What would be the advantage, in Faraday’s experimejk;pl1p/8yw (c iu ph+nts (Fig. Below), of using coils with many turns? w+ku8/j;(yp ipcl1h p

What is the difference between magnetic flux and magnetic field?wi)z:52u3fd47rqt vqe(bk *swdu f3k

Suppose you are holding a circul gys 3sk+q*j6ear ring of wire and suddenly thrust 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 +eg*js yqks36 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 movi(qzrw9-ffye2.n/qly /nq2 qv ng in the vicinity of a very long straight wire carrying a steady curr9 qqe/rwnzvq y-nf /yfl(q22 .ent as shown in (Fig. Below). Find the direction of the induced current in each loop.

Suppose you are looking along a line through th:rz cww 0d(fs-e centers of two circular (but separate) wire z:dwc(-0 wsrfloops, one behind the other. A battery is suddenly connected 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), determip pk v.70ex+2 yayk,4s*nw2 u ehxwh;xne the direction 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 “shielded caz44;( pl5) k qifqbpyhble” is used in which the signal wire is ( lykq)qfz ;hp4pi45b surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return current. Why is a “shield” necessary?

What is the advantage of placing the two insu) /y;r ;/o4deeudmw wqlated electric wires carrying ac close together or even twistwde)yr/e;;4 uw/om dq ed about each other?

Explain why, exactly, the lights may dim briefly when a refrigerator motor sta pf4* 75us0e1 r:unrp7nncuscrts up. When an electric heater is turned on, the lights may stay dim71c7rp5 usprnn*sfc0 nuu4e: med as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hand rules to show why f)8gvnlvf z,s2 j h(+vthe counter torque in a generator oppolf(v vz f+sn,vh8j 2)gses the motion.
a
b

Will an eddy current brake (Fig. Below3 t*m wd27mtg3*dnfu e) work on a copper or aluminum wheel, or mum u *e dn2g3fmwd7*t3tst the wheel be ferromagnetic? Explain.

It has been proposed t,6y v v5gva2im8 z *vrhjj;x,qhat eddy currents 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 inzxv56mh,v;*ivv2ajygq 8jr , the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quickp;.w,nf q2gnf8w)6z s -lbabcly through a magnetic field than doesw2aclf;b6n q.wzbf8 g,n)-s p a solid bar. Explain.

If an aluminum sheet is held between the poles of a lar55dnuznya ik3p*act75f. k4c ge bar magnet, it requires s5uz4a*.kncf ak35ct7 dn i py5ome force to 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 reaches a terminal velof3 8)vowxqs(x 2:hbb,3;e9zn d wu nvrcity even if the tube is evacuated so that there is no air resistance. Explain.u8 zhwnwq23e :nr(;)9xb,db sv3xf v o

A metal bar, pivoted at one end, oscillates freely in the abse23tc l 0djdegv,r*q,dvxp;0y nce of a magnetic field; but,*v3dj,x c0d;p tvyqdlrg e02 in a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical devices.)

An enclosed transformer has four wire leads coming from it. How could you deter2hnogifje nx:+q;z 9/mine the ratio of turns on the two coils without taking the tf+h9x; nz n/j2 eog:iqransformer apart? How would you know which wires paired with which?

The use of higher-vo0:xix kys eh88ltage lines in homes — say, 600 V or 1200 V — would reduce energy waste. Why are they not useyi0hx 8kex s8:d?

A transformer designed for a 120-V ac input wx1w z3(+ igok6rlm6gt ill often “burn out” if connected to a 120-V dc source. Explain. [Hint: The resistance of the primary coil is us3g61 zlk(6oxgt wim+r ually very low.]

How would you arrange two flat circular coils so that their mutual inductancz5 .0/4/.magjbu t.z xizea /oyti4tze was/g.tja4b exy .a /z .ztu4t5m/oz0ii z
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the batteu6c:yg 1;x lpory in (Fig. Below) affect the time needed for the LR circuitxc61opy;l :gu to reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, clb8xcpqzu:.b- qx,5t an 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 t 2 nebwcvb.k:9 dm3qb:y-ez9cg 4p:vfrequency of 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 the impedance in an LRC circuit a minimum.6 rlg-pn+ hd lr+j/n0hqu p/i vb.yy2(u 0xi*o

  The magnetic flux through a coil of wire containing two loops changes from -51h g:sge2eiu ;0Wb to +38 Wb in 0.42 s. What is the emf induced inehe1si: g2u g; the coil?    V

