What would be the advantage, in Faraday’s experiments (Fig. Below), of usinghlap 7k ankgh.kw16 2* coils with many t2*g wap.6lka1 7kh nhkurns?

What is the difference between magnetic flux and h1y 9zwtf-ot 3magnetic field?

Suppose you are holding a circular ring of wire and suddenly thrus4m0s 4l7loxe9)e4wc oql zq )vt 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 le 9qox7s))z4m oql wc4e0vl4held 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 wirert uu.85dp 7 )auhq*un carryinp* u) t8aq. du7uu5rhng 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 thro /cjc+hl, c68fr: woysva48/eh(iin rugh the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected to the front loop, establ y6 svilr4/jccw8r(h:8ae f/,c nh io+ishing 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 directf pif03.rg m:q)d 0j ypajpw*4ion 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 “shim2;ye a6sn vu/cg o6d)elded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return current. Why is a “shield” necessary6u d2av gy6me/;)cosn ?

What is the advantage of p.s j f /8hfqxbp:ee9v0ux5 :mslacing the two insulated electric wires carrying ac close together or even twisted xx p0 5.vufqb :hm/sjfes9e 8:about each other?

Explain why, exactly, the lights may dim briefly when a refrigerator motor618zt vg.ctsbi3 2kdg starts up. When an electric heater iczgt vgbdk 8s2.1it 63s turned on, the lights may stay dimmed as long as the heater is on. Explain the difference.

Use (Fig. Below a) and (Fig. Be c0e7ji9+/qd*f fan zclow b) plus the right-hand rules to show why the counter torque iafj f c/+*eic0z qn79dn a generator opposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper or aluminum wheel2h4; ufumb:oa , or must the wheel be ferromagnetic? Explaohf umb:;u4 2ain.

It has been proposed that eddy currents be used to help sort solid waste *jm 6zevjegr(jmci.)y/ 5 -jv for recycling. The waste is first ground into tiny pieces and iron removed with a dc magnet. The waste then is allowed to slide down an incline over permanent magnets. How will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmetallic mm6my )rvvc/gejzj j e5-(i.* jaterials?

The pivoted metal bar with slots in (Fig. Below) falls much more qui1(ypeck xs0, ,1ij h5f0p jsvsckly through a magnetic field than do,(s11sjvek0, jsxip cy f05phes a solid bar. Explain.

If an aluminum sheet is held between the poles of a large bar maga sqt4 -p4hhs/d rm dv2(5ah3wnet, it requires some force to pull it out of the magnetic field even though the sheep5vh(s3ahqdsw-m h4a24/ dtr t is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a vertical metal tube reachee4xarth )j57 ms a terminal velocity even if the tube is evacuated so that there is no air reh57)r axmet4jsistance. Explain.

A metal bar, pivoted at one end, os+d 4geg 5zffo,cillates freely in the absence of a magnetic fief,e zfg+4go5 dld; but in a magnetic field, its oscillations are quickly damped out. Explain. (This magnetic damping is used in a number of practical devices.)

An enclosed transforme /i gtxy)3z(nngl;xa3r4.s hm6 /mmgyr has four wire leads coming from it. How could you determine the ratio of turns on the two coils without taking the transf/mgm lg3mix/ xgar;(4.3nn)z6sy hy tormer apart? How would you know which wires paired with which?

The use of higher-voltaqed+jizv5d-*kg79lnz j bn:9 1v8 g uyge lines in homes — say, 600 V or 1200 V — would reduce energy waste. Why are they not usedl+ubj n gniz d-k5 yjg9*vz8: 197qdve?

A transformer designed for a 12b1 vohmcy) 4qb0(os5/noei6t :ra ju. 0-V ac input will often “burn out” if connected to a 120-V dc source. Explain. [Hint: The resistance of the primary coil is usually very livrcutjo(s b)h 0o/16yema5n : oq4. bow.]

How would you arrange two flat circul;/nk dc0kt cch). 3sxxar coils so that their mutual inductance was dx)c0tkhc3nks .c;/ x
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery1q-nveepc7* wx 1c 7rw in (Fig. Below) affect the time needed for the LR circ rcn*77v qc1ewxwp-1 euit to reach
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can the rms voltage across hsiv x 0bgb0oi 9ye(5;7 (dgpi
(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 s7 ml2xqk3 d;pbource 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 impedancega;;r b*m.ywh1epmm 0 in an LRC circuit a minimum.

