What would be the advantage, in Faraday’s experiments (Fi5 59lzu 6i.7k1ex+g prdwip4js)rf( hszkf:mg. Below), of using coils wit hp.km 6fgxi4sz (1lr) 5zkw5 fjrpse:9d7u i+h many turns?

What is the difference between magnj; pgsn r,e1y3etic flux and magnetic field?

Suppose you are holding a circular ring of wire and suddenly thruswhpa2g r,z 59m )hlsp0t 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 withdrlgsm)hzpha r2p95w0,aw the magnet? In each case, if your answer is yes, specify the direction.

Two loops of wire are moving in the vicinityrvq xs 2mcr4ruz /x(2* of a very long straight wire carrying a steady current as shown in (Fig. Below). Find the direction of the induced curv4rzxx2q2mu*rs /c (r rent in each loop.

Suppose you are looki);58 gdfc,s q0eft wtxng along a line through the centers of two circular (but separate) wire loops, one behind the other. A battery is suddenly connected to the froqx )stce 8,t;ffg0d5wnt 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)l7t p;rww *sgi(qpu5dg +kk: 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 m43 d.svjsi;ra distance, a “shielded cable” is used in which the signaljdm.s3;i 4rvs wire is surrounded by an insulator and then enclosed by a cylindrical conductor carrying the return current. Why is a “shield” necessary?

What is the advantage of placing the two insulated hiegc* 1vda*; 5e56kfvqg s6n electric wires carrying ac close together or even k;eh d sqgv6c6vg1 **5fne5 aitwisted about each other?

Explain why, exactly, the lights may dim briefly when a regj8 tbx3vg5 5zzwqpy 324hj5vfrigerator motor starts up. When an electric heat8zg gthbv j3wpq5 4jz325x5vyer 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 rules to show wh )/h7,(vq jd gywzaflv7+egt 7y the counter torque in a generayf7eg,(j /+qz7gwv)thva dl 7 tor opposes the motion.
a
b

Will an eddy current brake (Fig. Below) work on a copper orqhmtjdm 3 hem4 0h 533om//myv aluminum wheel, or must the wheel be ferromagnetic3emyjtmmo/3dhmhm v4/hq0 5 3? Explain.

It has been proposed that eddy currents be used to help sort solidj e(wxxj,g *i: waste for recycling. The waste ise*j:i(wx g,xj 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 materials?

The pivoted metal bar with 7*cxlax ky,t b0t ,0 fbc 1+,,ybbl:v3ylmwkaslots in (Fig. Below) falls much more quickly through a magnetic field than does a solid bar. Explainyvt0lykxbtc k7bb+,m0 c x* ,bflw3y,,a:a1l .

If an aluminum sheet is held between the potc +g:(efz(4 1ydbns oh/wmzl/o;gn 5les of a large bar magnet, it requires some force to pull it out of the magnetic field even though thenz1+ hemf gd/:cwyl(;go nt/b4 z5(os sheet is not ferromagnetic and does not touch the pole faces. Explain.

A bar magnet falling inside a vertical metarfqk2/ (8rb3 8awxuq.aa0 uoypj3 9 ryl tube reaches a terminal velocity even if the tube is evacuated so that there is no air resista(8r y yauu/x f8wb.r3 03rqoakp9aq2jnce. Explain.

A metal bar, pivotedn8 cq7 u4dx8xg:8cl kc at one end, oscillates freely in the absence of a magnetic field; but in a magnetic field, its oscillations are quickly damped out. Explain. 48 cx nlq8:dug8 ccx7k(This magnetic damping is used in a number of practical devices.)

An enclosed transformer has four wire leads coming from it. Ho):p2fdqt i 6oimrpn,0w could you determine the ratio of turns on the two coils without taking the transformer apart? How would you know which wirespqp0:r dnf o 2ti)m6,i paired with which?

The use of higher-voltzgty6. mgg)cvc dz;zed 1o/9ot c*wf +7h7u 0jage lines in homes — say, 600 V or 1200 V — would reduce energy waste. Why are the7mtfdduc/t1+0ogwzzgcg76h)ev jc y;9z*. o y not used?

