What would be the advantage, in Farada m v9xozf+ 9:o -ps0oc5iph1 -i/stbxoy2rj4py’s experiments (Fig. Below), of using coils with many turotisoz2yjc0ri9h -m o+9s5xp1 xpob4p/-vf: ns?

What is the difference between magnetic flux aw*5 6m:wu:joyqa ve2b(ka c2ond magnetic field?

Suppose you are holding a circular ring of wire and suddenly thrusrdtl+8yy;s(+ 3dpj,et yt hz/ t 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 the ring? Is a current induced when you withdraw the magnet? In ea tyh; t3d8(yp+,ysl/r+jdzetch case, if your answer is yes, specify the direction.

Two loops of wire are moving in the vicinity of a very long straight wire carc 6.;jqjv7v furying .cvf ujjv7;q 6a steady current as shown in (Fig. Below). Find the direction of the induced current in each loop.

Suppose you are looking along a line tuj9 5 vcyf2.;j5wja cne2fn p(hrough the centers of two circular (but separate) wire loops, one behind the other. A batteryyen2c (w2nj 5.fcfp ;j95ajvu 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 curren zv0xnme7by;6ln:d x;t 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 signa4s)hvoy )*bl il must travel over a distance, a “shielded cable” is used in which the signal wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return current. Why i*i hvs)4ly)ob s a “shield” necessary?

What is the advantage of placing tk;dp9w*pzck5- l iu8xhe two insulated electric wires carrying ac close tog iu;xpk5d9kz -8cwl* pether or even twisted about each other?

Explain why, exactly, ( beh)+e)g/v mywkr* sthe lights may dim briefly when a refrigerator motor starts up. When an electric heater is turn*b r(+v gh)ye/emwsk)ed 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 theea*vg me2o ,v( right-hand rules to show why the counter torqu m gev2o(,vae*e in a generator opposes the motion.
a
b

Will an eddy current br8g*kbu7as * thake (Fig. Below) work on a copper or aluminum wheel, or must the wheel8g*tha7*buk s be ferromagnetic? Explain.

It has been proposed that eddy icve4iofx 9m(r;3 zyz;4c1 r tcurrents 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. Htz4;cx ;iz1om4 9 r ervif(cy3ow will this aid in the separation of nonferrous metals (Al, Cu, Pb, brass) from nonmetallic materials?

The pivoted metal bar with slots in (Fig. Below) falls much more quzh szxeo4 *,,gickly through a magnetic field than does a x4sz h,e*z,go solid bar. Explain.

If an aluminum sheet is held between:fyvd7my yu v8agbb;l7do*/hv1 4hp3 the poles of a large bar magnet, it requires some force to pull it out of the magnetic field even though the sheet is not febo7* 8ypl yvba7v/4:mdudhf h;ygv1 3rromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a verticsbm bi:,t;73 et nf3zjal metal tube reaches a terminal velocity even if the tube i itejs,z3 ;bmfn:t7b3s evacuated so that there is no air resistance. Explain.

A metal bar, pivoted at one end, oscillates fr-efe apcocyzh 7zx p49 c+5tj *w1.l.peely in the absence of a magnetic field; but in a magnetic field, its osc 5 c7o-yt4whe*e.pc1cxa.zzpl +pfj9 illations 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 detb lft4qnyf);-ermine the ratio of turns on the two coils without taking the transformer ap)-y q4;flbnftart? How would you know which wires paired with which?

The use of higher-voltage lines in homes — say, 600 V or 1200 V — wou1 ypg )cjx2) n*lu7bkrld reduce energy j )x*lyur)c gbpk72n1waste. Why are they not used?

A transformer designed for a 120-V ac input will often “burn out” if connec;b 17f .pv mwr 9rqqmg7-e-ryhted to a 120-V dc source. Explain. [Hint: The resistance of the primary coil is usually ve. -wfrvq9mm ;7req1y-bhg p7 rry low.]

How would you arrange two flat circular coils so that their mp-yw7 af*;xpp utual inductance waswxp a *-pf;p7y
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Below) affect the time needtye 1vgt,1x,pmb/4 i zed for the LR circuit to reachxtyvgze 1 bp t,i/1m,4
(a) a given fraction of its maximum possible current,
(b) a given value of current? Explain.