  The magnetic flux through 8wgsla 5cp;z,a coil of wire containing two loops changes from -50Wb to +38s 8zgpwl,5 c;a Wb in 0.42 s. What is the emf induced in the coil?    V

  The rectangular loop shown s5*r*5cw9l z sxzx -zrin (Fig. Below) is pushed into the magnetic field which points inward. In what direction is the inducex -5 *zzz9s*5srrxclw d current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being inserted into the f fphe x;q*az cb;/)c3coil. In which direction is tbz3fp)ha f*/ ec;q cx;he 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 1.10-ld3ij kum -g.1T magnetic field. The loop is removed from the field inuk1. -jdli mg3 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire is 2ljew 0-v)3 mp*sur tqinitially oriented perpendicular to a 1.5-T magnetic field. The loop is rotater t-sj vu3w l20m*)pqed 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 orient4bzq 7hazl u(l,u m(8ke)ekg.)39oova h;a il ed so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.15 s,h9zmbeauokl) l ;aevq 4izhgk),7 (l8.a u(o 3 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 o*h1nnv.m v: aof wire 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. Bemmyemvf3s0/ ..qekej 4w0kx t;s1ww ,low) is slowly increased, what is the direction of the current induced inqmke/.e,0.;mef3ytx jskwvm w4 s01 w 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 thbsv 65 )tt v;i5ajxn,we induced current in the circular loop due to the current tb;xtj5)65,svwi a nv shown in each part of (Fig. Below)?
a  ----待选择----counterclockwiseclockwise0 
b  ----待选择----counterclockwiseclockwise0 
c  ----待选择----counterclockwiseclockwise0 
d  ----待选择----counterclockwiseclockwise0 

  If the solenoid in (Fig. Below) is being pulled ar/ mvhq+ .z4uygftj z(q xc*.(way from the loop shown, in what directiof(mz4z*c/hq(yxutj r+q .v g.n is the induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field p ,ggl0q+g qu+jerpendicular to a circular wire loop 12.0 cm in diameter is changed from +0.52T to -0.45 T in 180 ms, where means the fieguqg0+ jl+ g,qld 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 (Fi6at:lx.1ti v*+mh 36dlct behg. Below) is 12.0 cm long and is pulled at a speed of 15.0cm/s If the magnetic field is 0.800 T, calcu :xacl3hi*6e m1vbt6lt th+d.late
(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 lies7t-)q i p kdt,kg1f8tk in a 0.75-T magnetic field pointing into the paper. If the loop’s diameter changes from 20.0 cmpg) ttkidkqft8 ,k 1-7 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 lonyjj m1k.: x4eui i :7p6xhilu4gr7( xsg and generates an emf of 120 mV while moving in a 0.90-T magnetic fiex6 y spxjrih1uxe7ij 4i .g( :4ukm:7lld.
(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 01+lxka6qhbt (Fig. Below) abl6tx1+qkh0 is situated inside a region of uniform magnetic field of 0.550 T. The total resistance of the loop is $\mathrm{0.230~Ω}$ Calculate the force required to pull the loop from the field (to the right) at a constant velocity of 3.40m/s Neglect gravity.    N

  A 500-turn solenoid, 25 cm long, p, .q4s9kep;olfwr 9 qhas 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 during thiqkr9we9ppq;f4,lo s.s time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves with a speed of 1.6m/s is 30.0 cm 7 g1i gnb7b74u spbswo:fo(i1long, and has a pbu b1b7g 7n(ogsfwi:os1 7 4iresistance 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 turn0qu za+ w pog- i/4g.jtdg1g:yt)tji (s of circular copper wire 2.6 mm in diameter. A uniform magnetic field,uo0+ tjp:gg(gt)aqd4yz j-. i tg 1/wi 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 to a single 13.2-cm-diameter circular yx90ih8 .qv nt9spsst)ul qpz7,4ww: loop of copper wire decreases uniformly from 0.750 T to ze79 su40 qizxwp )svly ,hwn.stp:89tqro. 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 genera .5id7)-tratks hpp 6n.9ejkp te a peak output voltage of 24.0 V. The square armature consists of windings that are 6.0 cm on a side and rotates in a7th) .rs5k9eink t pp-jd6p.a field of 0.420 T at a rate of 60.0rev/s How many loops of wire should be wound on the square armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 11)ss nvmlqd*bw-11 j ;j00 rpm produces 12.4 V. What will the ou tput be at a rotations*dl q;v)1n1wsb -jjm speed of 2500 rpm, assuming nothing else changes?    V