A transformer designed for a 120-V ac input will often “burn out” if c2)rx81 w*cye dlxcbl0 e3; aivonnected to a 120-V dc source. Explain.xrd ei2cc1)l0e; 3 v*w8la byx [Hint: The resistance of the primary coil is usually very low.]

How would you arrange two flat circular coils so that thd;n58v+ipk *kjhc2zpj8+iy leir mutual inductance waskkl 5pj8d hcv82+z n*pi;yij+
(a) greatest,
(b) least (without separating them by a great distance)?

Does the emf of the battery in (Fig. Below) affect the time1 o kkt qelu;o2;5n7kt needed for the LR circuit tn1 u2 te ol;ko7;5tkkqo 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 e,5w+ nf*zfca
(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 so6gw5xnlv:ux b :-prw1 bm)0xw urce emf affects the impedance of
(a) a pure resistance,
(b) a pure capacitance,
(c) a pure inductance,
(d) an LRC circuit near resonance (R small),
(e) an LRC circuit far from resonance (R small).

Describe how to make the impedance in an6lc l4ms,r hy2 LRC circuit a minimum.

  The magnetic flux through a coil of wji/4 ,,tdw iqizgo:u4ire containing two loops changes from -50Wb to +38 Wb in 0.42 s. What is the emf induced inoz,ui4,dtjwiq /:gi4 the coil?    V

  The rectangular loop shown in (Fig. Below) is pushed t6oh)u+pg c;5/ix dnr ec:6esinto the magnetic field which points inward.cu ch ;esdongir:t 66px/e)+5 In what direction is the induced current?  ----待选择----counterclockwiseclockwise 

  The north pole of the magnet in (Fig. Below) is being /c *b,on4pd yfinserted into the coil. In which *cd,4 f npoyb/direction is the induced current flowing through the resistor R?  ----待选择----from right to leftfrom left to right 

  A 9.6-cm-diameter circular loop of wir; qhdcwn :x:kej q27*ce is in a 1.10-T magnetic field. The loop is removed from the field i;:2:kqexq wn7 ch*d cjn 0.15 s. What is the average induced emf?    $ \times10^{-2 }\;V$

  A 12.0-cm-diameter loop of wire inh++ovp+)5e x d9opet s 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 emood9v 5 ph+tex++ pen)f in the loop?    $ \times10^{-2 }\;V$

  A 10.2-cm-diameter wire coil is initially oriented so that its/qh4nt)6jf3rp 9qz ae plane is perpendicular to a magnetic field of 0.63 T pointing up. During the couq4r tz/ nqfa69jh p)e3rse 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 in a 0.50-T magne5qc b7:d9qstzwg(u60l g: 3l qun0nqttic 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. B.z8) lux*nxrlf ey22 ielow) is slowly increased, what is the direction of the nx2i 28ul exf) lyzr.*current induced in the small circular loop inside the larger loop?  ----待选择----counterclockwiseclockwise 
(b) What would it be if the small loop were placed outside the larger one, to the left?  ----待选择----counterclockwiseclockwise 

  What is the direction of the induced current in the circular loop db1fm9du tk33bzz6/a)kv rk (d ue to the current shown in each part of (Fig. Belrak9tmkzdzb3fk)/b6u3(v1 d ow)?
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 the loop shown, in , x1olid,*l aqm tas8p9iqnf: f,67wjwhal,a1,f 6l a9moqpswf n ij,8ixd* qt7:t direction is the induced current in the loop?  ----待选择----counterclockwiseclockwise 