  In an LRC circuit, can th* g:zdd, gf)dne rms voltage across
(a) an inductor, ----待选择----yesno 
(b) a capacitor, be greater than the rms voltage of the ac source? Explain. ----待选择----yesno 

Describe briefly how the frequency of the source emf affects thx (zo8udfgzj 6v5i2)je 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 -(ti+f 7 )6;fh7 wyze tfxo vyu2ms8hnLRC circuit a minimum.

  The magnetic flux through a coil of wire contauw-/lt1dq3o wszb25e ining two loops changes from -50Wb to +38 Wb in 0.42 s. What is the emf ind/wz1e3 w2d tbl5q os-uuced in the coil?    V

  The rectangular loop shown in (Fig. Below) is pushed into the mag llm/sde9(2go+ bnjq/ netic field which points inward. In what direction inmb2sljoe/+/9q(ldg s the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being inserted into t/v r6w b n gmg/up+9g(/c:cquphe coil. In which direction is the inducep(9/bc// rgnvgwgu+ 6cqp: mu d current flowing through the resistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wi*g)acdhgg6 o 5re is in a 1.10-T magnetic field. The loop is removed from the field in 0.15 s. What is tg )*g ocdhag65he average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire)0jnl ha*ft 1 ecsfl-: is initially oriented 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 the average induced emfh*:- a0l sc1n tfe)fjl in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially oriented s7ergxfym4(:z,h 5dj-m 3 t nm cwf8sf(o that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.15 s, the fiel3-zghf( (,rds cmf7: njxmy m4fw58et d 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 in v-dbyc b4m3h4 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.s:dlb5 w,i3w m04xka0 ,y;y,u htywhh Below) is slowly increased, what is the direction of the current induced in the small circular loop inside y3ash,ul bhmt5 0wk,4,hxwywidy0;:the larger loop?  ----待选择----counterclockwiseclockwise 
(b) What would it be if the small loop were placed outside the larger one, to the left?  ----待选择----counterclockwiseclockwise 

  What is the direction of the induced current in the circ )kijc)1uzn7dvopg4/hf bq y 78+osj8ular loop due to the current showy1njfod)u887/4v kh z s 7qopjgi)cb+ n 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 beingw ,yc4hr3 )yv 4pohuoq)e w8.j pulled away from the loop shown, in what directionhvqo o8.4)3hyy,weujprcw 4) is the induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to;kh (9w; ugy2yb hzaqbwk4r18 a circular wire loop 12.0 cm in diameter is changed z(1hqwk bhwr 8 a;;yk2u49gybfrom +0.52T 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.g 6x/mulmy1 q5 Below) is 12.0 cm long and is pulled at a speed of 15.0cm/s If the m yq6ug m/x5lm1agnetic 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 the plane of the paper lies in a 0.75-b9ye(u(tal ,tT magnetic field pointing into the paper. If the loop’s diameter changes from 2y et,u(t la(9b0.0 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 c:ec),1janh nbm long and generates an emf of 120 mV while moving in ebn1) hn,j:aca 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 ( a6.usoob0/ ozFig. Below) u.ooo6 ab/0szis 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, has a diameter of 2.5 csxoxmsp.e .dm9tp t-b7y eb l-- 4-h(cm. A 10-turn coil is wound tigh9-loxs. d p-7c4tse - .yhmbetpb -x(mtly 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 this time?    $ \times10^{-4 }\;V$

  In (Fig. Below), the rod moves with a speed of 1.6m/s is 30.0 cm long, and has pft- 4v j.llacu;/s6ia resista fll aj4t-pv.6icu;/snce 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 cor-x5bk ;ry 3)qxz kwg0nsists of 20 turns of circular copper wire 2.6 mm in diameter. A uniform magnetic fi3x5 qzk x;0b )ywk-rgreld, 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-dider(:ebhmc:9 p 4 j od(zfke/4ameter circular loop of copper wire decreases uniformly c eob e:/e 9dm4jh(z4p:(kdfrfrom 0.750 T to zero. 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 outpu;(u (g-se6.hkv kncjh(cg.,d c vsp+xt voltage 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 should be wound on the square scg(.-ve, cu; p+ vd(xh. 6(cgskhjnk armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 1100 rpm produces 12.4 V. What a3my)h ) rrv7gwill the ou tput be at a rotation speed of 2500 rpm, assuming nothing else change7m3hrygv)) ar s?    V

