What would be the advantage, in Faraday’sjs r*:8yk by9goi)w 1j experiments (Fig. Below), of using coils with many turns1y :or*yiwb 98)jsjkg?

What is the difference betwee(jcyb 75 ;fax.qf4bdcn magnetic flux and magnetic field?

Suppose you are holding a circular ring of wirrherhk0kd1 0-uhe f f590s(mu e 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 magne1 dur 50e9hfsmkh0re-f0kh( ut 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 wire u 1jdder osx6+/ul v-k)--kdwcarrying a steady cu)dds xvr-+ u--lujo6dew/kk1 rrent as shown in (Fig. Below). Find the direction of the induced current in each loop.

Suppose you are lookinp*)b 5zf smr+wg along a line through the centers of two circular (but separate) wire looprf)+wb *p5zms s, 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), determine the direction of the induced current in resistcd77rehky. g29(o ondor $R_A$ 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 cabtuv2.- utf ha3le” is used in which the signal wire is surroundet.uu 3vahft2- d 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 insulated zb5) z)du1e8 9hemgkwelectric wires carrying ac close together or evenw)8m)hude5 1 kbze gz9 twisted about each other?

Explain why, exactly, the lights mayde2 4bve ;a/5pqukpg9 dim briefly when a refrigerator motor starts up. Whep5u/ 2adkv4;bqg 9p een an electric heater is turned on, the lights may stay dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Below b) plus the right-hand reu a+q3uppw(l2 bl64 eules to show why the countl weq+a(e bupl63u4 2per torque in a generator opposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper or aluminum wheekw 8pyfa93ro (08jgu ul, or must the wheel be f8gyu(9for 03kjp a8 wuerromagnetic? Explain.

It has been proposed that eddy currents be used to 6ssv o cxt:1;thelp sort solid waste for recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to slide down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) f tssc1 o:vx;6trom nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quickly bm:qhkbxs/m i7;9xu -through a magnetic buhm-/ bsk:;9i7q xxm field than does a solid bar. Explain.

If an aluminum sheet is held between q,.rxva -8vdeq0o ja4 the poles of a large bar magnet, it requires some force to pull it out of the magnetic fielx qq,8 rvve. 0o4ajda-d 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 termiap/luz ow4j.*ze+l*0j l 8jwjnal velocity even if the tube is evac40w zwjju8lz+ /*pajjl .el *ouated so that there is no air resistance. Explain.

A metal bar, pivoted at one end, oscio0wvtb /-3l4y ps27qux q wpn 0g.wc.wllates freely in the absence of a magnetic field; but in a magnetic field, its oscillations are quickly dampedwl 0wb3pc -4toyqpg2 7 usq.wvxw0n /. 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 detkg3 0 da5li (wrrmua ymc16eu-b7yk5 5ermine the ratio of turns on the two coils without taking the transformer apart? How would you know which wiresd6wk-(ubc5y1 0m53r7u rim a kle ga5y paired with which?

The use of higher-voltage lines fzy71 uc (ke)ain homes — say, 600 V or 1200 V — would reduce energy waste. Why are they not used(zf)ua7 yeck 1?

A transformer designedx 1,e8fvjjb0lyyl 9s54fvo0 v for a 120-V ac input will often “burn out” if connected to a 120-V dc source. Explain. [Hint: The resistance of the primy, xfolv1 y8j9lsvf 504ejv0bary coil is usually very low.]

How would you arrange two flat circular coils sos rwe 1 ztr,s7,5bey;p;m(wk e that their mutual inductance way;s tew (zm,ee,wrb ; 5kpsr71s
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battegg*yfh611u zdsdj m6 t wd7.3lry in (Fig. Below) affect the time needed for the LR circuit to ret1h6 d dyjw.3gd1 sg*z7lfmu6ach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltage ac(9vn5 -urrzzp ross
(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 impe:ro u/q9q y s0icpa9k)vccw22dance 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 impedancg i )rayj wea-55zg-v.e in an LRC circuit a minimum.