Show that the rms out49)ks qowy8 hbput (Section 18–7) of an ac generator is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 320-loop square coil 21.0 cm on a side. How f a. 0* z8sb6w3bfxzcngast must it turn in a 0.650-T field to produce a 120-V6w z8gfc*b3 xn.bz0sa peak output? $f$   rev/s

  A 450-loop circular armature coil with a diameter of 8.0 cm rotam6ig6*f 8;gh n lr5anc57rdg ttes at 120rev/s in a unifa chnti76mdrgn5 gl*r5f; g8 6orm 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 field of 0.030 T. It has 1000 ts-asx htmo: /3g1om *purns and produces an rms voltage of 150 V g1 s x :/t*o3mpasomh-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 resistance of pdnim-- 1dpvw3yl3 v- zdd,+b$3.25\Omega.$ 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 opeqyfgt ,e7aqvv7;mw: 3 rating at 1800 rpm. What would be the back emff3q:t ;aqv w myev,g77 at 2500 rpm if the magnetic field is unchanged?    V

  The back emf in a motor is 95 V when the motor is o(.w bu/)hmwaz perating at 1000 rpm. How would you change the motor’s magnetic field if you wanted to reduce th.hab/mu z()ww e 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,urbrz st3 :sa.-9g mn it to run at half srnsubrmg. tz-9 a :s,3peed?    A

  A transformer is designed to change 120 V into+hd;z k: pcrh;/wh p/x 10,000 V, and there are 164 turns in the primard/xck hrh p ;w;z/:p+hy coil. How many turns are in the secondary coil? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 V. What is the currentn, yf22ucz d(.g/fat h in the secondary coil as compared to the primar,.z gtdu2chn a2f y(/fy coil?   

  Neon signs require 12 kV for their operation. To operate from a 240-V line, whq2lry, o ri74mat must be the ratio of secondary tlyr,72miq4 roo primary turns of the transformer? What would the voltage output be if the transformer were connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer plugs into 120-V ac and draws 0.35 A while supplyide/0pv chu- z5ng 7.5 A tp/zc0d eu 5hv-o 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 transformer is 12 V, acy6r:*ff b-fy nd the input current is 22 A.6yfc*: yfr-fb
(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 priey-ohau 6 * 9m+uj1qppmary turns and 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A. What are the output voltage and input ceqj1*p+yu o- muh6pa9 urrent? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =    V
$\frac{I_\mathrm{s}}{I_\mathrm{p}}$ =    A

  If 30 MW of power at 45 kV (rms) arri x83k+bq8kfxives 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 ov)zjm;eq46p7; eu5kpc7 x jac- bf.yzter two $0.100-\Omega$ lines. Estimate how much power is saved if the voltage is stepped up from 120 V to 1200 V and then down again, rather than simply transmitting at 120 V. Assume the transformers are each 99% efficient.    kW

  If the current in a 180-mH coil changes steadily from 25.0 A to 10.0 Ao.u;,of7 smg +nry8fx in 350 ms, what is the magnitudeyxn r+f, ;8.7 mgsofou of the induced emf?    V

  What is the inductance of a coil if the cok.k0 *wypwor. v1a,unil produces an emf of 2.50 V when the current in it changes from -28.0mA to +31.0mA in 12.ww au. *.1vny ropk,k00 ms?    H

  What is the inductance L of a 0.6ui,53qcwtcr:;sta, t vdq +,r0-m-long air-filled coil 2.9 cm in diameter containrdt:3cq5wrs+tq ,t,v,a u ci; ing 10,000 loops?    H

  How many turns of wire would be required to makyvxspi3aso()hpffk*8)ama : e , +z2c e a 130-mH inductance out of a 30.0-cm-long air-filled coil with a2pkf,) *a(fsp xcz3myvho) es a+8a i: diameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor3s:f(o22aojjx0guv n has 2800 turns, and it is 2.5 cm in diameter and 28.2 cm ogfa2v0ox u2 3j:( jsnlong.
(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* a lf+ ,y3e 388oh:ofldyedxlnd 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 wound solenoid is unwound and used to make anotherzzq wo u; rx/ )r:2i)i;t/xk. 9cnfkrm tightly wound solenzfq 2 zi:x/uckrw;r r)n/)i k;9xmto.oid of twice the diameter. By what factor does the inductance change?   