  The rectangular loop shown in (Fi)q/we e1an5:wz *gdmxg. Below) is pushed into the magnetic field which points inward. In what di g5*xn):qw 1eezwmad/rection is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the mu9stn0p (*po ;adn0htagnet in (Fig. Below) is being inserted into the coil. In which directi sothnu9a(;pp00 t*dnon is the induced 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 1.1ksb,sf;k 5sac,b:bq fxp 58/d 0-T magnetic field. The loop is removed frkf sfap,b5xq; b,5bcs:/sk d8om the field in 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially orienm6j 8)l5fjqg/xza s *ybd1 u0qted perpendicular to a 1.5-T magnetic field. The loop is rotated so that its plane is para6g80jzb dqly 1 jm)s*5/xquafllel 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 orien u2,h6vq t5lihted so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the coursi ,lqv2th65u he of 0.15 s, the field is changed to one of 0.25 T pointing down. What is the average induced emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of w3uul*b4qgh r;m;yp 5vire is placed 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. B3lz zy9-* triaelow) is slowly increased, what is rzia3l*-9 ztythe 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 indu e zi)i 7+44zjwjo5boxced current in the circular loop due to the current shown in each part of (b ji7zzxjwoi+45 o4e)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. Beo rahae/- qa65low) is being pulled away from the loop shown, in what direction i6/-o5eaq aa rhs the induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circula* nj7p*h te4th83zudq pftv0 7r wire loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the field po80tt7 t47 *fdjq upp hh*v3enzints 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. Be ge0vbz8:;l 5.4,p ht;kellsi x3kshclow) is 12.0 cm long and is pulled at a speed of 15.0cm/s If the c,s;gl;0l3i k z8h :t4s .kelxvbpe5hmagnetic field 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 thde vebl*)(dfue3)w5 t e plane of the paper lies in a 0.75-T magnetic field pointing into the paper. If the loop’sv)eb e*( )lewfdt ud35 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 13.2 cm long and generatesum5 e )b fije5qd3n6xb0rs,:e an emf of 120 mV whi535eq s bbxim:e0r, uf6j nde)le moving in a 0.90-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 dimensions shown in (Fig.gz2gup(bpi .ct324 s u Below) is situated inside a region of uniform magnetic field ofst2b cp4 zp.2guiu (g3 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 cmkvdwb;i,ldb)9fxioag. .z8q(l jty0 p- p *5r long, has a diameter of 2.5 cm. A 10-turn coil is wound tightly 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 durinlv.-dgqbkjo ) *(59dltyabwx 8pi.z; ,ri0pfg this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves with a speed of 1.2dhq e;)0, 8eo pm+frxdwc yppn7-/ie6m/s is 30.0 cm long, and has a resistanem - 0; rxpqwop,nd/+)82y7cheeidpfce 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 xh.,,vq0 s5r yfhk znn **7pwt-1ekni turns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the c 7v,nkzik n.npw*h,sxqt*e f5 r 01hy-oil, 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 to a single 13.2-cm-diameter circular loqur2;*ixy:fido (dt 0 op of copper wire decreases uniformly from 0.750 T to zero.ur2yii*0(f o dx;q:dt If the wire is 2.25 mm in diameter, how much charge moves past a point in the coil during this operation?    C

  A simple generator is used to generate a peak output voltage of 24)u(,aoya t dmnt)jjo y*qv,n*do64 v4.0 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/n v*monuod4 jtytj) 6(*qa,v4 ad ,)oys How many loops of wire should be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idlingssw6 xo90eq (i i(dfz+ at 1100 rpm produces 12.4 V. What will the ou tput be at a rotation speed of 2sed (f60ioq 9wxzs+(i500 rpm, assuming nothing else changes?    V

Show that the rms output (Section 18–76jjs-qky kq sa)327uj) of an ac generator is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop squar+(hmza/ r4etneqh:.;x0k+ j 1 uixtkw e coil 21.0 cm on a side. How fast must it turn ix;xkq/.+hahtku wi4 +t:n10j( zr eemn a 0.650-T field to produce a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil with a diameter of:5* menaqin 7l 8.0 cm rotates at 120rev/s in a uniform*qlin7na5:e m 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 magnetic f5:(8s e5gnfupf, tfgxis, . yvield of 0.030 T. It has 1000 turns and produces an rms voltage of 150 V ay,fsf5vg.f 8ps(t5e,g :xn iund 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 resistance oy+l o t lvephc6 dp+l5)9(mgk2f $3.25\Omega.$ 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 w8nzly vn wzp6*r ypeh*3q2 k9-hen operating at 1800 rpm. What would be the back emy 8wv*kn 6z3-yep h rqpl*92znf 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 woro(x/ ye p8km8uld you change the motor’s mae k8yo/r(xp8 mgnetic field 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 Example 21–9 if the load causes it nxx;vs 76ws/d .a(eplto run at half xvn le7.d/( ;wp ssx6aspeed?    A