  The magnetic flux through a coiht(3wn:pjoiepx a1 j-/ li9 f//zp;f dl of wire containing two loops changes from -50Wb to +38 Wbd lh3/x1t/p:o n/ ;za jwi9fief(-jpp in 0.42 s. What is the emf induced in the coil?    V

  The rectangular loop shown in (Fig.f /8 y(csz0bjvd)0vv8 cak6oq Below) is pushed into the magnetic field which points inward. In what direction is the induced currdv8 yacvs()k06z8cbjfq/0 vo ent?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fz6xj,-g zh9ihm-gsh :ig. Below) is being inserted into the coil. In which direction is the induced current flowing through the resz ,9sgz6 mhjx-:-ih hgistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wire is in a 1.10-T magnet o r.bt zdtdc++cx11:fic field. The loop is removed from the field in 0.15 s. What is the average induced embx+.t+ tr dccz1 ofd:1f?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is initially orie,gw t zhw.l0,wnted perpendicular to a 1.5-T magnetic field. The loop is rotated so that its plane is parallel to the field direction in 0.20 s. What is, t w0gw.,hwzl the average induced emf in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially oriented so that its plane is 2+v+, q/s bvrcn-tgqs perpendicular to a mtgqv ,nq/sc+sr-+2b v agnetic 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 emf in the coil?    $ \times10^{ -2}\;V $

  A 15-cm-diameter circular loop of wire is placed wcvyp0e; m( 49j9ohvvin 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)poi lkzopvc7 (sd)* -y/qoef.3 swy5. is slowly increased, what is the direction of the current induced in the small cirlppyi.- 3 yos f.z7d)ws/5*eq(ck ovo cular 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 c d-c( + eiylm,k:7fh5 5przzteurrent in the circular loop due to the current shown in each part of (Fr,mik5ht+le-7 fd y:5z cz p(eig. Below)?
a  ----待选择----counterclockwiseclockwise0 
b  ----待选择----counterclockwiseclockwise0 
c  ----待选择----counterclockwiseclockwise0 
d  ----待选择----counterclockwiseclockwise0 

  If the solenoid in (Fig. Below) is being pulled away from thuzc ,zc;uyxu27y/4jle: 4 x/ m9jmg7v2 qvcwre loop shown, in what direction is the induced current 29u ;jv m 7 cz:c vx,yx4/2umwqy/jzu7lcer4gin the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire loop n vyb za:3d3*z12.0 cm in diameter is changed from +0.52Tb:d3n*vyz3az to -0.45 T in 180 ms, where means 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 and is pulled at a sba9)2 a/*tx-+l cswax .6ks3sx zqifcpeed of 15.0cm/s If the magnetic field is 0.800 Tt6/xs k*ifzq-9 a lac 23c.bas)xs+wx, 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 ther 8ui3rk-e a*ydefs+ b+v5k)c/re ao . plane of the paper lies in a 0.75-T magnetic field pointing into the paper. If theeeuasc5 8e+vkr +fka)i* 3do- br.r/ y 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 13.2 cm long and generates z)s8y+l9 bh1gv-nb;, tc q:weppzxl 7an emf of 120 mV while moving in a 0.90-T mag e+1pg:y-)9 pcl8l,s7vbnbxhz t wqz;netic 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. Bu -1 lxd9o8c0 bz9wgh .czf.jgelow) is situated inside a region of uniform magnetic field of 0.550 T. The total resistancw99zf- hz.oc dju0x18ggl.bce 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 cm. A 10-turn4 qx9o,3t znig6gu by. coil is wound tightly around the center of the solenoid. If the current in the solenoid increases uniformlig3q 4, unxt.boz69gy y 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 rog2*uwk ; z3fc4ggn r2fd moves with a speed of 1.6m/s is 30.0 cm long, and has a resigkf4u2;3r fng*2zwgc stance 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 20km- 4:.,swjm4 ppjyab n kef.8 turns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the ck -w4bf p 8j,ma:e. ysn4mpjk.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 siz ahh/ fgh6wuky/k 8i;u./o+dngle 13.2-cm-diameter circular loop of copper wire decreases uniformly from 0.750 T to zero. If the wire is 2.25 mm in diameter, how much charge moves past a point in the coil/6azhh;y// kuhk ou8fg + di.w during this operation?    C