Show that the rms output (Section 18–7) of an ac generator )r;mnsl17r0 ,ug 3nlsrfo,3htw8 ov r is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 3ova.rw0rp m7.20-loop square coil 21.0 cm on a side. How fast must it turn in a 0.67 po .mrr.w0av50-T field to produce a 120-V peak output? $f$   rev/s

  A 450-loop circular armature coe6g., 4p-pk kxnq vhp3il with a diameter of 8.0 cm rotates at 120rev/s in a - qk3pkphp e6x.4nv,g uniform magnetic field of strength 0.55 T.
(a) What is the rms voltage output of the generator? $\approx$    V (Round to the nearest integer)
(b) What would you do to the rotation frequency in order to double the rms voltage output?  ----待选择----oncedoubletriple  the rotation frequency

  A generator rotates at 85 Hz in a magnetic field of 0.030 T. It fm*bjwyms; cy hq8t8.y 8n+y2has 1000 turns and produces an rms voltage of 150 V andsc;+8w yj2hmfy* ymbny 8 qt.8 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 resistnqe/9th5urm i 1e 1uscp;zp85ance 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 opercv9r 2,i: dvsl2y bao;ating at 1800 rpm. What would be the back emf at 2500 rpm if the magnetic a yrv2vsic,;ob9l d2:field is unchanged?    V

  The back emf in a motor is 95 V wh + xfc+mzzllmt+cg. (nxy.i4. en the motor is operating at 1000 rpm. How would you change the motor’s magnetic field if you wanted to rexnt xl mmcz cf++lz+. 4.g.y(iduce 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–uq-:kzz jy45k 9 if the load causes it to runqjk4zu :ykz-5 at half speed?    A

  A transformer is designed to change 120 V into 10,nk6p4abvdpd7 :,ay f) tco8)y000 V, and there are 164 turns in the primary coil. How many turns are in the secondary coil? :d6v4 7tf o8, p)aabyyp )kdcn $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 V. What is the current in t;3cbohh8 lqz;mlq- .ehe secondary coil as-l ; hhqoqe8z3; lmbc. compared to the primary coil?   

  Neon signs require 12 kV for their operation. Toohbvrp ne9 xh/xa7;8 e*5i+s s operate from a 240-V line, what must be the ratio of secondary to primary turns of the transformer? What would the voltage output be if the transformer were con8x oe;97h* sn5rh/xsv e abi+pnected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transformer p 2f, g-fakze1klugs into 120-V ac and draws 0.35 A while supplying 7.5 A to the traine-za,2fg1k fk .
(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 curr lg t4ck.r-om/ent is 22 A. 4.r-tml /cgk o
(a) Is this a step-up or a step-down transformer? this is a  ----待选择----step-downstep-up  transformer
(b) By what factor is the voltage multiplied? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ =   

  A transformer has 330 primary turns and 1340 secondary turns. The input vol:yp( fbdi 3auhow (.7iq2q3 zktage is 120 V and the output current is3 d7 yq3ob h:2if(qp kaw(.ziu 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 kV2oe4 pjpz: ;gw (rms) arrives at a town from a generator via $\mathrm{4.0-Ω}$ transmission lines, calculate
(a) the emf at the generator end of the lines, $\varepsilon$    V
(b) the fraction of the power generated that is wasted in the lines. fraction wasted   

  65 kW is to arrive at a town ovh8 nky7h;0 bcyp m/yf0er 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 A iw8v +0 )27xda uzsfie(rd)rjvn 350 ms, what is the magnitude of the induj0efrr+ ) d27z(8xsw)viv aduced emf?    V