  A transformer is designed to change 120 V into 10,000 V, and t, gyalq;p d9lbx.+ zhi93gom/here are 164 turns in the primary coil. How many+z.l pm,aigoqbd9 gl;9 /3 xyh 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 web le6e*g 9iy +m9h*kthe current in the secondary coil as comparg*hkey+wi* e b m9e69led to the primary coil?   

  Neon signs require 12 kV for their operation. Th; )jj8x8jmfe o operate from a 240-V line, what must be the ratio of secondary to primary turns ofj8ex;j hf j8m) 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 0yr eeg1so/a: e3dwt 38.35 A while supplying 7.5 A to the trar1w8g oed3ae:3st ye/in.
(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 isa1e,ygvj0e / krp s9/h3j1n1mf:qljd 12 V, and the input current is 22 A. 1s mr /yaj9p : fdnqj1,g3 k/jeh10vle
(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 c6tbf3 vz-e h5q*a3s:lgfjm at -)n ;zand 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A. What are the output voltage and input currentlz-f3jbvzma:-g* )6hqa;nc 3t f5 set? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =    V
$\frac{I_\mathrm{s}}{I_\mathrm{p}}$ =    A

  If 30 MW of power at 45 kV (rms) arrives at a town from a generator64q/b5 ( zd d5gnoafzp 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 trs +zg 8hwtlwx8)/epe7 -b5ceown 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. db h++xoj)h5g0 A in 350 ms,b+5g )dhxjo+h what is the magnitude of the induced emf?    V

  What is the inductance ebz0o l2::f mpl(5yeh of a coil if the coil produces an emf of 2.50 V when the current in it chanmz b l5fho2(:e:le p0yges from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-m-long air-filled coil 2.9 cm inzzyc2. vst,x3 diameter containing 102t. cys3vx zz,,000 loops?    H

  How many turns of wire would be required to7vf jly.cfixnqpe g (43i4,;l make a 130-mH inductance out of a 30.;fj7ipicvl g fn4ly 4qx. ,(e30-cm-long 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, and it is 2.5 cm in diameter / .7zau5jnr)3es dnzaanu rn7/zea) ns.da5 3jzd 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 cross-sectional area A conta3mia mzkh, tbj5+b)1qins $N_1$ 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 o* ab ato;a.wiq ounz *,;cvw ym4)c0+used to make another tightly wound solenoid of twice the diameter. By what factor does the inductan z*q moio,o4wv+ wtaua;n) c.*b ;0yacce change?   

  The magnetic field incqheaf;2a 4 b+side an air-filled solenoid 36 cm long and 2.0 cm in diameter ifca;ha 2qb 4e+s 0.80 T. Approximately how much energy is stored in this field?    J

  At a given instant the current through an inductor is 50.0 mA and is increasing7hkvvns z(b0s/4/ekg :d/2- i d egckg at the rate of 115mA/s. What is the initial energy stored in the inductor iv/(gh-7dg 4sg sk/ kzbke:i2nde /0vc f the inductance is 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 magnetic field averages abok, .rd hdjqq zd2mobqs,: 6.xqo9uw2 :ut $0.50\times10^{-4}\mathrm{~T}$ 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 q:yaux8a a3xzai +u) 7the 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 the same lengtnyq)*j l7jlccrrjf(9si u / .-h and circular cross-sectional area. But solenoid 1 uses wire that is half as thick )y9(*cuj.q j rl7cr/- insljfas 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 (pc/bi cf i9qb,:q3llof 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 reacta4td)v 4iq /bjrnce of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will . ikm21m jv+upa $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance oisxd4:dlo3v (f 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-mH inductor as a f1 ,z3cjxbfo.gzysm 0 l+mf2b* unction of frequency from 100 to 10,00.zy 01*+ mzfblxs,jf3 gc m2bo0 Hz.