  A simple generator is used to generate a peak output vz-wtrm*h(sk+.5aw dk oltage of 24.0 V. The square armature consists of windings that are 6.0 cm on a side and rotates in a field of 0.420 T at a rate of 60.0rev/s How many loops of wire shou hrzk.+*km5w wtd(s -ald be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 1100 rpm produces 12.4 V. 5i7eza8 m(*+ vs fgypvWhat will the ou tput bsymv7v( z+pi8f a*5ege at a rotation speed of 2500 rpm, assuming nothing else changes?    V

Show that the rms output (Section 18–7) of an ac generator px2p k2pvu,n: is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop square coil 21.0 cm on a side. How fast must ;wb-,+d9n rkm ,dw zxfit turn in a 0.650-T fi nx-dbk;rz9w, md,f+ weld to produce a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coil with a diz5m(dcp 51 nr ,vbki(wameter of 8.0 cm rotates at 120rev/s in a uniform magnetic field ofc15d ( rw,kp5(b vnzim 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 fieln(bawj 69k-h8mvvy , yd of 0.030 T. It has 1000 turns andjy6avw bn-8yhv k,m 9( produces an rms voltage of 150 V and an rms current of 70.0 A.
(a) What is the peak current produced?    V
(b) What is the area of each turn of the coil?    $ \times10^{-2 }\;m^2$

  A motor has an armature resistancir v+pf r h7(n,5 kz42ikn5zsf(k2vut gnnd3,e 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,h2 onu,kwvvurfr90 l z, r(t7 at 1800 rpm. What would be the back emf at 2500 rpm if the magne79 rr 02 wtl,nv,zuu,hf(o kvrtic field is unchanged?    V

  The back emf in a motor is 95 V when the motor is operating at 1000 jvcnbhz65t dglx1m-eh * (64brpm. How would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the motor was running at 2500 rpm? hl v1-6ecx *5t6ghnmz4bj( dbreduce the magnetic field to    % of its original value

  What will be the current in the motor of Example 21–v8:.zd i bs- tpehj2x1 -k9hat9 if the load causes it to run at half spesk9dhh.z b2-paej8 -tt:xi v1ed?    A

  A transformer is designed to changeh(a.lh2w7n ut u+yfzs9dh5q2 120 V into 10,000 V, and there are 164 turns in the primary cu5 lsunh9d y+7h2f.z a ht(q2woil. How many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increasearl 6 fmkt+c.c9s5x/ys 25 V to 120 V. What is the current in the secondary coil as compared to the primary coyxt/k+a m.cc9fr56s lil?   

  Neon signs require 12 kV for their operation. To operate from a 240-V l p3pwla+e*; rfine, what must be the ratio of secondary to primary turns of the transformer? What would the voltage output be if the transformer wer r*+;pewa3lpf e connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer plugs into 120-V ac aree6mr5vd aku ,e) 3v4nd draws 0.35 A while supplying 7.5 A to the train,evr k 6 re)m5edav43u.
(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 current is 220 pdau+w8,wfb A. +w,bu8 dwfpa0
(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 ane,)d+ kxcdjsfwlq7aao 80 us0h:z i6/d 1340 secondary turns. The input voltage is 120 V and thex)h0jqc de7u k+l8oiw6s 0dz:/fs,a a output current is 15.0 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 kV (rms) arrives at a rd6ui1 ueohwxtb,50u/0d)em 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 o7 (2nx obbq*8 yv1vqenver 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(ov9gru,5;*tcl hcmfo 10.0 A in 350 ms, what is the magn9m hgrot(; *cl5fuv ,citude of the induced emf?    V