  The magnetic field insifoe 65s pn4zn j+y-8xkde an air-filled solenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how much energy is stored in this fien+-sf56 jn z8pxyok 4eld?    J

  At a given instant the current t0o b -1p3veuau, .knwohrough 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 known to be 60.0 mH, and how lon. p1vanb -ue3u0 o,wkog 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 magne v t0nm7(mcp/0mgdc1qtic 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 current in (f7w):a6 9foq.ss j itfFig. 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-sectionalgi q b8(e*0udv area. But solenoid 1 uses wire thv* (d bq0u8eigat is half as thick as solenoid 2.
(a) What is the ratio of their inductances? $\frac{L_1}{L_2}$ =   
(b) What is the ratio of their inductive time constants (assuming no other resistance in the circuits)? $\frac{\tau_1}{\tau_2}$ =   

  What is the reactance of a-xbze1c 3nz9v-)jcf nex ln3+ $7.20-\mu F$ capacitor at a frequency of
(a) 60.0 Hz,    $\Omega$
(b) 1.00 MHz?    $ \times10^{ -2}\;\Omega$

  At what frequency will a 223uc7w5tsn- w( k x:fsp.0-mH inductor have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency wi+mxgp4fmkq m vq0 d;,3ll a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactao-y-5hg5mapov-ezdi 74p25 r vzn1p unce of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of a 1.0-mH inductor as a functi ,x3v/,pis-xr 2m fpxgwe:3(/ pappjion of frequency from 100 to 10,000e:pg2i(iv- spmjpp33w//, rfxp ax, x Hz.

  Calculate the reactance of, and rms curre3 (.lbbn- *bka.g/ w bsvpdl6g gad7n.nt in, a 160-mH radio coil connected to *n.7/.da dg(pbg6kv .3 lsbnb-baglw a 240-V (rms) 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 draws 12.8 A. What9oz:/wcx g(dk99 dsy tgf -nv1tnd0hn3 b(6pu is the coil’s inductazcgvudnn y0w:d -9o(xd6h k 3nbt p9f9/t1s(gnce? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a well-insul9lqmir jyr. jhs)b0s fc - ys*c3nep(p.f2t1; ated $0.030-\mu F$ 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 ulhoy *b,a 0+ 2+konwu0j8lt pcurrent of 70 mA passing through the human body for 1.0 s could be lethal. What must be t0yo,ou w u8 lh+jl+bna0*tkp2he impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if itbo rn6-t 7:ls ,vb pb st,;8fw3ql8xpjs impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms current in an Lco2os3t.j d-p5 gg2 xdRC circuit connected to a 10.0-kHz, 725-V (rmg3c -d5po2sxotd g.j 2s) 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;7rh2 g vtkpn3d .wdx h(pm05c driven by an ac power supply. At what frequency is the impedance double that o3kg7 d;p0p.d5h v xchnwrt 2m(f the impedance at 60 Hz?    Hz

  (a) What is the rms current i;zt*) jg5au4-z- cohn4 oymbh n an RL circuit when a 60.0-Hz 120-V rms ac voltage is applied, )tnboc-hm- az*4;z u 4 hy5ogjwhere $R=1.80\mathrm{~k}\Omega,$ 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 circuit if9 p6ci ;b5cwn wvqbt 3nf+lkx0up-/9x $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ 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 8mwz 1 h*xpp*nconnected 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 capacita./fzc aklxr q3y qk 2hjc.(8s0nce of 2800 pF when the radio is tuned to. j83kcly0x /arfz(2.qcq shk 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 = 1+0ja-zlnx*k: qed 5 fz4.8 mH and $R=4.40\Omega$.
(a) What value must C have to produce resonance at 3600 Hz?    $ \times10^{ -7}\;F$
(b) What will be the maximum current at resonance if the peak external voltage is 150 V?    A