  The magnetic field perpendicular to a circular wire loop:a * uag2w+v rf97nbgp 12.0 cm in diameter is changed from +0.52T to -0.4f29 *p+agnwabv rug7:5 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 loncbz /xk,224w7 no 1i- fmlknufg and is pulled at a speed of 15.0cm/s If the magnetic field imkkflnu fx7,wi-z2c 14 b2 /ons 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,(+q ee.oym**eyc5qq0gqmy bo,.miv: +kt k v paper lies in a 0.75-T magnetic field pointing into the paper. If tqqyg 0. y(ykvo,,vmieq*. m:++e qb e tmc*5kohe 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 13h3vg7 sms.. qta26z 126jq drqzdgo*r.2 cm long and generates an emf of 120 mV while moving in a 0.90-t*q gzd6vgs7 .q6adohq r s32.mz21jrT 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 lk 2/ru0gji-hara )gbn7s(y.4:epc q of wire with dimensions shown in (Fig. Below) is situated inside a region of un4j ehnl/. riqb:gars-ag cp)0 2(7yukiform 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 cm. A 10-turn j1ml(ex:dl :vcoil is wound tightly around the center of the solenoid. If the current in the sl(jl:1x mdev:olenoid 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.y2o46 wcedyz *0,zgmi0 cm long, and has a resista24z0gioe yzcyw ,* 6mdnce 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 , yksx h;wt t6jxvpve2:o266rturns of circular copper wire 2.6 mm in diameter. A uniform magnetic field, perpendicular to the plane of the coil, chan,w66e2to r2t sxp;vj6y kvxh: ges 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 sing0,7o3td wehq8 cc4yrkdlw01 zle 13.2-cm-diameter circular loop of copper wire decreases uniformly from 0.750 T1d ,ylec7rh8c00dt4 zw wk qo3 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 outp gcjsnp oqfvoq u+/1ve u28*ayi* 4i((ut voltage of 24.0 V. The square armature consists of windigi 8 ae*n/q vop(2yio quv14 (fscju*+ngs 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 armature? $\approx$    loops(Round to the nearest integer)

  The generator of a car idling at 11ge2-l: -xa:ilf fts .v9s laug2ej2e,00 rpm produces 12.4 V. What will the ou tput be at a rotation speed of 2500 rpm, assuming nothi 9l--g atu.f, vje 2ga xfss2:ll2ee:ing else changes?    V

Show that the rms output (Sectur zrk 35i( h6;1dcllqion 18–7) of an ac generator is $V_\mathrm{rms}=NAB\omega/\sqrt{2}$, where $\omega=2\pi f.$

  A simple generator has a 3203g-/wtsc(on+9dds sj-loop square coil 21.0 cm on a side. How fast must it turn in a 0.650-T field to produce a 120-V peak o+/ d( wgc3tjssn9d o-sutput? $f$   rev/s

  A 450-loop circular armature c *kuuejljj31o.p (h2 toil with a diameter of 8.0 cm rotates at 120rev/s in a unifore*ou. j(pl1 jh tj2u3km 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. s7k*7sb/ke8mmcu0, ecl gl*k030 T. It has 1000 turns and produces ae0mc,/7 kc *8elb* m7slk guskn 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 resistance of nc uw, 9( w)6fkfq1iqz$3.25\Omega.$ If it draws 8.20 A when running at full speed and connected to a 120-V line, how large is the back emf?    V

  The back emf in a motor is 72 V when operating at 1800 rpm. What would be s)w*kwz2ly 11jf1op lthe back emf at 2500 rpm if the magnetpw)11 *llzyks 1jwof2 ic field is unchanged?    V

  The back emf in a motor is 95 V when the motor is operating at 1000 rpm. How (tv 3q:uyugr bbcin2 9u zi2.)would you change the motor’s magnetic field if you wanted to reduce the back emf to 65 V when the motor was running 2(bbuqi n:ri)c2 zgt3uv.9 uyat 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 caun,wma u 6/qo7yses it to run at half sm yaow uq,/n67peed?    A

  A transformer is designed to change 120 V into 10,000 V+t cn 25rkf(by, and there are 164 turns in the primary coil. How many turns are in the secondary coiytk+ b5cnr (f2l? $\frac{V_\mathrm{s}}{V_\mathrm{p}}$ $\approx$    turns

  

  A step-up transformer increases 25 V to 120 V. Wh1a1g 7am5w 5sj ppdtxj9p3; iuuf12oqat is the current in the secondary coil as compared to the primarygjm5p9t1uqpfi ;s o12jw7px5a1u d 3a coil?   