  What is the inductance of a coil if the coil produces an l(tx8 .//c8dhg2qqd8hik qp n emf of 2.50 V when the current in it changes qihtl.8 d2 /gdk8qqn/(pcx8h from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of a 0.60-mavbdce. /,9y m-long air-filled coil 2.9 cm in diameter containing 10ed,cv aym /b.9,000 loops?    H

  How many turns of wire would be required to make a 130-mH 5 e.8ja1a+dbo4b x3 3hqwblzf inductance out of a 30.0-cm-long air-filled coil with a diameter of 5.2 cm? L35 3l8wbab.eh41qx +zdojfba$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and it is 2.5 cm in diam2) in dhvdoftfs+5 q6oy10fu: eter and 28.2 cm long:5fn0y ufsotdd6o 1q f) hi+v2.
(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-se(ug5atmf9m,o m-m.nn ; :8 stoi*fjimctional 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 tmjk+aeggtl .h2(l )ek+ vn )(jo make another tightly wound solenoid g h).lge+ k( je)2+ntlkaj(vm of twice the diameter. By what factor does the inductance change?   

  The magnetic field inside an air-filled so ,lsmu vptx kc;.d0.zf8y )t1+pp ins+lenoid 36 cm long and 2.0 cm in diameter is 0.80 T. Approximately how much energy is stored in thiss cy01 ktlm;i .+nf s,xzut. 8dp+)ppv field?    J

  At a given instant the current through an inductor is 50.0 mA and is incr-o,g-qq9,hcjqbq :rk m7w9hh easing at the rate of 115mA/s. What is the initial energy stored in the inductor if the inductance is known to be rc whqqh9g,-q-mb,9:h okjq7 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 abo+ 4 cxxy2.ln;ulc6mlgut $0.50\times10^{-4}\mathrm{~T}$ 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 ighb:0 d6fr.xp4h (c rconstants does 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 al6iff/ 4.l8ra(.jm+ lwnhagpnd circular cross-sectional area. 6 +w lahnr/mpffa(.4 ji8g.llBut solenoid 1 uses wire that is half as thick as solenoid 2.
(a) What is the ratio of their inductances? $\frac{L_1}{L_2}$ =   
(b) What is the ratio of their inductive time constants (assuming no other resistance in the circuits)? $\frac{\tau_1}{\tau_2}$ =   

  What is the reactanceuz rs3g i8abaha2s/( ; of a $7.20-\mu F$ capacitor at a frequency of
(a) 60.0 Hz,    $\Omega$
(b) 1.00 MHz?    $ \times10^{ -2}\;\Omega$

  At what frequency will a 22.0-mH inductor have a reactancx. uf669);la gitbr )t xgqxg(e of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency wijzf a;v++z9 lall a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactancep sdccjw1b8qwj0 +; 8x of a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance,fr fsane- id4 ))b 8hifxbt23l (xi5t of a 1.0-mH inductor as a function of frequency from 100 to 10,08i an)ifx-l h2e, dri(xbt 4) 5f3ftsb00 Hz.

  Calculate the reactance of, and rms current in, a 160-mH radio coil cl7x-uu ac 2(;ojbuwx/ onnected to a 240-Vuab( ;x2 - 7lwxojcu/u (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 d::q , k q8fhttk0hzjrq(f4*aqraws 12.8 A. What is the coil’s in j kqahzttfr0h4::*k8q( qq,fductance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance mwl383 rez s-ue(ypx3fc76b cof 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 pa i 0eyv)ky 2 j3t)v(8zti*vwilssing through the human body for 1.0 s could be lethal. What must be the impedance of the body for this032iytvlei z*vivtky) w)8(j to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of an,w4 0 sf3 i- fmwyv;ici8bpc+ coil if its impedance is $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms cz.pkz0uw :;g9hk/w 0-kvql5o cviz 9gurrent in an LRC circuit connected to a 10.0-kHz, 7250woz; kkw/ gq9vgk-50.zvic:hl zu9p-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-(v/ xn ya*mcsie00-ujmH inductor is driven by an ac power supply. At what frequency is the impedance double tme cn(sxji - 0uv/ay*0hat of the impedance at 60 Hz?    Hz