  Suppose you are looking at two current loo8dx6bq .o qk ,2yf2srwkoc:8gsuo3p, ur 81sqps in the plane of the page as shown in (Fig. B, dbpscsyuq x862o.gosk8rr o 1, wk:fu3q82q elow). 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 side h+dq)d7jk9m nb as 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 onq*u;ay qt sz ,dm,6d,wly 12 V. It contains ad6zm q* audwt; qs,,,y transformer that converts 120-V household voltage.
(a) Is the transformer step-up or step-down? this is a  ----待选择----step-downstep-up  transformer
(b) What is the current in the secondary coil when the lamp is on?    A
(c) What is the current in the primary coil?    A
(d) What is the resistance of the bulb when on?    $\Omega$

  Power is generated at 24 kV at a generating plant located 118 km fromk*4k:3hdd muwb,uw ;p* f bjy7 a town that requires 50 MW of power at 12 kV. Two transmission lines from the plantmu,7 ;wbfhy k *dw3udbp: k4j* 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% efficiency are7ckmw8 wnny8e8yvt ,0 connected to 110-V ac. The secondary windings are co7,cv8n mtwkn y0w8y e8nnected across a $2.4-\Omega$ 75-W lightbulb.
(a) Calculate the current through the primary windings of the transformer. $P_S$ $\approx$   A
(b) Calculate the ratio of the number of primary windings of the transformer to the number of secondary windings of the transformer. $\frac{N_\mathrm{p}}{N_\mathrm{s}}$   

  A pair of power transmission lines each hawp*3t6vbb 3v v(auk kjsxw22 u7 ,3hbqve a $0.80-\Omega$ resistance and carry 740 A over 9.0 km. If the rms input voltage is 42 kV, calculate
(a) the voltage at the other end, $\approx$    kV
(b) the power input, $\approx$    $ \times10^{7 }\;W$
(c) power loss in the lines, $\approx$   $ \times10^{5 }\;$W
(d) the power output. $P_{out}$ $\approx$    $ \times10^{7 }\;W$

  Two resistanceless rails rest 32 cm apan hq;kx oqr) v)8+di g,pzl/1crt 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 -ahv7t0h 8hkm z v/xdi-v e*t+loss 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, and a resjc ze0m czxd 21.no1s/istance 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 su1 hr 3rnan8 bh0u.:f(n1hbxjlrges in current. In particular, after the powear .f1r nhub3x( hl8n0b h1:njr 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 betg6jj.d8sf7p7qp-k fl ween 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 chjf.g7ldj8 -p7pk6qs fange if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simple generator whose square armature wic tj;339orkpn hcknw*l3z 6)q ndings are 6.60 cm on a side; the armature contains 155 loops and nk; qt9z33 ch)rpo3lk6ncwj*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 9jznh.;wtyo ii v n661bm/k(n attained in laboratories are abo /.(my;96kntiwh6nno j z bvi1ut $1.0\times10^4\mathrm{~V/m}$ 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 whodmn e5sec1vve28yf n,u-i m25 se input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no current icevmd2, sm-5 n15fein2 yv 8uen the secondary.    H

  A 130-mH coil whose resi -zag-d,,f0fupb mad 7stance 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 whlvwt7uvr*d l o4 *t7lh+mu5u1en 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 and resistance of thet m7lhd1 o4v+uu5* rlutl *wv7 coil.
$V_{dc}$ $\approx$    $\Omega$
L $\approx$   $ \times10^{-2 }\;H$

  A 135-mH inductor wit yguyf (:r/:xxf0.b-y 5oqslhh $2.0-\Omega$ resistance is connected in series to a $20-\mu\mathrm{F}$ capacitor and a 60-Hz, 45-V source. Calculate
(a) the rms current, $I_{rms}$ =    A
(b) the phase angle. $\phi$ =    $^{\circ}\,$

  The Q factor of a resonance circuit can be defined ju1hrg *s su9*:h+qqgg5jnd5ad i8a1as the ratio of the voltage across the capacitor (or inductor) to the voltag dhq+s 1ig h*5:jg ajqarn 1dsg5u9u8*e across 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$