  What is the inductanc/zidp xf3ss4g 2g h6d */fbzqdpu: 9v.e of 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 12x:4gv9/p2f gb/ dqud6.s zs*dhzip3 f.0 ms?    H

  What is the inductance L of a 0.60-m-long air-filled coil 2.9 cm in diameter dkg50*k-tju (je)hm,:t d kygcontaining 10,000 loops0ketguk m ,d) (j*tyhk5-d:jg?    H

  How many turns of wire would be required to make a 130-mH inductanjcug w;64tsz(,q +n v(; zo/cesaps k5-ambj(ce out of a 30.0-cm-long air-filled coil with a diameter of 5.2 csajuq a+oe;z,bjks(g5;ncv6p/ (ts4zmc w-(m? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and ntdd (v wto8g :+;sat0it is 2.5 cm in diameter and 28.2 cm a +tdt(dgvn;o: s08t wlong.
(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 conta nevllh2) fh(t8h0n3fins $N_1$ 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 woundoed3s t ;euez4r) *tc- solenoid is unwound and used to make another tightly wound solenoid of twice the diameter. By what factor does the inductance chan*tcre3;ezt o -d us4e)ge?   

  The magnetic field inside an air-filled solenoid 36 cc2r o )epm+gvvdx 94 z+4o)e*ao+ lgrdd ry7k3m long and 2.0 cm in diamete+c)r *rao d+eomp)dk 4y ov z g2vd3lx+97gre4r is 0.80 T. Approximately how much energy is stored in this field?    J

  At a given instant the current throug1- mon6ea(k;-)q qb5 uz +vikmzzepm/h an inductor 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 kv65nmoik )zpqquke bm;/-mz+(a1 e-znown 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 e(uu:lh oiy) /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 does6x +5 ,au;y9rzxx on,8c9dkw 2tgzkmo the 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 length and circular cross-sectional 93w3 o3s ,euau hqggt)area. But solenoid 1 uses wire that is half as thic 3ghuaws 9)3tqg ,eo3uk 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 ofam6oj ,5;itb0:hii blb) vl ;x 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 of)w2uoclwe/;rcv zgw6jk)) 1 l $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will a kwq nosd+x*- ,gdo3xmk.-y 8c$2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance of a ,1 ziy-+e :w-rfnn see$1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a 1.0-mHf 7py*ltw7w *,5 ebt5md+c wlc inductor as a function of frequency from 100clf p+tb5d wwle*yw,7*7tc5 m to 10,000 Hz.

  Calculate the reactance of, and r1jphui 8 nno:7ms current in, a 160-mH radio coil connected to a 240-V (rms) i7j81pn hnu:o 10.0-kHz ac line. Ignore resistance.
$X_L$ =    $\Omega$
V =    $ \times10^{-2 }\;A$

  An inductance coil operates at 240 V and 60.0 Hz. It drawc vb6 n:f+/gfx* a7quau vx2)ss 12.8 A. What is the coil’s inductance? g nb fc)s /7v6v*u+x:f2aqaxu$X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a w(8 m w k2w9dyxfy+x0+ztapvw8(i 7b taell-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 the* j5oba8 b+tvk human body for 1.0 s could be lethal. What must be the imk* obj8v+a5tbpedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a +qq38-otp:jg)3blbearu.h 8 1 vgmm4tp.avy coil if its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, ank acn1) fm:.3sdxk l6mn75x avd rms current in an LRC circuit connected t5sf3kkvlam n17n)ax.c6 :mdxo a 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 series with a 420-mH inductor is drivef ifae6+-jcm+n by an ac power supply. Ac6mia++ff je -t what frequency is the impedance double that of the impedance at 60 Hz?    Hz