  Calculate the reactance of, and rms current in, a 160-mH radio com../wax zjcpc66 ol.ib3m k4hil connected to a 240-V (rms) 10.0-kHz ac mjk.63pzch6a i. mo.wx4l b/cline. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It draws 12.8 A. Woyy6( e;gy -b2zv xcb:pf2,q nhat is the coil’s inductancen q:evyg;by2(pzbo, cyxf6- 2? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the react o/l0 sib1.khepx2 )v6nqz*lcpyh,u)lh9 vy) ance 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 voltage, an rms current of 70 mA passing through theq/ g.f44-d/ckmt ivrz human body for 1.0 s could be lethal. What must be the impedance of the body 4crv/ t z.4i- /gfqmkdfor this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if itsc hs3lg v/g(sdxce9(( impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, 4zbvxnf:i ( 1c*zt 1kephase angle, and rms current in an LRC circuit connected to a 10.0-kHz, 725-V (rms) source i*e:4 bvxfz11zikc ( tnf $L=22.0\mathrm{~mH},R=8.70\mathrm{~k}\Omega,$ and
Z $\approx$    k$\Omega$
$\phi$ =    $^{\circ}\,$
$I_{rms}$ =    $ \times10^{ -2}\;A$

  A resistor in series with a 42 6j;6vlv k bbz:;y. yo;0silqppik6l zr03 -er0-mH inductor is driven by an ac power supply. At what frequency is t3r z;zrl0 e 6yqlpsb6 ib;0vy- :ij6k.lkp;vohe impedance double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current ipyi( 9 zb0 w,)y*qrlczn an RL circuit when a 60.0-Hz 120-V rms ac voltage ii(qzybcl09, rz p) *yws applied, 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 in an RC cif wdg2p*g 0y/ircuit 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 isgez. 9 ozep,-j connected 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 0 no//.5xd dnfjekq)r 2800 pF wher)x. fjd/n0o d nke5/qn 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 a92 - i4uhl)tljm,wgb+p9 btound $R=4.40\Omega$.
(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 the page aa0i, di s-q6bpswa mp9i05t2ps shown in (Fig. Below). p,w0ppsa2msd 0 a ib 9it65-iqWhen switch 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 resistanv j-0v3u(li:;j4knp b iyd p:ace 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 at8n )dxkx5y1yv 45 W but requires only 12 V. It contains a transformer that converts 120-V householdvy8n5x1x ky )d 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 plfz. -v5yq y9pfue+a7fj6/lu9mymd u*ant located 118 km from a town that requires 50 MW of power at 12 kV. Two transmission lines from the plant t9y f 9mq.+vaz7f m5 jy-/dfu6pluu*yeo 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% efficiency are connected +,/au:psml .zfuyi:a ce;)vs to 1::;, z uie cpy smf)vls.ua/+a10-V 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 p5(g6m w: pav838p af tqi0(h n:bdxzelines 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 cmnulna92hpx +- 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 in transmission lines, 2. y(ha,proyw,ay t1s$R_L$ 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 radiusv0zl87l0sc8al+uew ydh*k e0 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 against sudden rj11esrm7 bvo bv1o1o sema.q861ws. surges in current. In particular, after the power is turned on the current should rise no more thro. vremjbvb1s. 7 ooe11s1 was16q8man 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 an5dxr ss b,b3g2n ;q7*eish1gd electromagnet. 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 ihx5d2ng rbbe3sdg7 s ,q*1s;change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of l) ;f2mpu (hxk8 4qfylf w p4;s: s-6l;tthhjca simple generator whose square armature windings are 6.64sh4fy) w(6tkcm8 pxf: l2t lls;;qjh; hpu-f0 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 at* d76t ofw3y rj7)vesotained in laboratories ato *d )orsjf76vew y37re about $1.0\times10^4\mathrm{~V/m}$ 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 is q pzv:,dgaa5ku fu+ ngs8se ;);.n yd:220 V at 60.0 Hz if the current drawn is 5.8 A? Aszp, syqau:; k)nfvgs.:5ng8 + dd;eausume no current in the secondary.    H

  A 130-mH coil whose resista(l 2**k2qiy77 bye l djxcl0zznce 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 x;ql qs0s ,vf: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 inductance sfv0; ,lxqs:q and resistance of the coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor wim wwnj q,dmf744nb b0.th $2.0-\Omega$ 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 circrfx -e n;/*1ism cwq-juit can be defined as the ratio of the voltage across the capacitor (or inductor) to the voltage acros1;n* r/i wjme -xqcs-fs the resistor, at resonance. The 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$