  (a) What is the rms current in an RL circuit when a 60.0hn8i or 1*p:qq-Hz 120-V rms ac voltage is applied,*oq:in8r hqp 1 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 c) yrzj6,zho a8oh.8o murrent in an RC circuit if $R=8.80\mathrm{k}\Omega,C=1.80\mu\mathrm{F},$ and the rms applied voltage is 120 V at 60.0 Hz?    $ \times10^{-2}\;A$
(b) What is the phase angle between voltage and current? $\phi$ =    $^{\circ}\,$
(c) What are the voltmeter readings across R and C?
$V_{rms\,R}$   V
$V_{rms\,C}$    V

  A 3500-pF capacitor is connectenu 6 6dmny/xq n2);(9 ctobaccd 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 )uayw-6)xg ue- f nlo9in the tuner of an AM radio has a capacitance of 2800 pF uw e)6u9 flgn-)a x-oywhen 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 m+fg (jmp q ctlgyb)i 54*ro,y,3kyzu,H 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 cxx9 axvea,l-w 6)z.tx, vg(x murrent loops in the plane of the page as shown in (Fig. Below). Whenxm)xa9.6 eg ,-,wx(lav x xvtz 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 resistanki2juwr- 01k gexway.c5h+-m ce 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 reqmo/*p(b* ed/s yf q7ukuires only 12 V. It contains a transformer that converts 120-V household voltage. q*pbofsk u/em7 *(/ yd
(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 qs1snk nma9ew9-ex + .km from a town that requires 50 MW of power at 12 kV. Two -e9x1mesw qa9n+ s n.ktransmission 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 hako7 4y.q0wku is an 80% efficiency are connected to 110-V ac. Thek74w. u0kqioy secondary windings are connected across a $2.4-\Omega$ 75-W lightbulb.
(a) Calculate the current through the primary windings of the transformer. $P_S$ $\approx$   A
(b) Calculate the ratio of the number of primary windings of the transformer to the number of secondary windings of the transformer. $\frac{N_\mathrm{p}}{N_\mathrm{s}}$   

  A pair of power transmission lines each have at7 yahxy3h4r0oru 6 s:hafr3* $0.80-\Omega$ 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(f5t- tp4 ;gsna19wwhx/u mdd 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 transmg yt/:atb.z7 tission 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 ag+m1i d 0sqf5a 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 b+6tv*gj/ ul uk vrqqni m75wow)2-o9be protected against sudden surges in current. In particular, after the power is turned on the currer+n qv*v5uguji7- 92q owmowl k 6/tb)nt 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-diamet5vabq3h oi :m9er coil is placed between the pole pieces of an electromagnet. When the magnet is turned on, the flux through the coil changes, inducing3m ho9a:vq5ib an emf. At what rate (in T/s) must the field produced by the magnet change if the emf is to be 120 V? $|\varepsilon|$    T/s

  Calculate the peak output voltage of a simple generatoref.c y)nkbi0 3 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 of 120rev/s. .) cikfy3be0n$\varepsilon_{peak}$ =    V

  Typical large values for electric and magnetic fields attain g7tea ;j :m;xwmy(2oned in laboratories a(x7;;emtmjgyo: 2nwa re 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 th0dl88q+o lpnb0f7j ttufov,kt*1k/xe primary of a transformer whose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume o80 o,7p 0kv*tlu8t+ jk/fxnq bdt l1fno current in the secondary.    H

  A 130-mH coil whose resistance u8e6heme/;te is $\mathrm{18.5~Ω}$ is connected to a capacitor C and a 1360-Hz source voltage. If the current and voltage are to be in phase, what value must C have?    $ \times10^{-7 }\;F$

  An inductance coil draws 2.5-A dc when connected to a 36-V batte0kb(.r84au9/b b hw.pe vk wapve(/ ndry. When connected to a 60-Hz 120-V (rms) source, t(./.knapuh a8bvv d4e ebwp09wb( k/rhe 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 wit/j+o wpfvyb;si)(i *vh $2.0-\Omega$ 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 sx91jfc.e)ve as the ratio of the voltage across) evfx1j.e9s c the capacitor (or inductor) to the voltage 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$