  (a) What is the rms current in an RL circuit when a 60.0-Hz 120-V rms ac voltagejlp3bvgotl/8 f w1uq(6lj 9s * is applied, where ( w plb63q /v1fjosgju *l89lt$R=1.80\mathrm{~k}\Omega,$ 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 inhzp3ra.)yay *c 6c)h c 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 connecttto0z*vr l*r45c lwv, ed 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 capacit*q y6ck9pqlgfr6 zctl 2r;8r *ance of 2800 pF when the radio is tuned to a station at 580 kHz. rfc*l6 6rg9*28 pyktqzlc r;q
(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 and q iqejp7qv h9bmvq3310 8mbxouv3(w.$R=4.40\Omega$.
(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 i;c9yh)r0t vaoh8ks9 un the plane of the page as shown in (Fig. B ;a09k)utsh rhc89vy oelow). When 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 s.wnubyn2c6y bx )f*b+ide has a resistance 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 only lmjo ldq ::,*g(b,dho12 V. It contains a transformer that converts 120-V household vohlg *:q o,(:dld bm,joltage.
(a) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer
(b) What is the current in the secondary coil when the lamp is on?    A
(c) What is the current in the primary coil?    A
(d) What is the resistance of the bulb when on?    $\Omega$

  Power is generated at 24 kV at a generating plant located 118 e6mf,v q g,,y+pgm n (9kabfs4km from a town that requires 50 MW of power at 12 k 9a,pq+vfmng sfygm6 k,b,(e4V. Two 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 transformer which has an 80% efficig4/sd1 i1j, t2y0moq) mdepx wency are connected tos toj/,m1ydw e 4)qdm0 pigx12 110-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 lines eacht9k ;l /ilovo6 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+l6s1wtnnt*td8uv-b4)a kx o58 m cv m 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 in transmission lines, 3ze,, 6ir*87ak ys-in cn;nwir (b ksv$R_L$ 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+zb cq+v7vb2 cchr8m , radius of 5.0 cm, and a resistance of $\mathrm{12~Ω}$ surrounds a solenoid with $230\mathrm{~turns/cm}$ and a radius of 4.5 cm; see (Fig. Below). The current in the solenoid changes at a constant rate from 0 to 2.0 A in 0.10 s. Calculate the magnitude and direction of the induced current in the coil.
I =    $ \times10^{-2 }\;A$
 ----待选择----left to rightright to left 

  A certain electronic device needs to be protected against sudden surges in cuch+goz-;83 hec n/wuqu.1b7/ tlcu ubrrent. In particular, after the power is turned on the current should rise no /7bgucu 1n.ub;u+hleo/c-h w3cz8q t 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 betw 5m)3jowkg,:m9f k* w/ c4ppeojyzh 5reen 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 T/s) must the field produced by the magnet change if the emf is to be e5jg9ropkwcy* z)43wp5k/:,mfom hj 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simple gener-jkgw2r*cs co. bz0 + ec6tmcr6j ,h-zator whose square armature windings are 6.60 cm on a side; the armature contains 155 loops and rotates in a field of 0.200 T at a rate zzj.06kc bw2 *+tjc m,es-r6c-crho g of 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for electric and magnetic fields attained in laborzwy7i0p; 3ee6xf z yt.atories areze 0eytx7zyw fi.3p;6 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 prima9r;,qydqlm n 8ry of a transformer whose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assum; dy9qq 8rln,me no current in the secondary.    H

  A 130-mH coil whose resistanb3c9 nwsw: mq8ce 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 tona (j4;t.p2; ddsljyl a 36-V battery. When connected to l 2 d;tan(ydjl;4s.jp a 60-Hz 120-V (rms) source, the current drawn is 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 wi 2pd3del/ ao1ri/z,u pth $2.0-\Omega$ 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 ca5he i cdl5at)xf5td0b2 6-ueen be defined as the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonancufeal-xd2h5eie50d 65 tc) t be. 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$