  Neon signs require 12 kV for their operation. To operate from a 240-V l)-( qjhzz-c6ky wk x2:hq;ufeine, what must be the ratiou) q (h- q xew6:k;zjcz2h-kfy of secondary to primary turns of the transformer? What would the voltage output be if the transformer were connected backward?
$\frac{N_\mathrm{s}}{N_\mathrm{p}}$ =   
$V_s$ =    V

  A model-train transf zwx3 2bj4yq)xormer plugs into 120-V ac and draws 0.35 A while supplying 7.5 A to the32qz)y4 wx jxb 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 o xg zma6:0i -n(;wm.dycixyh,f a 95-W transformer is 12 V, and the input current is 22 A.ziw6dyn,gxh xc-i m (; m.:ay0
(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/ph;ou-zf)+igz,q t d primary turns and 1340 secondary turns. The input voltage is 120 V and the output current is 15.0 A. What are th;) duoqt,zh/pz-+ fi ge 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 mavdsaios1. 3wo7/mj -m (j:(ewkej 7town 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 rj327joyv9o :xk wg )bi6e, pykf; /cga town over two $0.100-\Omega$ lines. Estimate how much power is saved if the voltage is stepped up from 120 V to 1200 V and then down again, rather than simply transmitting at 120 V. Assume the transformers are each 99% efficient.    kW

  If the current in a 180-mH coil changes steadily 5ozuwd/2nr0*nhvzp 8from 25.0 A to 10.0 A in 350 ms, what is the magnitude of the indud z2 wz*5hu/pr8nv on0ced emf?    V

  What is the inductance of a coil if the coil produces 6c) d8 di981yef;nr8qgdt aavan emf of 2.50 V when the currentny8 rad1a9) i; vtqf8c86dedg in it changes from -28.0mA to +31.0mA in 12.0 ms?    H

  What is the inductance L of0eh;i wpb :n5d a 0.60-m-long air-filled coil 2.9 cm in diameter containing wbh :e i0;5ndp10,000 loops?    H

  How many turns of wire would be required to make a ct 4v t s3:nni+ko+zm*130-mH inductance out of a 30.+mitnok4:+3 tzcv n s*0-cm-long air-filled coil with a diameter of 5.2 cm? L$\approx$    turns (Round to the nearest integer)

  An air-filled cylindrical inductor has 2800 turns, and it is +zdaue:j:be /nb)d+*hsj/q.foc; w a2.5 cm in diameter and 2 ds a/be + :+)z.newaj* bofq;/jcdhu:8.2 cm long.
(a) What is its inductance?    $ \times10^{-2 }\;H$
(b) How many turns would you need to generate the same inductance if the core were iron-filled instead? Assume the magnetic permeability of iron is about 1200 times that of free space.

  A coil has $2.25-\Omega$ resistance and 440-mH inductance. If the current is 3.00 A and is increasing at a rate of 3.50A/s what is the potential difference across the coil at this moment?    V

A long thin solenoid of length l and cross-sectional area A conp,hd62vj y ucwyy;p/:hklt izh4(k) 1tains $N_1$ 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 anott: m:r(znmz:jkd 6i6 iher tightly wound solenoid of twice the diameter. By what fart: k i::izdmj66mnz( ctor does the inductance change?   

