s)jk yhsczez3 8:3nfra $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the rc9ao j,m,z,.iamzm +,resix0 eactance of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reacu),ul 94jzbh9 ms:el3 yw+y wctance of a 1.0-mH inductor as a function of frequency from 1j9e4b: u,w3hsly9) m+uyz lcw00 to 10,000 Hz.

  Calculate the reactance of, and rms current i5uq2qyaz*b0 in, a 160-mH radio coil connected to a 240-V (rms) 10.0-kHz ac 2za biyqq* 50uline. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 6 nkq0s-jvy,9yh8 q;r f0.0 Hz. It draws 12.8 A. What is the c 8,9 qyqk h;0r-svnyfjoil’s inductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a well-insulato6jdc5/h) kah ed $0.030-\mu F$ 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 passinvu ol;( ckat,4g through the human body for 1.0 s could,;taklo (cv u4 be lethal. What must be the impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance oclj wil+gb4o8 (,ab k)q+r;(qd6p nqmf a coil if its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, anwcqv5 /k0wg0zl3zalnx4i d* -d rms current in an LRC circuit connected to a 10.0l c3x4a q*0gwin/z5d w-lvzk 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 inducnmr,,9kjwv 8 7vjxp *ctor is driven by an ac power supply. At what frequency is the impedance double that of the impedance at 60 Hzjvk,wc, jm98vr n*xp7 ?    Hz

  (a) What is the rms current in an RL circuit when a 60.0-Hz 120-V rm1enaj1l+++eyisi hd 8s ac voltage is applied, iaje d1+8ieylh +1s+n where $R=1.80\mathrm{~k}\Omega,$ 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 8mm1m 2di9xu0qg93ts9qfrof ifwy ;* 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 connecx v1j 5+qixcd8ted 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.30fj 1xhf/yt,il,h 76,axj qgghwnj AM radio has a capacitance of 2800 pF whe7h/ ,xhf6t.xl gj h30,w gjqanf1,yjin the radio is 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 = 14.8 mH a) dv+w6- w 6(qombktodnd $R=4.40\Omega$.
(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 loopsq*k 1u+ty/k1 7u2wl.fstnemp in the plane of the page as shown in (Fig. Below). When switch S is thrown in the left-hand u7ufelwknp/1t +.t 2*ksmy1qcoil,
(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 resistance ofbc)n3vm5ckf7y y 5rw) $5.20\Omega.$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 y84d0/uxx:mzky+z.avhc +jois rated at 45 W but requires only 12 V. It contains a transformer that converts 120-V household volto8 zdxa +.zky/m0yvh4 c+:x ujage.
(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 2- . mq jmuni3tc.f+ls(4 kV at a generating plant located 118 km from a town that requires 50 MW of power at 12 kV. Two trqm(+j 3 tu.-nsli .cfmansmission 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 transformer which has an 80% efficikx+ia,am 8*kcency are connected to 110-x iakm 8+a,*ckV ac. 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 linesn x/cszfipwd5e ( iy77q8/hd qt1:;wp 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 3 mu-1s g,wut6bcj f(y+2 cm apart 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 loss fg(e fn e9w(b oyb1z.ty3 f-x,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, a radius of 5.0 cm, anzxga 6 +e /cfhg-84qvvd 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 agai)p71.kd1vo mloqaw- 0ai au 0mx 0rb,snst sudden surges in current. In particular, after therka0avb-u0.7a1pm mw ds0 )qix1, loo power is turned on the current should rise no more than 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 between the pole pieces of an electrx*w ,y z+x(fv/9cenzcomagnet. When the magnet is turned on, the flux through the coil changes, inducing an emf. At what rate (in T/s) must the field produced by the magnet chax/xe(cznw*9fv, y zc+nge if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simple generator whoci)6:wuzy e;u;afi/ j se square armature windings are 6.60 cm on a side; the armature contains 155 loops and rotatezc6uj;ai: );wfiu e/ys 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 lpg22b:tk3 d ri 0q/zu0grsl6 laboratories are 2z/3s0t gir0k l u:pblrg62 qdabout $1.0\times10^4\mathrm{~V/m}$ 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 vfgm q.*g)i;p L of the primary of a transformer whose input is 220 V at 60.0 Hz if the vm;.*f )g giqpcurrent drawn is 5.8 A? Assume no current in the secondary.    H

  A 130-mH coil whose ;bkw0v0q2dyoao a*z9 reeg.,resistance 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 conng082cuf,b c l2g *kp vdc )tap/(m8saxected to a 60-Hz 120-V (rms) source, the current drawn i2sk,8 b2f cc*ud8vl/tgxa(apc0) gpm s 3.8 A (rms). Determine the inductance and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor wi2m qsw3ye +.tbth $2.0-\Omega$ 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 define* vq*ir:zjxaiq7 q3+; uzw a9fd as the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. Thq*r7aq*qfu; 9zzij3a i v+wx: e 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$