  The magnetic field inside an air-filled solenoid 36 cm long ande h/2ywx2pno3h +jp q:3fwfa9 2.0 cm in diameter is 0.80 T. Approximate+p 9hp:2 af2qywj3fwxn h/oe3ly how much energy is stored in this field?    J

  At a given instant the current through an inductor is 50.j) porw9uxi :: gn)k 9oz6cma20 mA and is increasing at the rate of 115mA/s. What is the initial e9 :ji2c o)p:6o wx z9k)anurmgnergy stored in the inductor if the inductance is known to be 60.0 mH, and how long does it take for the energy to increase by a factor of 10 from the initial value?
U =    $ \times10^{-5}\;J$
$\Delta$t=    s

  Assuming the Earth’s magnwblqpw50ycl9 ad a4rk-,3qr9 etic 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 (Fig. Below) reach withie/af-y oq;9r+ eo.e/6s)cqau4fdu j s n
(a) 10%,    $\tau$
(b) 1.0%,    $\tau$
(c) 0.1% of its maximum value?    $\tau$

  Two tightly wound solenoids have the same length andolbksc8z o;yy +01 q0e circular cross-sectional area. But solenoid 1 uses wire that i0 o8+ s eb1zl;oykyqc0s 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 reactanc; opr*8qk .wdie 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-z08 y-ei5/ zzstu .oekq5qc)pmH inductor have a reactance of $660 \mathrm{k} \Omega ?$    Hz

  At what frequency will cncu +y-x1ou2a $2.40-\mu F$ capacitor have a reactance of $6.70 \mathrm{k} \Omega ?$    Hz

Plot a graph of the reactance of(uy0g q 5bqvc8 a $1.0-\mu F$ capacitor as a function of frequency from 10 to 1000 Hz.

Plot a graph of the reactance of r2w*l3l4i5o 0p p /o v(dmirwra 1.0-mH inductor as a function of frequency fr05ll rw4*3v di/wp m2r prioo(om 100 to 10,000 Hz.

  Calculate the reactanqtb,5gz3 vlvln 6 )j-lce of, and rms current in, a 160-mH radio coil connected to a 24-z6n5,lbvlg qj)v3 lt0-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 drawq:da f+ 4tjae,d agfms8 ef3uark6b6pq4c+1/ s 12.8 A. What is the coil’s induc tbdfa jmp+4qg afqrd/ue8eac,16 3fsa6k+:4tance? $X_L$ =    $ \times10^{-2 }\;H$

  (a) What is the reactance of a well-insutwee .su),m)d lated $0.030-\mu F$ 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 passi;ofk dtj7n c/4ng through the human body for 1.0 s could be lkondtjc;47f/ ethal. What must be the impedance of the body for this to occur?    $ \times10^{3 }\;\Omega$

  What is the resistance of a coil if its impedance i snkfc5i c49;ps $\mathrm{235~Ω}$ and its reactance is $\mathrm{135~Ω}$    $\Omega$

  What are the total impedance, phase angle, and rms current in an r64bz:m tat;p(hdjk1 .;ozhk LRC circuit connecrdm;h ot 1(;t.a:zkkbhpjz 64ted to 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 wi: c4gagq8/u: qi ef82ciqigp2th a 420-mH inductor is driven by an ac power supply. At i8 pqgqqccaie:8ug2/:2 i4gfwhat frequency is the impedance double that of the impedance at 60 Hz?    Hz

  (a) What is the rms currenm1 2;z ha.jiepdc:y6 bywz50pt in an RL circuit when a 60.0-Hz 120-V rms ac voltage is applied,hzzp d w6 1.ep2cm0jyb;ya5i: where $R=1.80\mathrm{~k}\Omega,$ and $L=350\mathrm{~mH}?$    $ \times10^{ -2}\;A$
(b) What is the phase angle between voltage and current?    $^{\circ}\,$
(c) What are the rms voltage readings across R and L?
$V_{rms \,R}$ $\approx$    V (Round to the nearest integer)
$V_{rms\,L}$ =    V

  (a) What is the rms current in an RC ciix f6/ in/x*o 9md* /yv-vxuntrcuit 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 connected to ix30eo 7m5hfbl0j s(ga $55.0-\mu H$ 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 ccl5u b0s.39 lbod8unance of 2800 pF when the radio is tuned to a st.b9nc3 usuo5dc ll0b 8ation 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 4cpim-i1 yj, jtsi(pi+m(gy2 4.8 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 cufte8ttdslu - h3y:,hfu/i (o+rrent loops in the plane of the page as shown in (Fig. Below). When switch S is thrown in the lel:ydu/s(f - ttif8t+ e3hou h,ft-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 ruvmrq ) 4:4na2okx 5sqesistance 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 12 b) 1f309p jze(vaq t-trnq:f jj*3ewmV. It contains a transformer that converts 120-V housj( ver0 jmtqztbq1 :3 f*e9)pawfj-3n ehold 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 genera48k xg ec3;v afk1ogi,ting plant located 118 km from a town that requires 50 MW of power at 12 kV. Two transmission lines from the pkeg1g vk 3co8ax;if4,lant 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% effici bzgt,iua9,b l5l:x5 sency are connected to 110-V ac. Tlbix ,:a usl5bt59 z,ghe 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 transmis9e6:uh r/ijp)zzr; sosion lines each have a $0.80-\Omega$ resistance and carry 740 A over 9.0 km. If the rms input voltage is 42 kV, calculate
(a) the voltage at the other end, $\approx$    kV
(b) the power input, $\approx$    $ \times10^{7 }\;W$
(c) power loss in the lines, $\approx$   $ \times10^{5 }\;$W
(d) the power output. $P_{out}$ $\approx$    $ \times10^{7 }\;W$

  Two resistanceless rails rest 32 cm apart o 0ce/0njf:mgjs kl ,z0n 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, 3 zehp1*wkd9v$R_L$ 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 resizh4vgn8v va(8 x )q9dbstance 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 sur,q/p6:l kd jzjx2x.rvges in current. In particular, after the power is turned on the current should ris jplx:xr,. djv qz26k/e no more than 7.5 mA in the first $120\mu s$ The device has resistance $\mathrm{150~Ω}$ and is designed to operate at 55 mA. How would you protect this device? L $\approx$    in series(retain two decimal places)

  A 25-turn 12.5-cm-diameter coil is placed between tx6: *bu wo h4spn90qsyhe pole pieces of an electromagnet. Whso9bp yxh6 sw*n0q u:4en 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 120 V? $|\varepsilon|$    T/s

  Calculate the peak output vox6g) ft p n6y,7xfw*valtage of a simple generator 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 ofpnxx66 vy*t) ag7wf, f 120rev/s. $\varepsilon_{peak}$ =    V

  Typical large values for e2n:6xr2slyc wmmh580y hn t0electric and magnetic fields attained in laboratories are08yxm cs2rw02 nhyenh:mlt56 about $1.0\times10^4\mathrm{~V/m}$ and 2.0 T.
(a) Determine the energy density for each field and compare.
$u_E$ $\approx$    $ \times10^{-4 }\;J/m^3$
$u_B$ $\approx$    $ \times10^{6 }\;J/m^3$
$\frac{u_B}{u_E}$ =   $ \times10^{9 }\;$
(b) What magnitude electric field would be needed to produce the same energy density as the 2.0-T magnetic field?    $ \times10^{8 }\;V/m$

  What is the inductance L of the primary of a tranj 1 -nvzp 1yjw6z,xiq6sformer whose input is 220 V at 60.0 Hz if the current drawn is 5.8 A? Assume no current in the i,1zv1nj6z wqj py-x6 secondary.    H

  A 130-mH coil whose resistance q 5bd9yb95 .sppmy 5c,dsz8hfis $\mathrm{18.5~Ω}$ 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 abii sg9w.u8wum dgd.r*m( 8n, 36-V battery. When connected to a 60-Hz 120-V (rms) source, thegw.,nid8w8rmb imsdu*u9 g(. 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 withksf- l0wgd t7m0mc 2;+.pm p /nhoss+x $2.0-\Omega$ 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 defc yxjd.rtd+o2jm 2m05ined as the ratio of the voltage across the capacitor (or inductor) to the voltage across the resistor, at resonance. The larger the Q 2. y520+mrjdjtd xomc 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$